vaheeD khoshnouD

linux, mikrotik, macosx

How to linux and Open Source

Written by vaheeD on January 9, 2013
5.00 avg. rating (96% score) - 2 votes

Copyright (C) 2004 (GNU Free Documentation License) 
Last Updated: May EDT 2012
Currently 117 tips.


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TIP 1:

     Is NTP Working?

     STEP 1 (Test the current server):

          Try issuing the following command:

          $ ntpq -pn

           remote refid st t when poll reach delay offset jitter
           =================================================== 16 u - 64 0 0.000 0.000 4000.00

          The above is an example of a problem.
          Compare it to a working configuration.

          $ ntpq -pn

           remote refid st t when poll reach delay offset jitter
           + 2 u 107 128 377 25.642 3.350 1.012
  10 l 40 64 377 0.000 0.000 0.008
           + 3 u 34 128 377 21.138 6.118 0.398
           * .USNO. 1 u 110 128 377 33.69 9.533 3.534

     STEP 2 (Configure the /etc/ntp.conf):

          $ cat /etc/ntp.conf

            # My simple client-only ntp configuration.
            # ping -a shows the IP address
            # which is used in the restrict below
            server # local clock
            fudge stratum 10
            driftfile /etc/ntp/drift
            restrict default ignore
            restrict mask
            authenticate no

     STEP 3 (Configure /etc/ntp/step-tickers):

          The values for server above are placed in the "/etc/ntp/step-tickers" file

          $ cat /etc/ntp/step-tickers


          The startup script /etc/rc.d/init.d/ntpd will grab the servers in this
          file and execute the ntpdate command as follows:

             /usr/sbin/ntpdate -s -b -p 8

          Why? Because if the time is off ntpd will not start. The command above set the
          clock. If System Time deviates from true time by more than 1000 seconds, then,
          the ntpd daemon  will enter panic mode and exit.

     STEP 4 (Restart the service and check):

          Issue the restart command

            /etc/init.d/ntpd restart

          check the values for "ntpq -pn",
          which should match step 1.

             ntpq -pn


          Time is always stored in the kernel as the number of seconds since
          midnight of the 1st of January 1970 UTC, regardless of whether the
          hardware clock is stored as UTC or not.  Conversions to local time
          are done at run-time. So, it's easy to get the time in different
          timezones for only the current session as follows:

              $ export TZ=EST
              $ date
              Mon Aug  2 10:34:04 EST 2004

              $ export TZ=NET
              $ date
              Mon Aug  2 15:34:18 NET 2004

          The following are possible values for TZ:

              Hours From Greenwich Mean Time (GMT) Value Description
              0 GMT Greenwich Mean Time
              +1 ECT European Central Time
              +2 EET European Eastern Time
              +2 ART
              +3 EAT Saudi Arabia
              +3.5 MET Iran
              +4 NET
              +5 PLT West Asia
              +5.5 IST India
              +6 BST Central Asia
              +7 VST Bangkok
              +8 CTT China
              +9 JST Japan
              +9.5 ACT Central Australia
              +10 AET Eastern Australia
              +11 SST Central Pacific
              +12 NST New Zealand
              -11 MIT Samoa
              -10 HST Hawaii
              -9 AST Alaska
              -8 PST Pacific Standard Time
              -7 PNT Arizona
              -7 MST Mountain Standard Time
              -6 CST Central Standard Time
              -5 EST Eastern Standard Time
              -5 IET Indiana East
              -4 PRT Atlantic Standard Time
              -3.5 CNT Newfoundland
              -3 AGT Eastern South America
              -3 BET Eastern South America
              -1 CAT Azores

              DST timezone

              0      BST for British Summer.
              +400   ADT for Atlantic Daylight.
              +500   EDT for Eastern Daylight.
              +600   CDT for Central Daylight.
              +700   MDT for Mountain Daylight.
              +800   PDT for Pacific Daylight.
              +900   YDT for Yukon Daylight.
              +1000  HDT for Hawaii Daylight.
              -100   MEST for Middle European Summer,
                         MESZ for Middle European Summer,
                         SST for Swedish Summer and FST for French Summer.
              -700   WADT for West Australian Daylight.
              -1000  EADT for Eastern Australian Daylight.
              -1200  NZDT for New Zealand Daylight.

     The following is an example of setting the TZ environment variable
     for the timezone, only when timezone changes go into effect.

               $ export TZ=EST+5EDT,M4.1.0/2,M10.5.0/2

     Take a look at the last line "M10.5.0/2". What does it mean? Here is the

        Mm.w.d This  specifies  day  d (0 <= d <= 6) of week w (1 <= w <= 5) of
              month m (1 <= m <= 12).  Week 1 is the first week in which day d
              occurs and week 5 is the last week in which day d occurs.  Day 0
              is a Sunday.

              The time fields specify when, in the local time  currently  in
              effect, the  change  to  the  other  time  occurs.   If omitted,
              the default is  02:00:00.

      So this is what it means. M10 stands for October, the 5 is the fifth week
      that includes a Sunday (note 0 in M10.5.0/2 is Sunday). To see that it is
      the fifth week see the calendar below. The time change occurs a 2am in
      the morning. (Special Note: In 2007, DST was extended. See TIP 230).

                         Su Mo Tu We Th Fr Sa
                                         1  2
                          3  4  5  6  7  8  9
                         10 11 12 13 14 15 16
                         17 18 19 20 21 22 23
                         24 25 26 27 28 29 30

       Prove it. Take the following program sunrise, which can calcuates sunrise
       and sunset for an latitude and longitude. This program can be downloaded
       from the following location:

       Below is a bash script that will run the program for the next 100 days.

          #  program: next100days  Mike Chirico
          #  download:
          #  This will calculate the sunrise and sunset for
          #  latitude     39.95  Note must convert to degrees
          #  longitude  75.15  Note must convert to degrees
          for (( i=0; i <= 100; i++))
            sunrise    `date -d "+$i day" "+%Y %m %d"` $lat $long

       Take a look at the following sample output.

           $ export TZ=EST+5EDT,M4.1.0/2,M10.5.0/2
           $ ./next100days

          Sunrise  08-24-2004  06:21:12   Sunset 08-24-2004  19:43:42
          Sunrise  08-25-2004  06:22:09   Sunset 08-25-2004  19:42:12
          Sunrise  08-26-2004  06:23:06   Sunset 08-26-2004  19:40:41
          Sunrise  08-27-2004  06:24:03   Sunset 08-27-2004  19:39:09
          Sunrise  08-28-2004  06:25:00   Sunset 08-28-2004  19:37:37
          Sunrise  08-29-2004  06:25:56   Sunset 08-29-2004  19:36:04
          Sunrise  08-30-2004  06:26:53   Sunset 08-30-2004  19:34:31
          Sunrise  08-31-2004  06:27:50   Sunset 08-31-2004  19:32:57
          Sunrise  09-01-2004  06:28:46   Sunset 09-01-2004  19:31:22
          Sunrise  09-02-2004  06:29:43   Sunset 09-02-2004  19:29:47
          ..[values omitted ]
          Sunrise  10-28-2004  07:25:31   Sunset 10-28-2004  18:02:34
          Sunrise  10-29-2004  07:26:38   Sunset 10-29-2004  18:01:19
          Sunrise  10-30-2004  07:27:46   Sunset 10-30-2004  18:00:06
          Sunrise  10-31-2004  06:28:53   Sunset 10-31-2004  16:58:54
          Sunrise  11-01-2004  06:30:01   Sunset 11-01-2004  16:57:44
          Sunrise  11-02-2004  06:31:10   Sunset 11-02-2004  16:56:35

       Compare 10-30-2004 with 10-31-2004. Sunrise is an hour earlier because
       daylight saving time has ended, just as predicted.

       There is an easier way to switch between timezones. Take a look at the
       directory zoneinfo as follows:

            $ ls /usr/share/zoneinfo

            Africa      Chile    Factory    Iceland      Mexico    posix       UCT
            America     CST6CDT  GB         Indian       Mideast   posixrules  Universal
            Antarctica  Cuba     GB-Eire    Iran         MST       PRC         US
            Arctic      EET      GMT  MST7MDT   PST8PDT     UTC
            Asia        Egypt    GMT0       Israel       Navajo    right       WET
            Atlantic    Eire     GMT-0      Jamaica      NZ        ROC         W-SU
            Australia   EST      GMT+0      Japan        NZ-CHAT   ROK
            Brazil      EST5EDT  Greenwich  Kwajalein    Pacific   Singapore   Zulu
            Canada      Etc      Hongkong   Libya        Poland    SystemV
            CET         Europe   HST        MET          Portugal  Turkey

       TZ can be set to any one of these files. Some of these are directories and contain
       subdirectories, such as ./posix/America. This way you don not have to enter the
       timezone, offset, and range for dst, since it has already been calculated.

           $ export TZ=:/usr/share/zoneinfo/posix/America/Aruba
           $ export TZ=:/usr/share/zoneinfo/Egypt


          Also see  (TIP 27).
          Also see  (TIP 103) using chrony which is very similiar to ntpd.
          Note time settings can usually be found in /etc/sysconfig/clock

TIP 2:

     cpio works like tar, only better.

     STEP 1 (Create two directories with data ../dir1 an ../dir2)

          mkdir -p ../dir1
          mkdir -p ../dir2
          cp /etc/*.conf ../dir1/.
          cp /etc/*.cnf ../dir2/.

          Which will backup all your cnf and conf files.

     STEP 2 (Piping the files to tar)

          cpio works like tar but can take input
          from the "find" command.

           $ find ../dir1/ | cpio -o --format=tar > test.tar
           $ find ../dir1/ | cpio -o -H tar > test2.tar

          Same command without the ">"

           $ find ../dir1/ | cpio -o --format=tar -F test.tar
           $ find ../dir1/ | cpio -o -H tar -F test2.tar

          Using append

           $ find ../dir1/ | cpio -o --format=tar -F test.tar
           $ find ../dir2/ | cpio -o --format=tar --append -F test.tar

     STEP 3 (List contents of the tar file)

          $ cpio -it < test.tar
          $ cpio -it -F test.tar

     STEP 4 (Extract the contents)

          $ cpio -i -F test.tar

TIP 3:

     Working with tar. The basics with encryption.

     STEP 1 (Using the tar command on the directory /stuff)

          Suppose you have a directory /stuff
          To tar everything in stuff to create a ".tar" file.

          $ tar -cvf stuff.tar stuff

          Which will create "stuff.tar".

     STEP 2 (Using the tar command to create a ".tar.gz" of /stuff)

          $ tar -czf stuff.tar.gz stuff

     STEP 3 (List the files in the archive)

          $ tar -tzf stuff.tar.gz
          $ tar -tf stuff.tar

     STEP 4 (A way to list specific files)

          Note, pipe the results to a file and edit

           $ tar -tzf stuff.tar.gz > mout

          Then, edit mout to only include the files you want

           $ tar -T mout -xzf stuff.tar.gz

          The above command will only get the files in mout.
          Of couse, if you want them all

           $ tar -xzf stuff.tar.gz


           $ tar -zcvf - stuff|openssl des3 -salt -k secretpassword | dd of=stuff.des3

          This will create stuff.des3...don't forget the password you
          put in place of  secretpassword. This can be done interactively as

            $ dd if=stuff.des3 |openssl des3 -d -k secretpassword|tar zxf -

     NOTE:  above there is a "-" at the end... this will
            extract everything.

TIP 4:

     Creating a Virtual File System and Mounting it with a Loopback Device.

     STEP 1 (Construct a 10MB file)

           $ dd if=/dev/zero of=/tmp/disk-image count=20480

          By default dd uses block of 512 so the size will be 20480*512

     STEP 2 (Make an ext2 or ext3 file system) -- ext2 shown here.

           $ mke2fs -q

          or if you want ext3

           $ mkfs -t ext3 -q /tmp/disk-image

          yes, you can even use reiser, but you'll need to create a bigger
          disk image. Something like "dd if=/dev/zero of=/tmp/disk-image count=50480".

           $ mkfs -t reiserfs -q /tmp/disk-image

          Hit yes for confirmation.  It only asks this because it's a file

     STEP 3 (Create a directory "virtual-fs" and mount. This has to be done as root)

           $ mkdir /virtual-fs
           $ mount -o loop=/dev/loop0 /tmp/disk-image /virtual-fs

         SPECIAL NOTE: if you mount a second device you will have to increase the
                       loop count: loop=/dev/loop1, loop=/dev/loop2, ... loop=/dev/loopn

          Now it operates just like a disk. This virtual filesystem can be mounted
          when the system boots by adding the following to the "/etc/fstab" file. Then,
          to mount, just type "mount /virtual-fs".

                 /tmp/disk-image /virtual-fs ext2               rw,loop=/dev/loop0 0 0

     STEP 4 (When done, umount it)

           $ umount /virtual-fs

     SPECIAL NOTE: If you are using Fedora core 2, in the /etc/fstab you can take
              advantage of acl properties for this mount. Note the acl next to the
              rw entry. This is shown here with ext3.

                 /tmp/disk-image     /virtual-fs ext3    rw,acl,loop=/dev/loop1 0 0

              Also, if you are using Fedora core 2 and above, you can mount the file
              on a cryptoloop.

                $ dd if=/dev/urandom of=disk-aes count=20480

                $ modprobe loop
                $ modprobe cryptoloop
                $ modprobe aes

                $ losetup -e aes /dev/loop0 disk-aes
                $ mkfs -t ext2 /dev/loop0
                $ mount -o loop,encryption=aes disk-aes <mount point>

              If you do not have Fedora core 2, then, you can build the kernel from source
              with some of the following options (not complete, yet)

                      Cryptographic API Support (CONFIG_CRYPTO)
                      generic loop cryptographic (CONFIG_CRYPTOLOOP)
                      Cryptographic ciphers (CONFIG_CIPHERS)
                      Enable one or more  ciphers  (CONFIG CIPHER .*) such as AES.

     HELPFUL INFORMATION: It is possible to bind mount partitions, or associate the
                     mounted partition to a directory name.

                  # mount --bind  /virtual-fs      /home/mchirico/vfs

             Also, if you want to see what filesystems are currently mounted, "cat" the
             file "/etc/mtab"

                  $ cat /etc/mtab

     Also see TIP 91.

TIP 5:

     Setting up 2 IP address on "One" NIC. This example is on ethernet.

     STEP 1 (The settings for the initial IP address)

           $ cat /etc/sysconfig/network-scripts/ifcfg-eth0


     STEP 2 (2nd IP address: )

           $ cat /etc/sysconfig/network-scripts/ifcfg-eth0:1


     SUMMARY  Note, in STEP 1 the filename is "ifcfg-eth0", whereas in
              STEP 2 it's "ifcfg-eth0:1" and also not the matching
              entries for "DEVICE=...".  Also, obviously, the
              "IPADDR" is different as well.

TIP 6:

     Sharing Directories Among Several Users.

     Several people are working on a project in "/home/share"
     and they need to create documents and programs so that
     others in the group can edit and execute these documents
     as needed. Also see (TIP 186) for adding existing users
     to groups.

       $  /usr/sbin/groupadd share
       $  chown -R root.share /home/share
       $  /usr/bin/gpasswd -a <username> share
       $  chmod 2775 /home/share

       $  ls -ld /home/share
             drwxrwsr-x    2 root     share        4096 Nov  8 16:19 /home/share
                   ^---------- Note the s bit, which was set with the chmod 2775

       $  cat /etc/group
          ...          ^------- users are added to this group.

     The user may need to login again to get access. Or, if the user is currently
     logged in, they can run the following command:

       $ su - <username>

     Note, the above step is recommended over  "newgrp - share" since currently
     newgrp in FC2,FC3, and FC4 gets access to the group but the umask is not
     correctly formed.

     As root you  can test their account.

       $ su - <username>   "You need to '-' to pickup thier environment  '$ su - chirico' "

     Note: SUID, SGID, Sticky bit. Only the left most octet is examined, and "chmod 755" is used
          as an example of the full command. But, anything else could be used as well. Normally
          you'd want executable permissions.

        Octal digit  Binary value      Meaning                           Example usage
            0           000       all cleared                             $ chmod 0755 or chmod 755
            1           001       sticky                                  $ chmod 1755
            2           010       setgid                                  $ chmod 2755
            3           011       setgid, sticky                          $ chmod 3755
            4           100       setuid                                  $ chmod 4755
            5           101       setuid, sticky                          $ chmod 5755
            6           110       setuid, setgid                          $ chmod 6755
            7           111       setuid, setgid, sticky                  $ chmod 7755

     A few examples applied to a directory below. In the first example all users in the group can
     add files to directory "dirA" and they can delete their own files. Users cannot delete other
     user's files.

        Sticky bit:
           $ chmod 1770  dirA

     Below files created within the directory have the group ID of the directory, rather than that
     of the default group setting for the user who created the file.

        Set group ID bit:
           $ chmod 2755  dirB

TIP 7:

     Getting Infomation on Commands

     The "info" is a great utility for getting information about the system.
     Here's a quick key on using "info" from the terminal prompt.

       'q' exits.
       'u' moves up to the table of contents of the current section.
       'n' moves to the next chapter.
       'p' moves to the previous chapter.
       'space' goes into the selected section.

      The following is a good starting point:

        $ info coreutils

      Need to find out what a certain program does?

        $ whatis  open
       open   (2)  - open and possibly create a file or device
       open   (3)  - perl pragma to set default PerlIO layers for input and output
       open   (3pm)  - perl pragma to set default PerlIO layers for input and output
       open   (n)  - Open a file-based or command pipeline channel

      To get specific information about the open commmand

        $ man 2 open

       also try 'keyword' search, which is the same as the apropos command.
       For example, to find all the man pages on selinux, type the following:

        $ man -k selinux

       or the man full word search. Same as whatis command.

        $ man -f <some string>

       This is a hint once you are inside man.

        space      moves forward one page
        b          moves backward
        y          scrolls up one line "yikes, I missed it!"
        g          goes to the beginning
        q          quits
        /<string>  search, repeat seach n
        m          mark, enter a letter like "a", then, ' to go back
        '          enter a letter that is marked.

       To get section numbers

        $ man 8 ping

       Note the numbers are used as follows
         (This is OpenBSD)

         1  General Commands
         2  System Calls and Error Numbers
         3  C Libraries
         3p perl
         4  Devices and device drivers
         5  File Formats and config files
         6  Game instructions
         7  Miscellaneous information
         8  System maintenance
         9  Kernel internals

       To find the man page directly, "ls" command:

         $ whereis -m ls
         ls: /usr/share/man/man1/ls.1.gz /usr/share/man/man1/ls.1 /usr/share/man/man1p/ls.1p

       To read this file directly, do the following:

         $ man /usr/share/man/man1/ls.1.gz

       If you want to know the manpath, execute manpath.

         $ manpath

TIP 8:

     How to Put a "Running Job" in the Background.

     You're running a job at the terminal prompt, and it's taking
     a very long time. You want to put the job in the backgroud.

       "CTL - z" Temporarily suspends the job
       $ jobs     This will list all the jobs
       $ bg %jobnumber (bg %1)  To run in the background
       $ fg %jobnumber          To bring back in the foreground

     Need to kill all jobs -- say you're using several suspended
     emacs sessions and you just want everything to exit.

       $ kill -9  `jobs -p`

     The "jobs -p" gives the process number of each job, and the
     kill -9 kills everything. Yes, sometimes "kill -9" is excessive
     and you should issue a "kill -15" that allows jobs to clean-up.
     However, for exacs session, I prefer "kill -9" and haven't had
     a problem.

     Sometimes you need to list the process id along with job
     information. For instance, here's process id with the listing.

       $ jobs -l

     Note you can also renice a job, or give it lower priority.

       $ nice -n +15 find . -ctime 2 -type f  -exec ls {} \; > last48hours
       $  bg

     So above that was a ctl-z to suppend. Then, bg to run it in
     the background. Now, if you want to change the priority lower
     you just renice it, once you know the process id.

       $ jobs -pl
   [1]+ 29388 Running                 nice -n +15 find . -ctime 2 -exec ls -l {} \; >mout &

       $ renice +30 -p 29388
        29388: old priority 15, new priority 19

      19 was the lowest priority for this job. You cannot increase
      the priority unless you are root.

TIP 9:

     Need to Delete a File for Good -- not even GOD can recover.

     You have a file "secret".  The following makes it so no one
     can read it.  If the file was 12 bytes, it's now 4096 after it
     has been over written 100 times.  There's no way to recover this.

       $ shred -n 100 -z secret

     Want to remove the file? Use the "u" option.

       $ shred -n 100 -z -u test2

     It can be applied to a device

       $ shred -n 100 -z -u /dev/fd0

       CAUTION: Note that shred relies on a very important assumption: that the file system  overwrites  data
       in  place.   This is the traditional way to do things, but many modern file system designs do not sat-
       isfy this assumption.  The following are examples of file systems on which shred is not effective,  or
       is not guaranteed to be effective in all file system modes:

       * log-structured or journaled file systems, such as those supplied with

              AIX and Solaris (and JFS, ReiserFS, XFS, Ext3, etc.)

     Also see (TIP 52).

TIP 10:

     Who and What is doing What on Your System - finding open sockets,
     files etc.

       $ lsof
          or as root
       $ watch lsof -i

     To list all open Internet files, use:

       $ lsof -i -U

     You can also get very specific about ports. Do this as root for low

       $ lsof -i TCP:3306

     Or, look at UDP ports as follows:

       $ lsof -i UDP:1812

       (See TIP 118)

     Also try fuser. Suppose you have a mounted file-system, and you need
     to umount it. To list the users on the file-system /work

       $ fuser -u /work

     To kill all processes accessing the file system /work  in  any way.

       $ fuser -km /work

     Or better yet, maybe you want to eject a cdrom on /mnt/cdrom

       $ fuser -km /mnt/cdrom

     If you need IO load information about your system, you can execute
     iostat. But note, the very first iostat gives a snapshot since
     the last boot. You typically want the following command, which gives
     you 3 outputs every 5 seconds.

       $ iostat -xtc 5 3
       Linux 2.6.12-1.1376_FC3smp (       10/05/2005

       Time: 07:05:04 PM
       avg-cpu:  %user   %nice %system %iowait   %idle
                  0.97    0.06    1.94    0.62   96.41

       Time: 07:05:09 PM
       avg-cpu:  %user   %nice %system %iowait   %idle
                  0.60    0.00    1.70    0.00   97.70

       Time: 07:05:14 PM
       avg-cpu:  %user   %nice %system %iowait   %idle
                  1.00    0.00    1.60    0.00   97.39

     vmstat reports memory statistics. See tip 241 for vmstat for
     I/O subsystem total statistics.

       $ vmstat
       $ ifconfig
       $ cat /proc/sys/vm/.. (entries under here)

      *NOTE: (TIP 77) shows sample usage of "ifconfig". Also
       (TIP 84) shows sample output of "$ cat /proc/cpuinfo". You can download iostat
       and other packages from (
       You also may want to look at iozone (TIP 178).


       $ cat /proc/meminfo
       $ cat /proc/stat

       $ cat /proc/uptime
       1078623.55 1048008.34       First number is the number of seconds since boot.
                                   The second number is the number of idle seconds.

       $ cat /proc/loadavg
       0.25 0.14 0.10 1/166 7778   This shows load at 1,5, and 15 minutes,
                                   a total of 1 current running process out
                                   from a total of 166. The 7778 is the last
                                   process id used.

     Or current process open file descriptors

        $ ls -l /proc/self/fd/0
            lrwx------    1 chirico  chirico        64 Jun 29 13:17 0 -> /dev/pts/51
            lrwx------    1 chirico  chirico        64 Jun 29 13:17 1 -> /dev/pts/51
            lrwx------    1 chirico  chirico        64 Jun 29 13:17 2 -> /dev/pts/51
            lr-x------    1 chirico  chirico        64 Jun 29 13:17 3 -> /proc/26667/fd

      So you could, $ echo "stuff" > /dev/pts/51, to get output. Note, tree is also
      helpful here:

         $ tree /proc/self

            |-- auxv
            |-- cmdline
            |-- cwd -> /work/souptonuts/documentation/theBook
            |-- environ
            |-- exe -> /usr/bin/tree
            |-- fd
            |   |-- 0 -> /dev/pts/51
            |   |-- 1 -> /dev/pts/51
            |   |-- 2 -> /dev/pts/51
            |   `-- 3 -> /proc/26668/fd
            |-- maps
            |-- mem
            |-- mounts
            |-- root -> /
            |-- stat
            |-- statm
            |-- status
            |-- task
            |   `-- 26668
            |       |-- auxv
            |       |-- cmdline
            |       |-- cwd -> /work/souptonuts/documentation/theBook
            |       |-- environ
            |       |-- exe -> /usr/bin/tree
            |       |-- fd
            |       |   |-- 0 -> /dev/pts/51
            |       |   |-- 1 -> /dev/pts/51
            |       |   |-- 2 -> /dev/pts/51
            |       |   `-- 3 -> /proc/26668/task/26668/fd
            |       |-- maps
            |       |-- mem
            |       |-- mounts
            |       |-- root -> /
            |       |-- stat
            |       |-- statm
            |       |-- status
            |       `-- wchan
            `-- wchan

            10 directories, 28 files

     Need a listing of the system settings?

       $ sysctl -a

     Need IPC (Shared Memory Segments, Semaphore Arrays, Message Queue) status

       $ ipcs
       $ ipcs -l  "This gives limits"

     Need to "watch" everything a user does?  The following watches donkey.

       $ watch lsof -u donkey

     Or, to see what in  going on in directory "/work/junk"

       $ watch lsof +D /work/junk

TIP 11:

     How to make a File "immutable" or "unalterable" -- it cannot be changed
     or deleted even by root. Note this works on (ext2/ext3) filesystems.
     And, yes, root can delete after it's changed back.

     As root:

       $ chattr +i filename

     And to change it back:

       $ chattr -i filename

     List attributes

       $ lsattr filename

TIP 12:

     SSH - How to Generate the Key Pair.

     On the local server

       $  ssh-keygen -t dsa -b 2048

     This will create the two files:

            .ssh/id_dsa (Private key)
            .ssh/  (Public key you can share)

     Next insert ".ssh/" on the remote server
     in the file  ".ssh/authorized_keys" and ".ssh/authorized_keys2"
     and change the  permission of each file to (chmod 600). Plus, make
     sure the directory ".ssh" exists on the remote computer with 700 rights.
     Ok, assuming is the remote server and "donkey" is the
     account on that remote server.

       $ ssh [email protected] "mkdir -p .ssh"
       $ ssh [email protected] "chmod 700 .ssh"
       $ scp ./.ssh/  [email protected]:.ssh/

     Now connect to that remote server "" and add .ssh/
     to both "authorized_keys" and "authorized_keys2".  When done, the permission
       (This is on the remote server)

        $chmod 600 .ssh/authorized_key*

     Next, go back to the local server and issue the following:

        $ ssh-agent $SHELL
        $ ssh-add

     The "ssh-add" will allow you to enter the passphrase and it will
     save it for the current login session.

     You don't have to enter a password when running "ssh-keygen" above. But,
     remember anyone with root access can "su - <username>" and then connect
     to your computers.  It's harder, however, not impossible, for root to do
     this if  you have a password.

     (Reference TIP 151)

     Below is a quick shell command to distribute ssh keys. I find
     this command to be very useful.

       $ cat ~/.ssh/|ssh remoteserver "cat - >> ~/.ssh/authorized_keys"

TIP 13:

     Securing the System: Don't allow root to login remotely.  Instead,
     the admin could login as another account, then, "su -".  However,
     root can still login "from the local terminal".

     In the "/etc/ssh/sshd_config" file change the following lines:

        Protocol 2
        PermitRootLogin no
        PermitEmptyPasswords no

     Then, restart ssh

        /etc/init.d/sshd restart

     Why would you want to do this?  It's not possible for anyone to guess
     or keep trying the root account.  This is especially good for computers
     on the Internet. So, even if the "root" passwords is known, they can't
     get access to the system remotely.  Only from the terminal, which is locked
     in your computer room. However, if anyone has a account on the server,
     then, they can login under their  account then "su -".

     Suppose you only want a limited number of users:  "mchirico" and "donkey".
     Add the following line to "/etc/ssh/sshd_config". Note, this allows access
     for chirico and donkey, but everyone else is denied.

         #  Once you add AllowUsers - everyone else is denied.
         AllowUsers mchirico donkey

TIP 14:

     Keep Logs Longer with Less Space.

     Normally logs rotate monthly, over writing all the old data.  Here's a
     sample "/etc/logrotate.conf" that will keep 12 months of backup
     compressing the logfiles

       $ cat /etc/logrotate.conf

             # see "man logrotate" for details
             # rotate log files weekly
             #chirico changes to monthly

             # keep 4 weeks worth of backlogs
             # keep 12 months of backup
             rotate 12

             # create new (empty) log files after rotating old ones

             # uncomment this if you want your log files compressed

             # RPM packages drop log rotation information into this directory
             include /etc/logrotate.d

             # no packages own wtmp -- we'll rotate them here
             /var/log/wtmp {
                 create 0664 root utmp
                 rotate 1

             # system-specific logs may be also be configured here.

       Note: see tip 1. The clock should always be correctly set.

TIP 15:

     What Network Services are Running?

          $ netstat -tanup

     or if you just want tcp services

          $ netstat -tanp


          $ netstat -ap|grep LISTEN|less

     This can be helpful to determine the services running.

     Need stats on dropped UDP packets?

          $ netstat -s -u

     or TCP

          $ netstat -s -t

     or summary of everything

          $ netstat -s

     or looking for error rates on the interface?

          $ netstat -i

     Listening interfaces?

          $ netstat -l

     (Tip above provided by Amos Shapira)

     Also see TIP 77.

TIP 16:

     Apache: Creating and Using an ".htaccess" File

     Below is a sample ".htaccess" file which goes in
     "/usr/local/apache/htdocs/chirico/alpha/.htaccess" for this

         AuthUserFile /usr/local/apache/htdocs/chirico/alpha/.htpasswd
         AuthGroupFile /dev/null
         AuthName "Your Name and regular password required"
         AuthType Basic

         <Limit GET POST>
         require valid-user

    In order for this to work /usr/local/apache/conf/httpd.conf must
    have the following line in it:

       <Directory /usr/local/apache/htdocs/chirico/alpha>
           AllowOverride FileInfo AuthConfig Limit
           Options MultiViews Indexes SymLinksIfOwnerMatch IncludesNoExec
               Order allow,deny
               Allow from all
           <LimitExcept GET POST OPTIONS PROPFIND>
               Order deny,allow
               Deny from all

    Also, a password file must be created

      $ /usr/local/apache/bin/htpasswd -c .htpasswd chirico

    And enter the user names and passwords.

    Next Reload Apache:

      $ /etc/init.d/httpd reload

    (Reference TIP 213 limit access to certain directories based on IP address).

TIP 17:

     Working with "mt" Commands: reading and writing to tape.

     The following assumes the tape device is "/dev/st0"

     STEP 1 ( rewind the tape)

          # mt -f /dev/nst0 rewind

     STEP 2 (check to see if you are at block 0)

          # mt -f /dev/nst0 tell
            At block 0.

     STEP 3 (Backup "tar compress"  directories "one"  and "two")

          # tar -czf /dev/nst0 one two

     STEP 4 (Check to see what block you are at)

           # mt -f /dev/nst0 tell

       You should get something like block 2 at this point.

     STEP 5 (Rewind the tape)

           # mt -f /dev/nst0 rewind

     STEP 6 (List the files)

           # tar -tzf /dev/nst0

     STEP 7 (Restore directory "one"  into directory "junk").  Note, you
          have to first rewind the tape, since the last operation moved
          ahead 2 blocks. Check this with "mt -f /dev/nst0".

           # cd junk
           # mt -f /dev/nst0 rewind
           # mt -f /dev/nst0 tell
              At block 0.
           # tar -xzf /dev/nst0 one

     STEP 8 (Next, take a look to see what block the tape is at)

           # mt -f /dev/nst0 tell
              At block 2.

     STEP 9 (Now backup directories three  and four)

           # tar -czf /dev/nst0 three four

       After backing up the files, the tape should be past block 2.
       Check this.

           # mt -f /dev/nst0 tell
             At block 4.

          Currently the following exist:

                At block 1:

                At block 2:

                At block 4:
                    (* This is empty *)

     A few notes. You can set the blocking factor and a label
     with tar. For example:

      $ tar --label="temp label" --create  --blocking-factor=128 --file=/dev/nst0 Notes

     But note if you try to read it with the default, incorrect blocking
     factor, then, you will get the following error:

        $ tar -t   --file=/dev/nst0
        tar: /dev/nst0: Cannot read: Cannot allocate memory
        tar: At beginning of tape, quitting now
        tar: Error is not recoverable: exiting now

     However this is easily fixed with the correct blocking factor

         $ mt -f /dev/nst0 rewind
         $ tar -t --blocking-factor=128 --file=/dev/nst0
         temp label

     Take advantage of the label command.

         $ MYCOMMENTS="Big_important_tape"
         $ tar --label="$(date +%F)"+"${MYCOMMENTS}"

     Writing to tape on a remote computer

         $ tar cvzf - ./tmp | ssh -l chirico '(mt -f /dev/nst0 rewind; dd of=/dev/st0 )'

     Restoring the contents from tape on a remote computer

         $ ssh -l chirico '(mt -f /dev/nst0 rewind; dd if=/dev/st0  )'|tar xzf -

     Getting data off of tape with dd command with odd blocking factor. Just set ibs very high

         $ mt -f /dev/nst0 rewind
         $ tar --label="Contenets of Notes" --create  --blocking-factor=128 --file=/dev/nst0 Notes
         $ mt -f /dev/nst0 rewind
         $ dd ibs=1048576 if=/dev/st0 of=notes.tar

     The above will probably work with ibs=64k as well

        (Also see TIP 136)

TIP 18:

     Encrypting Data to Tape using "tar" and "openssl".

     The following shows an example of writing the contents of "tapetest" to tape:

        $ tar zcvf - tapetest|openssl des3 -salt  -k secretpassword | dd of=/dev/st0

     Reading the data back:

        $ dd if=/dev/st0|openssl des3 -d -k secretpassword|tar xzf -

TIP 19:

     Mounting an ISO Image as a Filesystem -- this is great if you don't have the DVD
         hardware, but, need to get at the data.  The following show an example of
         mounting the Fedora core 2 as a file.

         $ mkdir /iso0
         $ mount -o loop -t iso9660 /FC2-i386-DVD.iso  /iso0

     Or to mount automatically at boot, add the following to "/etc/fstab"

         /FC2-i386-DVD.iso /iso0     iso9660 rw,loop  0 0


TIP 20:

     Getting Information about the Hard drive and list all PCI devices.

                $ hdparm /dev/hda

                   multcount    = 16 (on)
                   IO_support   =  0 (default 16-bit)
                   unmaskirq    =  0 (off)
                   using_dma    =  1 (on)
                   keepsettings =  0 (off)
                   readonly     =  0 (off)
                   readahead    = 256 (on)
                   geometry     = 16383/255/63, sectors = 234375000, start = 0

            or for SCSI

                $ hdparm /dev/sda

            Try it with the -i option for information

                $ hdparm -i /dev/hda


                Model=IC35L120AVV207-1, FwRev=V24OA66A, SerialNo=VNVD09G4CZ6E0T
                Config={ HardSect NotMFM HdSw>15uSec Fixed DTR>10Mbs }
                RawCHS=16383/16/63, TrkSize=0, SectSize=0, ECCbytes=52
                BuffType=DualPortCache, BuffSize=7965kB, MaxMultSect=16, MultSect=16
                CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=234375000
                IORDY=on/off, tPIO={min:240,w/IORDY:120}, tDMA={min:120,rec:120}
                PIO modes:  pio0 pio1 pio2 pio3 pio4
                DMA modes:  mdma0 mdma1 mdma2
                UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
                AdvancedPM=yes: disabled (255) WriteCache=enabled
                Drive conforms to: ATA/ATAPI-6 T13 1410D revision 3a:  2 3 4 5 6

            How fast is your drive?

                $ hdparm -tT /dev/hda

                Timing buffer-cache reads:   128 MB in  0.41 seconds =315.32 MB/sec
                Timing buffered disk reads:  64 MB in  1.19 seconds = 53.65 MB/sec

            Need to find your device?

                $ mount
                $ cat /proc/partitions
                $ dmesg | egrep '^(s|h)d'

                   which for my system lists:

                      hda: IC35L120AVV207-1, ATA DISK drive
                      hdc: Lite-On LTN486S 48x Max, ATAPI CD/DVD-ROM drive
                      hda: max request size: 1024KiB
                      hda: 234375000 sectors (120000 MB) w/7965KiB Cache, CHS=16383/255/63, UDMA(100)

             By the way, if you want to turn on dma

                 $ hdparm -d1 /dev/hda
                   setting using_dma to 1 (on)
                   using_dma    =  1 (on)

         (Also see TIP 122 )

     List all PCI devices

                $ lspci -v

          00:00.0 Host bridge: Intel Corp. 82845G/GL [Brookdale-G] Chipset Host Bridge (rev
                  Subsystem: Dell Computer Corporation: Unknown device 0160
                  Flags: bus master, fast devsel, latency 0
                  Memory at f0000000 (32-bit, prefetchable) [size=128M]
                  Capabilities: <available only to root>

              ... lots more ...

           Note, there is also lspci -vv for even more information.

          (Also see TIP 200)

TIP 21:

     Setting up "cron" Jobs.

     If you want to use the emacs editor for editing cron jobs, then,
     set the following in your "/home/user/.bash_profile"


     Then, to edit cron jobs

        $ crontab -e

     You may want to put in the following header

        #MINUTE(0-59) HOUR(0-23) DAYOFMONTH(1-31) MONTHOFYEAR(1-12) DAYOFWEEK(0-6) Note 0=Sun and 7=Sun
        #14,15 10 * * 0   /usr/bin/somecommmand  >/dev/null 2>&1

     The sample "commented out command" will run at 10:14 and 10:15 every Sunday.  There will
     be no "mail" sent to the user because of the ">/dev/null 2>&1" entry.

        $ crontab -l

     The above will list all cron jobs. Or if you're root

        $ crontab -l -u <username>
        $ crontab -e -u <username>

     Reference "man 5 crontab":

        The time and date fields are:

                     field          allowed values
                     -----          --------------
                     minute         0-59
                     hour           0-23
                     day of month   1-31
                     month          1-12 (or names, see below)
                     day of week    0-7 (0 or 7 is Sun, or use names)

              A field may be an asterisk (*), which always stands for ``first-last''.

              Ranges of numbers are allowed.  Ranges are two numbers separated with a
              hyphen.   The  specified  range is inclusive.  For example, 8-11 for an
              ``hours'' entry specifies execution at hours 8, 9, 10 and 11.

              Lists are allowed.  A list is a set of numbers (or ranges) separated by
              commas.  Examples: ``1,2,5,9'', ``0-4,8-12''.

              Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".

     Note, you can run just every 5 minutes as follows:

              */5 * * * * /etc/mrtg/domrtg  >/dev/null 2>&1

     To run jobs hourly,daily,weekly or monthly you can add shell scripts into the
     appropriate directory:


     Note that the above are pre-configured schedules set in "/etc/crontab", so
     if you want, you can change the schedule. Below is my /etc/crontab:

           $ cat /etc/crontab

           # run-parts
           01 * * * * root run-parts /etc/cron.hourly
           02 4 * * * root run-parts /etc/cron.daily
           22 4 * * 0 root run-parts /etc/cron.weekly
           42 4 1 * * root run-parts /etc/cron.monthly

TIP 22:

     Keeping Files in Sync Between Servers.

     The remote computer is "" and has the account "donkey".  You want
     to "keep in sync" the files under "/home/cu2000/Logs" on the remote computer
     with files on "/home/chirico/dev/MEDIA_Server" on the local computer.

       $ rsync  -Lae ssh  [email protected]:/home/cu2000/Logs /home/chirico/dev/MEDIA_Server

     "rsync" is a convient command for keeping files in sync, and as shown here will work
     through ssh.  The -L option tells rsync to treat symbolic links like ordinary files.

        Also see []

TIP 23:

     Looking up the Spelling of a Word.

        $ look <partial spelling>

     so the following will list all words that
     start with stuff

        $ look stuff

     It helps to have a large "linuxwords" dictionary.  You can download
     a much bigger dictionary from the following:


     Note: vim users can setup the .vimrc file with the following. Now when you type 
       CTL-X CTL-T in insert mode, you'll get a thesaurus lookup.

           set dictionary+=/usr/share/dict/words
           set thesaurus+=/usr/share/dict/words

     Or, you can call aspell with the F6 command after putting the folling entry in your
     .vimrc file

           :nmap <F6> :w<CR>:!aspell -e -c %<CR>:e<CR>

     Now, hit F6 when you're in vim, and you'll get a spell checker.

     There is also an X Windows dictionary that runs with the following command.

           $ gnome-dictionary

TIP 24:

     Find out if a Command is Aliased.

         $ type -all <command>


         $ type -all ls
            ls is aliased to `ls --color=tty'
            ls is /bin/ls

TIP 25:

     Create a Terminal Calculator

      Put the following in your .bashrc file

            function calc
             echo "${1}"|bc -l;

      Or, run it at the shell prompt. Now
      "calc" from the shell will work as follows:

            $ calc 3+45

      All functions  with a "(" or ")" must be enclosed
      in quotes.  For instance, to get the sin of .4

            $ calc "s(.4)"

          (See TIP 115 using the expr command)

TIP 26:

     Kill a User and All Their Current Processes.

        #  This program will kill all processes from a
        #  user.  The user name is read from the command line.
        #  This program also demonstrates reading a bash variable
        #  into an awk script.
        #  Usage: kill9user <user>
        kill -9 `ps aux|awk -v var=$1 '$1==var { print $2 }'`

    or if you want want to create the above script the command
    below will kill the user "donkey" and all of his processes.

        $ kill -9 `ps aux|awk -v var="donkey" '$1==var { print $2 }'`

    Check their cron jobs and "at" jobs, if you have a security issue.

          $ crontab -u <user> -e

    Lock the account:

          $ passwd -l <user>

    Remove all authorized_keys

          $ rm /home/user/.shosts
          $ rm /home/user/.rhosts
          $ rm -rf /home/user/.ssh
          $ rm /home/user/.forward

      or consider

          $ mv /home/user  /home/safeuser

    Change the shell

          $ chsh -s /bin/true <user>

    Do an inventory

          $ find / -user <user>  > list_of_user_files

    NOTE: Also see (TIP 10).

    To see all users, except the current user. Do not use the
    dash "ps -aux" is wrong but the following is correct:

          $ ps aux| awk '!/'${USER}'/{printf("%s \n",$0)}'

     or (ww = wide, wide output)

          $ ps auwwx| awk '!/'${USER}'/{printf("%s \n",$0)}'

    The following codes may be useful:

       D    Uninterruptible sleep (usually IO)
       R    Running or runnable (on run queue)
       S    Interruptible sleep (waiting for an event to complete)
       T    Stopped, either by a job control signal or because it is being traced.
       W    paging (not valid since the 2.6.xx kernel)
       X    dead (should never be seen)
       Z    Defunct ("zombie") process, terminated but not reaped by its parent.

    For BSD formats and when the stat keyword is used, additional
       characters may be displayed:

       <    high-priority (not nice to other users)
       N    low-priority (nice to other users)
       L    has pages locked into memory (for real-time and custom IO)
       s    is a session leader
       l    is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
       +    is in the foreground process group

    Also see TIP 28. and TIP 89.

TIP 27:

     Format Dates for Logs and Files

         $ date "+%m%d%y %A,%B %d %Y %X"
             061704 Thursday,June 17 2004 07:13:40 PM

         $ date "+%m%d%Y"

         $ date -d '1 day ago' "+%m%d%Y"

         $ date -d '3 months 1 day  2 hour  15 minutes 2 seconds ago'

      or to go into the future remove the "ago"

         $ date -d '3 months 1 day  2 hour  15 minutes 2 seconds '

            Also the following works:

                $ date -d '+2 year +1 month -1 week  +3 day -8 hour +2 min -5 seconds'

      Quick question: If there are 100,000,000 stars in the visible sky, and you can
      count them, round the clock, at a rate of a star per second starting now, when
      would you finish counting?  Would you still be alive?

                $ date -d '+100000000 seconds'

      Sooner than you think!

      This can be assigned to variables

         $ mdate=`date -d '3 months 1 day  2 hour  15 minutes 2 seconds ' "+%m%d%Y_%A_%B_%D_%Y_%X"  `
         $ echo $mdate
             09182004_Saturday_September_09/18/04_2004_09:40:41 PM
             ^---- Easy to sort   ^-------^----- Easy to read

      See TIP 28 below.

      See TIP 87 when working with large delta time changes -40 years, or -200 years ago, or even
      1,000,000 days into the future.

      Also see (TIP 1) for working with time zones.

      See TIP 240 for converting epoch seconds to local time.

TIP 28:

     Need Ascii Codes? For instance, for printing quotes:

                         awk 'BEGIN { msg = "Don\047t Panic!"; printf "%s \n",msg }'
                         awk 'BEGIN { msg = "Don\x027t Panic!"; printf "%s \n",msg }'

     It's better to use \047, because certain characters that follow \x027 may cause problems.

     For example, take a look at the following two lines. The first line prints a "}" caused
     by the extra D in \x027D. The the line immediately below does not work as expected.

                      awk 'BEGIN {printf("The D causes problems \x027D\n")}'

            However, the line below works fine:

                      awk 'BEGIN {printf("The D does not cause problems \047D\n")}'

     Or if you wanted to use the date command in "awk" to print date.time.nanosecond.timezone for
     each line of a file "test".

     The following date can be used in awk because the single quotes are enclosed within the
     double quotes.

             date '+%m%d%Y.%H%M%S.%N%z'

       $ awk 'BEGIN { "date '+%m%d%Y.%H%M%S.%N%z'" | getline MyDate  } { print MyDate,$0 }' < data

     But it's also possible to replace  "+"  with  \x2B,  "%" with \x25, and "d" with \x64 as follows:

       $ awk 'BEGIN { "date \x27\x2B\x25m\x25\x64\x25Y.\x25H\x25M\x25S.\x25N\x25z\x27" | getline MyDate  } { print MyDate,$0 }' < test

             07062004.113820.346033000-0400 bob 71
             07062004.113820.346033000-0400 tom 43
             07062004.113820.346033000-0400 sal 34
             07062004.113820.346033000-0400 bob 89
             07062004.113820.346033000-0400 tom 66
             07062004.113820.346033000-0400 sal 99

     For this example it's not needed because single quotes are used inside of double quotes; however, there may be times when
     hex replacement is easier.

       $ man ascii

        Oct   Dec   Hex   Char           Oct   Dec   Hex   Char
            000   0     00    NUL '\0'       100   64    40    @
            001   1     01    SOH            101   65    41    A
            002   2     02    STX            102   66    42    B
            003   3     03    ETX            103   67    43    C
            004   4     04    EOT            104   68    44    D
            005   5     05    ENQ            105   69    45    E
            006   6     06    ACK            106   70    46    F
            007   7     07    BEL '\a'       107   71    47    G
            010   8     08    BS  '\b'       110   72    48    H
            011   9     09    HT  '\t'       111   73    49    I
            012   10    0A    LF  '\n'       112   74    4A    J
            013   11    0B    VT  '\v'       113   75    4B    K
            014   12    0C    FF  '\f'       114   76    4C    L
            015   13    0D    CR  '\r'       115   77    4D    M
            016   14    0E    SO             116   78    4E    N
            017   15    0F    SI             117   79    4F    O
            020   16    10    DLE            120   80    50    P
            021   17    11    DC1            121   81    51    Q
            022   18    12    DC2            122   82    52    R
            023   19    13    DC3            123   83    53    S
            024   20    14    DC4            124   84    54    T
            025   21    15    NAK            125   85    55    U
            026   22    16    SYN            126   86    56    V
            027   23    17    ETB            127   87    57    W
            030   24    18    CAN            130   88    58    X
            031   25    19    EM             131   89    59    Y
            032   26    1A    SUB            132   90    5A    Z
            033   27    1B    ESC            133   91    5B    [
            034   28    1C    FS             134   92    5C    \   '\\'
            035   29    1D    GS             135   93    5D    ]
            036   30    1E    RS             136   94    5E    ^
            037   31    1F    US             137   95    5F    _
            040   32    20    SPACE          140   96    60    `
            041   33    21    !              141   97    61    a
            042   34    22    "              142   98    62    b
            043   35    23    #              143   99    63    c
            044   36    24    $              144   100   64    d
            045   37    25    %              145   101   65    e
            046   38    26    &              146   102   66    f
            047   39    27    '              147   103   67    g
            050   40    28    (              150   104   68    h
            051   41    29    )              151   105   69    i
            052   42    2A    *              152   106   6A    j
            053   43    2B    +              153   107   6B    k
            054   44    2C    ,              154   108   6C    l
            055   45    2D    -              155   109   6D    m
            056   46    2E    .              156   110   6E    n
            057   47    2F    /              157   111   6F    o
            060   48    30    0              160   112   70    p
            061   49    31    1              161   113   71    q
            062   50    32    2              162   114   72    r
            063   51    33    3              163   115   73    s
            064   52    34    4              164   116   74    t
            065   53    35    5              165   117   75    u
            066   54    36    6              166   118   76    v
            067   55    37    7              167   119   77    w
            070   56    38    8              170   120   78    x
            071   57    39    9              171   121   79    y
            072   58    3A    :              172   122   7A    z
            073   59    3B    ;              173   123   7B    {
            074   60    3C    <              174   124   7C    |
            075   61    3D    =              175   125   7D    }
            076   62    3E    >              176   126   7E    ~
            077   63    3F    ?              177   127   7F    DEL

TIP 29:

     Need a WWW Browser for the Terminal Session? Try lynx or elinks.

         $ lynx

     Or to read all these tips, with the latest updates

      $ lynx

     Or, better yet elinks.

         $ elinks http://somepage.

     You can get elinks at the following site:


TIP 30:

    screen - screen manager with VT100/ANSI terminal emulation

         This is an excellent utility. But if you work a lot in Emacs,
         then, you should place the following in your ~/.bashrc

             alias s='screen -e^Pa -D -R'

         After loging in again (or source .bashrc) ,
         type the following to load "screen":

             $ s

         If you're using the not using the alias command above, substitute
         CTL-a for CTL-p below. :

             CTL-p CTL-C       To get a new session
             CTL-p  "           To list sessions, and arrow keys to move
             CTL-p SHFT-A      To name sessions
             CTL-p S            To split screens
             CLT-p Q            To unsplit screens
             CLT-p TAB          To switch between screens
             CLT-p :resize n    To resize screen to n rows, on split screen

         Screen is very powerful.  Should you become disconneced, you can
         still resume work after loggin in.

             $ man screen

         The above command will give you more information.

TIP 31:

     Need to Find the Factors of a Number?

           $ factor 2345678992
                2345678992: 2 2 2 2 6581 22277

     It's a quick way to find out if a number is prime

           $ factor 7867
                7867: 7867

TIP 32:

     Less is More -- piping to less to scroll backword and forward

      For large "ls" listings try the followin, then, use the arrow key
      to move up and down the list.

           $ ls /some_large_dir/ | less


           $ cat some_large_file | less


           $ less some_large_file

TIP 33:

     C "indent" Settings for Kernel Development

           $ indent -kr -i8  program.c

TIP 34:

     FTP auto-login.  "ftp" to a site and have the password stored.

     For instance, here's a sample ".net" file in a user's home
     directory for uploading to sourceforge. Note, sourceforge will
     take any password, so [email protected] is used here for login "anonymous".

           $ cat ~/.netrc
               machine login anonymous password [email protected]
               default login anonymous password [email protected]

     It might be a good idea to change the rights on this file

           $ chmod 0400 ~/.netrc

         #  Sample ftp automated script to download
         #  file to ${dwnld}
         cd ${dwnld}
         ftp << FTPSTRING
         prompt off
         cd /pub/usenet-by-group/news.answers/unix-faq/faq
         mget contents
         mget diff
         mget part*

     Sourceforge uses an anonymous login with an email address as
     a password. Below is the automated script I use for uploading 
     binary files.

        # ftp sourceforge auto upload
        #   Usage: ./ <filename>
        # machine user anonymous [email protected]
        ftp -n -u <<  FTPSTRING
        user anonymous [email protected]
        cd incoming
        put ${1}

      (Also see TIP 114 for ncftpget, which is a very powerful restarting
                            ftp program)

TIP 35:

     Bash Brace Expansion

           $ echo f{ee,ie,oe,um}
                fee fie foe fum

     This works with almost any command

           $ mkdir -p /work/junk/{one,two,three,four}

TIP 36:

     Getting a List of User Accounts on the System

           $ cut -d: -f1 /etc/passwd | sort

     Note (Thanks to Philip Vanmontfort) you can also do the following:

           $ getent passwd|cut -d: -f1|sort

TIP 37:

     Editing a Bash Command

      Try typing a long command say, then, type "fc" for an easy way
      to edit the command.

           $ find /etc -iname '*.cnf' -exec grep -H 'log' {} \;
           $ fc

      "fc" will bring the last command typed into an editor, "emacs" if
      that's the default editor. Type "fc -l" to list last few commands.

      To seach for a command, try typing "CTL-r" at the shell prompt for
      searching. "CTL-t" to transpose, say "sl" was typed by you want "ls".

      Hints when using "fc: in emacs:

           ESC-b     move one word backward
           ESC-f     move one word forward
           ESC-DEL   kill one word backward
           CTL-k     kill point to end
           CTL-y     un-yank killed region at point

TIP 38:

     Moving around Directories.

     Change to the home directory:
          $ cd ~
          $ cd

     To go back to the last directory
          $ cd -

     Instead of "cd" to a directory try "pushd" and look
     at the can see a list of directories.

          $ pushd /etc
          $ pushd /usr/local

      Then, to get back "popd" or "popd 1"

      To list all the directories pushed on the stack
      use the "dirs -v" command.

          $ dirs -v
           0  /usr/local
           1  /etc
           2  /work/souptonuts/documentation/theBook

      Now, if you "pushd +1" you will be moved to "/etc", since
      is number "1" on the stack, and this directory will become

          $ pwd
          $ pushd +1
          $ pwd

          $ dirs -v
           0  /etc
           1  /work/souptonuts/documentation/theBook
           2  /usr/local

TIP 39:

     Need an Underscore after a Variable?

       Enclose the variable in "{}".

          $echo ${UID}_

       Compare to

          $echo $UID_

       Also try the following:

                $ m="my stuff here"
                $ echo -e ${m// /'\n'}

TIP 40:

     Bash Variable Offset and String Operators

        $ r="this is stuff"
        $ echo ${r:3}
        $ echo ${r:5:2}

      Note, ${varname:offset:length}

         ${varname:?message}  If varname exist and isn't null return value, else,
                              print var and message.

           $ r="new stuff"
           $ echo ${r:? "that's r for you"}
               new stuff
           $ unset r
           $ echo ${r:? "that's r for you"}
               bash: r:  that's r for you

         ${varname:+word}    If varname exist and not null return word. Else, return null.

         ${varname:-word}    If varname exist and not null return value. Else, return word.

      Working with arrays in bash - bash arrays.

           $ unset p
           $ p=(one two three)

           $ echo -e "${p[@]}"
           one two three


           $ echo -e "${p[*]}"
           one two three

           $ echo -e "${#p[@]}"

           $ echo -e "${p[0]}"

           $ echo -e "${p[1]}"

            Also see (TIP 95)

TIP 41:

     Loops in Bash

      The command below loops through directories listed in $PATH.

          $ path=$PATH:
          $ while [ $path ]; do echo " ${path%%:*} "; path=${path#*:}; done

       The command below will also loop through directories in your path.

          $ for dir in $PATH
          > do
          > ls -ld $dir
          > done
              drwxr-xr-x    2 root     root         4096 Jun 10 20:16 /usr/local/bin
              drwxr-xr-x    2 root     root         4096 Jun 13 23:12 /bin
              drwxr-xr-x    3 root     root        40960 Jun 12 08:00 /usr/bin
              drwxr-xr-x    2 root     root         4096 Feb 14 03:12 /usr/X11R6/bin
              drwxrwxr-x    2 chirico  chirico      4096 Jun  6 13:06 /home/chirico/bin

     Other ways of doing loops:

        for (( i=1; i <= 20; i++))
                        echo -n "$i "

     Note, to do it all on one line, do the following:

        $ for (( i=1; i <= 20; i++)); do echo -n "$i"; done

     Below, is an example of declaring i an integer so that you do not
     have to preface with let.

          $ declare -i i
          $ i=5;
          $ while (( $i > 1 )); do
          > i=i-1
          > echo $i
          > done

     You can also use "while [ $i -gt 1 ]; do"  in place of "while (( $i > 1 )); do"

     To get a listing of all declared values

          $ declare -i

     Try putting a few words in the file "test"

         $ while read filename; do echo  "- $filename "; done < test |nl -w1

     Or, using an array

                declare -a Array
                for i in `seq ${#Array[@]}`
                  echo $Array[$i-1]

         Also see (TIP 95 and TIP 133).

TIP 42:

     "diff" and "patch".

        You have created a program "prog.c", saved as this name and also copied
        to  "prog.c.old". You post "prog.c" to users.  Next, you make changes
        to prog.c

          $ diff -c prog.c.old prog.c > prog.patch

        Now, users can get the latest updates by running.

          $ patch < prog.patch

        By the way, you can make backups of your data easily.

          $ cp /etc/fstab{,.bak}

        Now, you do your edits to "/etc/fstab" and if you need
        to go back to the original, you can find it at

        Also consider sdiff with the -s option, to ignore spaces to
        compare differences side-by-side between two files. An example
        is listed below.

          $ sdiff -s file1 file2

TIP 43:

     "cat" the Contents of Files Listed in a File, in That Order.

       SETUP (Assume you have the following)

              $ cat file_of_files

              $ cat file1
                  This is the data in file1

              $ cat file 2
                  This is the data in file2

       So there are 3 files here "file_of_files" which contains the name of
       other files.  In this case "file1" and "file2". And the contents of
       "file1" and "file2" is shown above.

               $ cat file_of_files|xargs cat
                    This is the data in  file1
                    This is the data in  file2

     Also see (TIP 44, TIP 62 and TIP 235).

TIP 44:

     Columns and Rows -- getting anything you want.

     Assume you have the following file.

        $ cat data
           1 2 3
           4 5
           6 7 8 9 10
           11 12
           13 14

     How to you get everything in  2 columns?

        $ cat data|tr ' ' '\n'|xargs -l2
           1 2
           3 4
           5 6
           7 8
           9 10
           11 12
           13 14

    Three columns?

        $ cat data|tr ' ' '\n'|xargs -l3
           1 2 3
           4 5 6
           7 8 9
           10 11 12
           13 14

    What's the row sum of the "three columns?"

        $ cat data|tr ' ' '\n'|xargs -l3|tr ' ' '+'|bc


        $ tr ' ' '\n' < data |xargs -l3|tr ' ' '+'|bc

    NOTE "Steven Heiner's rule":

             cat one_file | program

           can always be rewritten as

             program < one_file

   Note: thanks to Steven Heiner ( the above can be
       shortened as follows:

               $ tr ' ' '\n' < data|xargs -l3|tr ' ' '+'|bc

          Need to "tr" from the stdin?

               $ tr "xy" "yx"| ... | ...

       But there is a the "Stephane CHAZELAS" condition here

         "Note that tr, sed, and awk mail fail on files containing '\0'
          sed and awk have unspecified behaviors if the input
          doesn't end in a '\n' (or to sum up, cat works for
          binary and text files, text utilities such as sed or awk
          work only for text files).

TIP 45:

     Auto Directory Spelling Corrections.

      To turn this on:

           $ shopt -s cdspell

      Now mispell a directory in the cd command.

           $ cd /usk/local
                   ^-------- still gets you to --

      What other options can you set? The following will list
      all the options:

           $ shopt -p

TIP 46:

     Record Eveything Printed on Your Terminal Screen.

            $ script -a <filename>

     Now start doing stuff and "everything" is appended to <filename>.
     For example

            $ script installation

            $ (command)

            $ (result)

            $ ...

            $ ...

            $ (command)

            $ (result)

            $ exit

     The whole session log is in the installation file that you can later
     read and/or cleanup and add to a documentation.

     This command can also be used to redirect the contents to another user,
     but you must be root to do this.

     Step 1 - find out what pts they are using.

            $ w

     Step 2 - Run script on that pts. After running this command below
              everything you type will appear on their screen.

            $ script /dev/pts/4

     Thanks to [email protected] for his contribution
     to this tip.

     Also reference TIP 208.

TIP 47:

     Monitor all Network Traffic Except Your Current ssh Connection.

           $ tcpdump -i eth0 -nN -vvv -xX -s 1500 port not 22

       Or to filter out port 123 as well getting the full length of the packet
       (-s 0), use the following:

           $ tcpdump -i eth0 -nN -vvv -xX -s 0 port not 22  and port not 123

       Or to filter only a certain host say

           $ tcpdump -i eth0 -nN -vvv -xX  port not 22 and host

     Just want ip addresses and a little bit of data, then,
     use this. The "-c 20" is to stop after 20 packets.

           $ tcpdump -i eth0 -nN  -s 1500 port not 22 -c 20

     If you're looking for sign of DOS attacks, the following show just the SYN
     packets on all interfaces:

           $ tcpdump 'tcp[13] & 2 == 2'

TIP 48:

     Where are the GNU Reference Manuals?


     Also worth a look the "Linux Documentation Project"


     and Red Hat manuals


TIP 49:

     Setting or Changing the Library Path.

     The following contains the settings to be added or deleted


     After this file is edited, you must run the following:

           $ ldconfig

     See "man ldconfig" for more information.

TIP 50:

     Working with Libraries in C

     Assume the following 3 programs:

      $ cat ./src/test.c

         int test(int t)
           return t;

      $ cat ./src/prog1.c

          program: prog1.c
          dependences: test.c

          compiling this program:
          gcc -o prog test.c prog1.c

          Note the libpersonal include
          should be remove if NOT using the

         #include <libpersonal.h>
         #include <stdio.h>
         main(int argc, char **argv)

      $ cat ./include/libpersonal.h

         extern int test(int);

     Prog1.c needs the test function in  test.c
     To compile, so that both programs work together, do the following:

          $ cd src
          $ gcc -o prog test.c prog1.c -I../include

     However, if you want to create your own static library, then, run the following:

          $ mkdir -p ../lib
          $ gcc -c test.c  -o ../lib/test.o
          $ cd ../lib
          $ ar r libpersonal.a test.o
          $ ranlib libpersonal.a

     or, the ar and ranlib command can be combined as follows:

          $ ar rs libpersonal.a test.o

     To compile the program with the static library:

          $ cd ../src
          $ gcc -I../include -L../lib -o prog1 prog1.c -lpersonal

     The -I../include  tells  gcc to look in the ../include directory for
     libpersonal.h. and -L../lib, tells gcc to look for the
     "libpersonal.a" library.

           $ cd ..
           $ tree src lib include
           |-- prog
           |-- prog1
           |-- prog1.c
           `-- test.c
           |-- libpersonal.a
           `-- test.o
           `-- libpersonal.h

     This was a STATIC library. Often times you will want to use a SHARED
     or dynamic library.


     You must recompile test.c with -fpic option.

          $ cd ../lib
          $ gcc -c -fpic ../src/test.c -o test.o

     Next create the file.

          $ gcc -shared -o test.o

     Now, compile the source prog1.c as follows:

          $ cd ../src
          $ gcc -Wl,-R../lib -L../lib -I../include -o prog2 prog1.c -lpersonal

     This should work fine. But, take a look at prog2 using the ldd command.

          $ ldd prog2 => ../lib/ (0x40017000) => /lib/tls/ (0x42000000)
        /lib/ => /lib/ (0x40000000)

     If you move the program prog2 to a different location, it will not run.
     Instead you will get the following error:

           prog2: error while loading shared libraries:
                     cannot open shared object file: No such file or directory

     To fix this, you should specify the direct path to the library. And in my
     case it is rather long

      $  gcc -Wl,-R/work/souptonuts/documentation/theBook/lib -L../lib -I../include -o prog2 prog1.c -lpersonal

     SPECIAL NOTE: The -R must always follow the -Wl.  (-Wl,-R<directory>) They always go together

TIP 51:

     Actively Monitor a File and Send Email when Expression Occurs.

     This is a way to monitor "/var/log/messages" or any file for certain changes.
     The example below actively monitors "stuff" for the work "now" and as soon as
     "now" is added to the file, the contents of msg are sent to the user
     [email protected]

          $ tail -f stuff | \
              awk ' /now/ { system("mail -s \"This is working\"  [email protected] < msg") }'

     Or, you can run a program, say get headings on slashdot from the program "getslash.php" which
     runs on  "" with account "chirico". Assuming you have ssh keys setup, then, the following
     will send mail from the output:

          $ ssh [email protected] "./bin/getslash.php"|mail -s "Slash cron Headlines"  [email protected]

     See (TIP 80) for scraping the headings on slash dot and how to get a copy of "getslash.php".  If you still
     want to use awk:

           $ ssh [email protected] "./bin/getslash.php"| \
                      awk '{ print $0 | "mail -s \x27 Slash Topics \x27 [email protected] "}'

     Note the "\x27" is a quote.  Maybe you only want articles dealing with "Linux":

           $ ssh [email protected] "./bin/getslash.php"| \
                      awk '/Linux/{ print $0 | "mail -s \x27 Slash Topics \x27 [email protected] "}'

     For $60, you can get a numeric display from "delcom engineering" that you can send messages and
     data to.  I get weather information off the internet and send it to this device.

     (Reference TIP 151 for ssh tips)

TIP 52:

     Need to Keep Secrets? Encrypt it.

      To Encrypt:

            $ openssl des3 -salt -in file.txt -out file.des3

      The above will prompt for a password, or you can put it in
      with a -k option, assuming you're on a trusted server.

      To Decrypt

            $  openssl des3 -d -salt -in file.des3 -out file.txt -k mypassword

      Need to encrypt what you type? Enter the following, then start typing
      and  ^D to end.

            $ openssl des3 -salt -out stuff.txt

TIP 53:

     Check that a File has Not Been Tampered With: Use Cryptographic Hashing Function.

     The md5sum is popular but dated

              $ md5sum file

     Instead, use one of the following;

              $ openssl dgst -sha1 -c file

              $ openssl dgst -ripemd160 -c  file

     All calls give a fixed length string or "message digest".

TIP 54:

     Need to View Information About a Secure Web Server? A SSL/TLS test.

           $ openssl s_client -connect

     Above will give a long listing of certificates.

     Note, it is also possible to get certificate information about a mail server

           $ openssl s_client -connect -showcerts

     When you do the above command you get two certificates. If you copy
     past both certificates by taking the following contents include the
     begin and end show below:

                 -----BEGIN CERTIFICATE-----
                 -----END CERTIFICATE-----

     Then create files "comcast0.pem" and "comcast1.pem" out of these certificaties and
     put them in a directory "/home/donkey/.certs", then, with the openssl src package, in
     the "./tools/c_rehash" run

            $ c_rehash .certs
            Doing .certs
            comcast0.pem => 72f90dc0.0
            comcast1.pem => f73e89fd.0

     Now it's possible to have fetchmail work with these certs.

       # Sample .fetchmailrc file for Comcast
       # Check mail every 90 seconds
       set daemon 90
       set syslog
       set postmaster donkey
       #set bouncemail
       # Comcast email is zdonkey but computer account is  just donkey
       poll with proto POP3 and options no dns
              user 'zdonkey' with pass "somethin35"  is 'donkey' here options ssl sslcertck sslcertpath '/home/donkey/.certs'
       # currently not used
       mda '/usr/bin/procmail -d %T'


TIP 55:

     cp --parents. What does this option do?

     Assume you have the following directory structure

            |-- a
            |   `-- b
            |       |-- c
            |       |   `-- d
            |       |       |-- file1
            |       |       `-- file2
            |       `-- x
            |           `-- y
            |               `-- file3
            `-- newdir

     Issue the following command:

         $ cp --parents ./a/b/c/d/* ./newdir/

     Now you have the following:

            |-- a
            |   `-- b
            |       |-- c
            |       |   `-- d
            |       |       |-- file1
            |       |       `-- file2
            |       `-- x
            |           `-- y
            |               `-- file3
            `-- newdir
                `-- a
                    `-- b
                        `-- c
                            `-- d
                                |-- file1
                                `-- file2

     Note that you can't do this with "cp -r" because you'd pickup
     the x directory and its contents. 

     You probably want to use the "cp --parents" command for directory 
     surgery, which you need to be very specific on what you cut and

TIP 56:

     Quickly Locating files.

     The "locate" command quickly searches the indexed database for files.  It just
     gives the name of the files; but, if you need more information use it as follows

         $ locate document|xargs ls -l

     The "locate" database may only get updated every 24 hours.  For more recent finds,
     use the "find" command.

TIP 57:

     Using the "find" Command.

     List only directories, max 2 nodes down that have "net" in the name

       $ find /proc -type d -maxdepth 2 -iname '*net*'

     Find all *.c and *.h files starting from the current "." position.

       $ find . \( -iname '*.c'  -o -iname '*.h' \) -print

     Find all, but skip what's in "/CVS" and "/junk". Start from "/work"

       $ find /work \( -iregex '.*/CVS'  -o -iregex '.*/junk' \)  -prune -o -print

     Note -regex and -iregex work on the directory as well, which means
     you must consider the "./" that comes before all listings.

     Here is another example. Find all files except what is under the CVS, including
     CVS listings. Also exclude "#" and "~".

       $ find . -regex '.*' ! \( -regex '.*CVS.*'  -o -regex '.*[#|~].*' \)

     Find a *.c file, then run grep on it looking for "stdio.h"

       $ find . -iname '*.c' -exec grep -H 'stdio.h' {} \;
         sample output -->  ./prog1.c:#include <stdio.h>
                            ./test.c:#include <stdio.h>

     Looking for the disk-hog on the whole system?

       $ find /  -size +10000k 2>/dev/null

     Looking for files changed in the last 24 hours? Make sure you add the
     minus sign "-1", otherwise, you will only find files changed exactly
     24 hours from now. With the "-1" you get files changed from now to 24

       $ find  . -ctime -1  -printf "%a %f\n"
       Wed Oct  6 12:51:56 2004 .
       Wed Oct  6 12:35:16 2004 How_to_Linux_and_Open_Source.txt

     Or if you just want files.

       $ find . -type f -ctime -1  -printf "%a %f\n"

     Details on file status change in the last 48 hours, current directory. Also note "-atime -2").

       $ find . -ctime -2 -type f -exec ls -l {} \;

             NOTE: if you don't use -type f, you make get "." returned, which
             when run through ls "ls ." may list more than what you want.

             Also you may only want the current directory

       $ find . -ctime -2 -type f -maxdepth 1 -exec ls -l {} \;

     To find files modified within the last 5 to 10 minutes

       $ find . -mmin +5 -mmin -10 

     For more example "find" commands, reference the following looking
     for the latest version of "bashscripts.x.x.x.tar.gz":

     See "TIP 71" for examples of find using the inode feature. " $ find . -inum <inode> -exec rm -- '{}' \; "

     If you don't want error messages, or need to redirect error messages "> /dev/null 2>&1", or see
     "TIP 81".

TIP 58:

     Using the "rm" command.

     How do you remove a file that has the name "-".  For instance, if you run the command
     "$ cat > - " and type some text followed by ^d, how does the "-" file get deleted?

        $ rm -- -

     The "--" nullifies any rm options.

     How do you delete the directory "one", all it's sub-directories, and any data?

        $ rm -rf ./one

     Note, to selectively delete stuff on a directory, use the find command "TIP 57".
     To delete by inode, see "TIP 71".

TIP 59:

     Giving ownership.

     How do you give the user "donkey" ownership to all directories and files under
     "./fordonkey" ?

          $ chown -R donkey ./fordonkey

TIP 60:

     Only Permit root login -- give others a message when they try to login.

     Create the file "/etc/nologin" with "nologin" containing the contents
     of the message.

TIP 61:

     Limits: file size, open files, pipe size, stack size, max memory size
             cpu time, plus others.

     To get a listing of current limits:

          $ ulimit -a
             core file size        (blocks, -c) 0
             data seg size         (kbytes, -d) unlimited
             file size             (blocks, -f) unlimited
             max locked memory     (kbytes, -l) unlimited
             max memory size       (kbytes, -m) unlimited
             open files                    (-n) 1024
             pipe size          (512 bytes, -p) 8
             stack size            (kbytes, -s) 8192
             cpu time             (seconds, -t) unlimited
             max user processes            (-u) 8179
             virtual memory        (kbytes, -v) unlimited

     Note as a user you can decrease your limits in the current
     shell session; but, you cannot increase.  This can be ideal
     for testing programs.  But, first you may want to create
     another shell "sh" so that you can "go back to where started".

          $ ulimit -f 10

     Now try

          $ yes >> out
             File size limit exceeded

     To set limits on users, make changes to "/etc/security/limits.conf"

           bozo   - maxlogins 1

     Will keep bozo from loging in more than once.

     To list hard limits:

          $ ulimit -Ha

     To list soft limits:

          $ ulimit -Sa

     To restrict user access by time, day make changes to

     Also take a look at "/etc/profile" to see what other changes
     can be made, plus take a look under "/etc/security/*.conf" for
     other configuration files.

TIP 62:

     Stupid "cat" Tricks.

     Also see (TIP 43 and TIP 235).

     If you have multiple blank lines that you want to squeeze down to
     one line, then, try the following:

          $ cat -s <file>

     Want to number the lines?

          $ cat -n <file>

     Want to show tabs?

          $ cat -t <file>

     Need to mark end of lines by "$"? The following was suggested by  (Amos Shapira)

          $ cat -e <file>

     Want to see all the ctl characters?

          /* ctlgen.c
            Program to generate ctl characters.


               gcc -o ctlgen ctlgen.c


               ./ctlgen > mout

            Now see the characters:

               cat -v mout

            Here's a sample output:

               $ cat -v mout|tail
                   test M-v
                   test M-w
                   test M-x
                   test M-y
                   test M-z
                   test M-{
                   test M-|
                   test M-}
                   test M-~
                   test M-^?

          #include <stdlib.h>
          #include <stdio.h>
          int main()
            int i;

            for(i=0; i < 256; ++i)
              printf("test %c \n",i);

            return 0;

TIP 63:

     Guard against SYN attacks and "ping".

     As root do the following:

          echo 1 > /proc/sys/net/ipv4/tcp_syncookies

     Want to disable "ping" ?

          echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_all

     Disable broadcast/multicast "ping" ?

          echo 1 > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts

     And to enable again:

          echo 0 > /proc/sys/net/ipv4/icmp_echo_ignore_all

TIP 64:

     Make changes to .bash_profile and need to update the current session?

       $ source .bash_profile

     With the above command, the user does not have to logout.

TIP 65:

     What are the Special Shell Variables?

        $#   The number of arguments.
        [email protected]   All arguments, as separate words.
        $*   All arguments, as one word.
        $$   ID of the current process.
        $?   Exit status of the last command.
        $0,$1,..$9,${10},${11}...${N}    Positional parameters. After "9" you must use the ${k} syntax.

     Note that 0 is true. For example if you execute the following, which is true you get zero.

         $  [[ -f /etc/passwd ]]
         $  echo $?
     And the following is false, which returns a 1.

         $  [[ -f /etc/passwdjabberwisnohere ]]
         $  echo $?

     So true=0 and false=1.

     Sample program "mdo"  to show the difference between "[email protected]" and "$*"

        function myarg
            echo "$# in myarg function"
        echo -e "$# parameters on the cmd line\n"
        echo -e "calling: myarg \"\[email protected]\" and myarg \"\$*\"\n"
        myarg "[email protected]"
        myarg "$*"
        echo -e "\ncalling: myarg \[email protected] and myarg \$* without quotes\n"
        myarg [email protected]
        myarg $*

      The result of running "./mdo one two". Note that when quoted, myarg "$*",
      returns 1 ... all parameters are smushed together as one word.

            [[email protected] theBook]$ ./mdo one two
            2 parameters on the cmd line

            calling: myarg "[email protected]" and myarg "$*"

            2 in myarg function
            1 in myarg function

            calling: myarg [email protected] and myarg $* without quotes

            2 in myarg function
            2 in myarg function

      Example program "mdo2" shows how the input separator can be changed.

        echo -e "$*\n"
        echo -e "$*\n"
        echo -e "$*\n"
        echo -e "$*\n"

            [[email protected] theBook]$ ./mdo2 one two three four five
            one two three four five




TIP 66:

     Replace all "x" with "y" and all "y" with "x" in file data.

        $ cata data
          x y
          y x

        $ tr "xy"  "yx" < data
          y x
          x y

TIP 67:

     On a Linux 2.6.x Kernel, how do you directly measure disk activity,
     and where is this information documented?

          o The information is documented in the kernel source

          o The new way of getting this info in 2.6.x is
              $ cat /sys/block/hda/stat
            151121 5694 1932358 796675 37867 76770 916994 8353762 0 800672 9150437

             Field  1 -- # of reads issued
                 This is the total number of reads completed successfully.
             Field  2 -- # of reads merged, field 6 -- # of writes merged
                 Reads and writes which are adjacent to each other may be merged for
                 efficiency.  Thus two 4K reads may become one 8K read before it is
                 ultimately handed to the disk, and so it will be counted (and queued)
                 as only one I/O.  This field lets you know how often this was done.
             Field  3 -- # of sectors read
                 This is the total number of sectors read successfully.
             Field  4 -- # of milliseconds spent reading
                 This is the total number of milliseconds spent by all reads (as
                 measured from __make_request() to end_that_request_last()).
             Field  5 -- # of writes completed
                 This is the total number of writes completed successfully.
             Field  7 -- # of sectors written
                 This is the total number of sectors written successfully.
             Field  8 -- # of milliseconds spent writing
                 This is the total number of milliseconds spent by all writes (as
                 measured from __make_request() to end_that_request_last()).
             Field  9 -- # of I/Os currently in progress
                 The only field that should go to zero. Incremented as requests are
                 given to appropriate request_queue_t and decremented as they finish.
             Field 10 -- # of milliseconds spent doing I/Os
                 This field is increases so long as field 9 is nonzero.
             Field 11 -- weighted # of milliseconds spent doing I/Os
                 This field is incremented at each I/O start, I/O completion, I/O
                 merge, or read of these stats by the number of I/Os in progress
                 (field 9) times the number of milliseconds spent doing I/O since the
                 last update of this field.  This can provide an easy measure of both
                 I/O completion time and the backlog that may be accumulating.

       Note, this is device specific.

TIP 68:

     Passing Outbound Mail, plus Masquerading User and Hostname.

     Here's a specific example:

         How does one send and receive Comcast email from a home Linux box,
         which uses Comcast as the ISP, if the local account on the Linux
         box is different from the Comcast email.  For instance, the
         account on the Linux box is "[email protected]" and the Comcast
         email account is "[email protected]".  Note both the hostname and
         username are different.

         So, the user "chirico" using "mutt", "elm" or any email program would
         like to send out email to say "[email protected]"; yet, donkey would
         see the email from "[email protected]" and not "[email protected]"
         but [email protected] would get the replies.

         For a full description of how to solve this problem, including related
         "", "site.config.m4", "genericstable", "genericsdomain",
         ".procmailrc", and ".forward" files,  reference the following:


         Included in the above link are instructions for building sendmail with
         "SASL" and "STARTTLS".

TIP 69:

     How do you remove just the last 2 lines from a file and save the result?

         $ sed  '$d' file | sed '$d' > savefile

     Or, as Amos Shapira pointed out, it's much easier with the head command.

         $ head -2 file

      And, of course, removing just the last line

         $ sed '$d' file > savefile

         (See REFERENCES (13))

     How do you remove extra spaces at the end of a line?

         $ sed 's/[ ]*$//g'

     How do you remove blank lines, or lines with just spaces and tabs,
     saving the origional file as file.backup?

         $ perl -pi.backup -e "s/^(\s)*\n//"  file

     Or, you may want to remove empty spaces and tabs at the end of a line

         $ perl -pi.backup -e "s/(\s)*\n/\n/" file

     Or, you may want to converts dates of the format 01/23/2007 to the
     format 2007-01-23. This is MySQL's common date format.

         $ perl -pi.backup -e "s|(\d+)/(\d+)/(\d+)|\$3-\$2-\$1|" file

     Note, you need a backslash \$3,\$2,\$1 so as to not get bash shell

TIP 70:

     Generating Random Numbers.

         $ od -vAn -N4 -tu4 < /dev/urandom

TIP 71:

     Deleting a File by it's Inode Value.

       See (PROGRAMMING TIP 5) for creating the file, or

       $ cat > '\n\n\n\n\n\n\n'
         type some text

     To list the inode and display the characters.

       $ ls -libt *

     To remove by inode. Note the "--" option.  This
     will keep any special characters in the file from being
     interpreted at "rm" options.

       $ find . -inum <inode> -exec rm -- '{}' \;

     Or to check contents

       $ find . -inum <inode> -exec cat '{}' \;


TIP 72:

     Sending Attachments Using Mutt -- On the Command Line.

        $ mutt -s "See Attachment" -a file.doc [email protected] < message.txt

          or just the message:

        $ echo | mutt -a sample.tar.gz [email protected]


        Also see (TIP 51).

TIP 73:

     Want to find out what functions a program calls?

         $ strace <program>

     Try this with "topen.c" (see PROGRAMMING TIP 5)

         $ strace  ./topen

TIP 74:

     RPM Usage Summary.

     Install. Full filename is needed.

         $ rpm -ivh Fedora/RPMS/postgresql-libs-7.4.2-1.i386.rpm

     To view list of files installed with a particular package.

         $ rpm -ql postgresql-libs

     Or, to get the file listing from a package that is not installed use the
     "-p" option.

         $ rpm -pql /iso0/Fedora/RPMS/libpcap-0.8.3-7.i386.rpm

    Note, you can also get specific listing. For example, suppose you
    want to view the changelog

         $ rpm -q --changelog audit
               * Tue Jan 13 2009 Steve Grubb <[email protected]> 1.7.11-2
               - Add crypto event definitions

               * Sat Jan 10 2009 Steve Grubb <[email protected]> 1.7.11-1
               - New upstream release

    Or, maybe you want to see what scripts are installed.

         $ rpm -q --scripts audit
               postinstall scriptlet (using /bin/sh):
               /sbin/chkconfig --add auditd
               preuninstall scriptlet (using /bin/sh):
               if [ $1 -eq 0 ]; then
                    /sbin/service auditd stop > /dev/null 2>&1
                    /sbin/chkconfig --del auditd
               postuninstall scriptlet (using /bin/sh):
               if [ $1 -ge 1 ]; then
                    /sbin/service auditd condrestart > /dev/null 2>&1 || :

     For dependencies listing, use the "R" option.

         $ rpm -qpR /iso0/Fedora/RPMS/libpcap-0.8.3-7.i386.rpm
               kernel >= 2.2.0
               rpmlib(CompressedFileNames) <= 3.0.4-1
               rpmlib(PayloadFilesHavePrefix) <= 4.0-1

     To check the integrity, use the "-K" option.

         $ rpm -K /iso0/Fedora/RPMS/libpcap-0.8.3-7.i386.rpm
               /iso0/Fedora/RPMS/libpcap-0.8.3-7.i386.rpm: (sha1) dsa sha1 md5 gpg OK

     To list all packages installed.

         $ rpm -qa

     To find out which file a package belongs to.

         $ rpm -qf /usr/lib/

     To find the source. (See Tip 246 for more detail)

         $ rpm -qi sysstat

     To uninstall a package

         $ rpm -e

     For building rpm packages reference the following:

     To verify md5 sum so that you know it downloaded ok

         $ rpm -K  *.rpm

     The following is a good reference:

TIP 75:

     Listing Output from a Bash Script.

     Add "set -x"

          set -x

     Will list the files and output as follows:

           + ls
           ChangeLog  CVS  data  test
           + date
           Thu Jul  1 20:41:04 EDT 2004

TIP 76:

     Using wget.

     Grap a webpage and pipe it to less. For example suppose you wanted to pipe the
     contents of all these tips, directly from the web.

      $ wget -O -|less

TIP 77:

     Finding IP address and MAC address.

       $ /sbin/ifconfig

     Note the following output "eth0" and "eth0:1" which means
     two IP addresses are tied to 1 NIC (Network Interface Card).

             eth0      Link encap:Ethernet  HWaddr 00:50:DA:60:5B:AD
                       inet addr:  Bcast:  Mask:
                       UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
                       RX packets:982757 errors:116 dropped:0 overruns:0 frame:116
                       TX packets:439297 errors:0 dropped:0 overruns:0 carrier:0
                       collisions:0 txqueuelen:1000
                       RX bytes:693529078 (661.4 Mb)  TX bytes:78400296 (74.7 Mb)
                       Interrupt:10 Base address:0xa800

             eth0:1    Link encap:Ethernet  HWaddr 00:50:DA:60:5B:AD
                       inet addr:  Bcast:  Mask:
                       UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
                       RX packets:982757 errors:116 dropped:0 overruns:0 frame:116
                       TX packets:439299 errors:0 dropped:0 overruns:0 carrier:0
                       collisions:0 txqueuelen:1000
                       RX bytes:693529078 (661.4 Mb)  TX bytes:78400636 (74.7 Mb)
                       Interrupt:10 Base address:0xa800

             lo        Link encap:Local Loopback
                       inet addr:  Mask:
                       UP LOOPBACK RUNNING  MTU:16436  Metric:1
                       RX packets:785 errors:0 dropped:0 overruns:0 frame:0
                       TX packets:785 errors:0 dropped:0 overruns:0 carrier:0
                       collisions:0 txqueuelen:0
                       RX bytes:2372833 (2.2 Mb)  TX bytes:2372833 (2.2 Mb)

TIP 78:

     DOS to UNIX and UNIX to DOS.

        $ dos2unix file.txt

     And to go the other way from UNIX to DOS

        $ unix2dos unixfile

     See the man page, since there are MAC options.

     NOTE: If you're working file DOS files, you'll probably want to use
           "zip" instead of "gzip" so users on Windows can unzip them.

              $ zip test.txt

TIP 79:

     Need to Run Interactive Commands? Try "expect".

     This simple example waits for the input "hi", in some form before
     returning, immediately, "hello there!". Otherwise, it will wait for
     60 seconds, then, return "hello there!".

          set timeout 60
          expect "hi\n"
          send "hello there!\n"


TIP 80:

     Using PHP as a Command Line Scripting Language.

     The following will grab the complete file from slashdot.

         #!/usr/bin/php -q

         $fileName = "";
         $rss = file($fileName) or die ("Cannot open file $fileName\n");
         for ($index=0; $index < count($rss); $index++)
              echo $rss[$index];

       Note, if you want an example that parses the XML of
       slashdot, then, download the following:


TIP 81:

     Discarding all output -- including stderr messages.

         $ ls  > /dev/null 2>&1

     Or sending all output to a file

         $ someprog > /tmp/file 2>&1

     Sometimes, find displays a lot of errors when searching through
     directories that the user doesn't have access to. To discard
     error messages "stderr", which is normally file descripter "2"
     work the following:

         $ find / -iname 'stuff' 2>/dev/null

          or to pipe results elsewhere

         $ find / -iname 'stuff' > /tmp/results_of_find  2>/dev/null

     Also see (TIP 118).

TIP 82:

     Using MIX.  D. Knuth's  assembly language/machine-code instruction set used in
     his books to illustrate his algorithms.

     Download the source:

       $ ./configure
       $ make
       $ make install

     Documentation can be found at the following link. The link on
     sourceforge is not correct, but, the one below works.

TIP 83:

     Gnuplot [ ].

     This software is ideal for printing graphs.

         gnuplot> set term png
         gnuplot> set output 'testcos.png'
         gnuplot> plot cos(x)*sin(x)
         gnuplot> exit

     Or the following command can be put into "file"

            $ cat > file
            set term png
            set output 'testcos.png'
            plot cos(x)*sin(x)

     Then, run as follows:

            $ gnuplot file

     Or, suppose you have the following file "/home/chirico/data". Comments
     with "#" are not read by gnuplot.

            # File /home/chirico/data
            2005-07-26  1    2.3    3
            2005-07-27  2    3.4    5
            2005-07-28  3    4    6.6
            2005-07-29  4    6    2.5

     And you have the following new "file"

            set term png
            set xdata time
            set timefmt "%Y-%m-%d "
            set format x "%Y/%m/%d"
            set output '/var/www/html/chirico/gnuplot/data.png'
            plot '/home/chirico/data' using 1:2 w linespoints  title '1st col', \
             '/home/chirico/data' using 1:3 w linespoints  title '2nd col', \
             '/home/chirico/data' using 1:4 w linespoints  title '3rd col'

     You can now get a graph of this data running the following:

            $ gnuplot file

TIP 84:

     CPU Information - speed, processor, cache.

            $ cat /proc/cpuinfo

               processor       : 0
               vendor_id       : GenuineIntel
               cpu family      : 15
               model           : 2
               model name      : Intel(R) Pentium(R) 4 CPU 2.20GHz
               stepping        : 9
               cpu MHz         : 2193.221
               cache size      : 512 KB
               fdiv_bug        : no
               hlt_bug         : no
               f00f_bug        : no
               coma_bug        : no
               fpu             : yes
               fpu_exception   : yes
               cpuid level     : 2
               wp              : yes
               flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr
               bogomips        : 4325.37

      "bogomips" is a rough but good way to quickly compare two computer speeds. True it's a
      bogus reading; but, a "good enough" for government work calculation.  See (TIP 10) for
      "vmstat" and "iostat".

TIP 85:

     POVRAY - Making Animated GIFs

     To see this in action, reference:

     These are the basic command to create:

        $ povray orbit.ini -Iorbit.pov
        $ convert -delay 20 *.ppm orbit.gif

     By the way, convert is a program from imagemagick, and it can
     be downloaded from ( ).

    The following is "orbit.pov"

          #include ""
          #include ""
          #include ""
          #include ""
          #include ""
          #include ""

          camera {
            location < 2, 3, -8 >
            look_at  < 0, 0, 0 >
            focal_point <0, 0, 0>
            blur_samples 20

          light_source {
                  < 0, 10, 0>
                  color White
                  area_light <2,0,0>,<0,0,2>, 2, 2
                  adaptive 1
                  fade_distance 8
                  fade_power 1

          sky_sphere {

          plane { <0, 1, 0>, -1
                  texture {
                          pigment {
                                  checker color Blue, color White
                          finish {Phong_Glossy}
          #declare ball0=
                  sphere {
                  <0.5, 0.5, 0>, 1
                  texture {
                  pigment {Yellow}

          #declare ball1=
                  sphere {
                  <3, 2, 0>, 0.5
                  texture {
                  pigment {Blue}

          #declare ball2=
                  sphere {
                  <3, 1, 0>, 1
                  texture {
                  pigment {Green}

          object {ball0 rotate 360*clock*y}
          object {ball1 rotate 720*clock*y}
          object {ball2 rotate 360*(1 - clock)*y}

    And, "orbit.ini" follows:






TIP 86:

     GPG --  GnuPG

                   (SCRIPT 4) on following link:

     Generage key:

        $ gpg --gen-key

     Generate public key ID and fingerprint

        $ gpg --fingerprint

     Get a list of keys:

        $ gpg --list-keys

          pub  1024D/A11C1499 2004-07-15 Mike Chirico <[email protected]>
          sub  1024g/E1A3C2B3 2004-07-15


        $ gpg -r Mike  --encrypt sample.txt

       This will produce "sample.txt.asc", which is a binary file.  Note, I can use "Mike" because that's the
       name on the list of keys. Again, it will be a binary file.

     Encrypt using "ASCII-armored text"  (--armor), which is probably what you want when sending "in" the body of an
     email, or some document.

        $ gpg  -r Mike  --encrypt --armor sample.txt
        $ gpg -r Mike -e -a sample.txt
        $ gpg --output somefile.asc --armor -r Mike  --encrypt --armor sample.txt

     The above 3 statements will still produce "sample.txt.asc", but look at it, or "$ cat sample.txt.asc" without 
     fear, since there are no binary characters. Yes, you could even compile a program "$ g++ -o test test.c" , then,
     "$ gpg --output test.asc  -r Mike --encrypt --armor test". However, when decrypting make sure to pipe
     the results.

            $ gpg --decrypt test.asc > test

     Export "public" key:

           $ gpg --armor --export Mike > m1.asc

     Signing the file "message.txt":

           $ gpg --clearsign message.txt

     Sending the key to the "key-server"

        First, list the keys.

                $ gpg --list-keys
                                 v------------------ Use this with "0x" in front -------
                  pub  1024D/A11C1499 2004-07-15 Mike Chirico  <[email protected]>   |
                  sub  1024g/E1A3C2B3 2004-07-15                                        |
                $ gpg --send-keys 0xA11C1499

             The above sends it to the keyserver defined in "/home/chirico/.gnupg/gpg.conf".  Other key servers:


             When you go to your user-group meetings, you need to bring 2 forms of ID, and
             list your Key fingerprint. Shown below is the command for getting this fingerprint.

                $ gpg --fingerprint [email protected]
                 pub   1024D/A11C1499 2004-07-15
                 Key fingerprint = 9D7F C80D BB7B 4BAB CCA4  1BE9 9056 5BEC A11C 1499
                 uid   Mike Chirico ( <[email protected]>
                 sub   1024g/E1A3C2B3 2004-07-15

     Receving keys:

        The following will retrieve my [email protected] key

               $ gpg --recv-keys 0xA11C1499

     Special Note: If you get the following error "GPG: Warning: Using Insecure Memory" , then,
                   " chmod 4755 /path/to/gpg"  to setuid(root) permissioins on the gpg binary.

     NOTE: If using mutt, just before sending with the "y" option, hit "p" to sign or encrypt.

     It's possible to create a gpg/pgp email from the command line. For a tutorial on this,
     reference (SCRIPT 4) at the following link:

TIP 87:

     Working with Dates: Steffen Beyer has developed a Perl and C module for working with dates

     This softare can be downloaded from the following location:

         $ wget
         $ tar -xzvf Date-Calc-5.3.tar.gz
         $ cd Date-Calc-5.3
         $ cp ./examples/cal.c .
         $ gcc cal.c DateCalc.c -o mcal

     The file cal.c contains sample function calls from DateCalc.c.  Note, "DateCalc.c"
     is just a list of functions and includes for "DateCalc.h" and "ToolBox.h".

     Or, and this may be easier, just download the following:

     The above link contains a few examples.

TIP 88:

     Color patterns for mutt.

     The colors can be changed in the /home/user/.muttrc file. The first field begins with
     color, the second field is the foreground color, and the third field is the background
     color, or default.

     An example .muttrc for colors:

       # color patterns for mutt
       color normal     white          black # normal text
       color indicator  black          yellow  # actual message
       color tree       brightmagenta  default # thread arrows
       color status     brightyellow         default # status line
       color error      brightred      default # errors
       color message    magenta        default # info messages
       color signature  magenta        default # signature
       color attachment brightyellow   red     # MIME attachments
       color search     brightyellow   red     # search matches
       color tilde      brightmagenta  default # ~ at bottom of msg
       color markers    red            default # + at beginning of wrapped lines
       color hdrdefault cyan           default # default header lines
       color bold       red            default # hiliting bold patterns in body
       color underline  green          default # hiliting underlined patterns in body
       color quoted     cyan           default # quoted text
       color quoted1    magenta        default
       color quoted2    red            default
       color quoted3    green          default
       color quoted4    magenta           default
       color quoted5    cyan           default
       color quoted6    magenta        default
       color quoted7    red            default
       color quoted8    green          default
       color quoted9    cyan           default
       color body   cyan  default  "((ftp|http|https)://|news:)[^ >)\"\t]+"
       color body   cyan  default  "[-a-z_0-9.+][email protected][-a-z_0-9.]+"
       color body   red   default  "(^| )\\*[-a-z0-9*]+\\*[,.?]?[ \n]"
       color body   green default  "(^| )_[-a-z0-9_]+_[,.?]?[\n]"
       color body   red   default  "(^| )\\*[-a-z0-9*]+\\*[,.?]?[ \n]"
       color body   green default  "(^| )_[-a-z0-9_]+_[,.?]?[ \n]"
       color index  cyan  default  ~F         # Flagged
       color index  red   default  ~N         # New
       color index  magenta    default  ~T         # Tagged
       color index  cyan       default  ~D         # Deleted

     Also see (TIP 190)

TIP 89:

     ps command in detail

     Here are the possible codes when using state "$ ps -e -o state,cmd"

                  D   uninterruptible sleep (usually IO)
                  R   runnable (on run queue)
                  S   sleeping
                  T   traced or stopped
                  Z   a defunct ("zombie") process

                  <    high-priority (not nice to other users)
                  N    low-priority (nice to other users)
                  L    has pages locked into memory (for real-time and custom IO)
                  s    is a session leader
                  l    is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
                  +    is in the foreground process group

    For instance:

     Note that the -o is for user defined, and -e is for select
     all process.

       $ ps -e -o pid,state,start,time,etime,cmd

             9946 S 15:40:45 00:00:00    02:23:29 /bin/bash -i
             9985 T 15:41:24 00:00:01    02:22:50 emacs mout2
            10003 T 15:43:59 00:00:00    02:20:15 emacs NOTES
            10320 T 17:38:42 00:00:00       25:32 emacs stuff.c

     You may want to command below, without the -e, which will give the
     process only under the current terminal.

       $ ps -o pid,state,start,time,etime,cmd

     Want to find what 's impacting your load?

       $ ps -e -o %cpu,pid,state,start,time,etime,%cpu,%mem,cmd|sort -rn|less

       $ ps aux

            root         1  0.0  0.0  1380  480 ?        S    Aug04   0:00 init [3]
            root         2  0.0  0.0     0    0 ?        SWN  Aug04   0:00 [ksoftirqd/0]
            root         3  0.0  0.0     0    0 ?        SW<  Aug04   0:00 [events/0]
            root         4  0.0  0.0     0    0 ?        SW<  Aug04   0:00 [khelper]

     Or, if you want to see the environment add the -e option

       $ ps aeux

            chirico   2735  0.0  0.1  4400 1492 pts/0    S    Aug04   0:00 -bash USER=chirico LOGNAME=chirico HOME=/home/chirico PATH=/usr/
            chirico   2771  0.0  0.0  4328  924 pts/0    S    Aug04   0:00 screen -e^Pa -D -R HOSTNAME=third-fl-71.localdomain TERM=xterm S
            chirico   2772  0.0  0.6  9476 6352 ?        S    Aug04   0:54 SCREEN -e^Pa -D -R HOSTNAME=third-fl-71.localdomain TERM=xterm S
            chirico   2773  0.0  0.1  4432 1548 pts/1    S    Aug04   0:10 /bin/bash STY=2772.pts-0.third-fl-71 TERM=screen TERMCAP=SC|scre
            chirico   2797  0.0  0.1  4416 1496 pts/2    S    Aug04   0:00 /bin/bash STY=2772.pts-0.third-fl-71 TERM=screen TERMCAP=SC|scre
            root      2821  0.0  0.0  4100  952 pts/2    S    Aug04   0:00 su -
            root      2822  0.0  0.1  4384 1480 pts/2    S    Aug04   0:00 -bash
            chirico   2862  0.0  0.1  4428 1524 pts/3    S    Aug04   0:00 /bin/bash STY=2772.pts-0.third-fl-71 TERM=screen TERMCAP=SC|scre
            sporkey   2946  0.0  0.2  6836 2960 ?        S    Aug04   0:15 fetchmail
            chirico   2952  0.0  0.1  4436 1552 pts/5    S    Aug04   0:00 /bin/bash STY=2772.pts-0.third-fl-71 TERM=screen TERMCAP=SC|scre
            chirico   3880  0.0  0.1  4416 1496 pts/6    S    Aug05   0:00 /bin/bash STY=2772.pts-0.third-fl-71 TERM=screen TERMCAP=SC|scre
            root      3904  0.0  0.0  4100  956 pts/6    S    Aug05   0:00 su - donkey
            donkey    3905  0.0  0.1  4336 1452 pts/6    S    Aug05   0:00 -bash
            donkey    3938  0.0  0.2  6732 2856 ?        S    Aug05   0:14 fetchmail
            chirico   3944  0.0  0.1  4416 1496 pts/7    S    Aug05   0:00 /bin/bash STY=2772.pts-0.third-fl-71 TERM=screen TERMCAP=SC|scre

     There is also a -f "forrest" option. Also note below " -bash" is the start of a login shell.

      $ ps aeuxwwf 

     The ww option above gives a wide format with all variables. Use the above command if you plan
     to parse through a Perl script. Otherwise, it may be easier to do a quick read using the command
     below, without "ww".    

      $ ps aeuxf

            root      2339  0.0  0.1  3512 1444 ?        S    Dec01   0:00 /usr/sbin/sshd
            root     25651  0.0  0.1  6764 1980 ?        S    Dec23   0:00  \_ /usr/sbin/sshd
            chirico  25653  0.0  0.2  6840 2236 ?        S    Dec23   0:14      \_ /usr/sbin/sshd
            chirico  25654  0.0  0.1  4364 1440 pts/4    S    Dec23   0:00          \_ -bash USER=chirico LOGNAME=chirico HOME=/home/chirico
            chirico  25690  0.0  0.0  4328  920 pts/4    S    Dec23   0:00              \_ screen -e^Pa -D -R HOSTNAME=third-fl-71.localdomain TERM=xterm
            root      2355  0.0  0.0  2068  904 ?        S    Dec01   0:00 xinetd -stayalive -pidfile /var/run/

     It is also possible to list the process by command line. For example, the following command will only list the emacs

      $ ps -fC emacs
       UID        PID  PPID  C STIME TTY          TIME CMD
       chirico   5049  5020  0 May11 pts/13   00:00:00 emacs -nw Notes
       chirico  12368  5104  0 May12 pts/18   00:00:00 emacs -nw dnotify.c
       chirico  19792 18028  0 May13 pts/20   00:00:00 emacs -nw hello.c
       chirico  14034 27367  0 18:52 pts/8    00:00:00 emacs -nw How_to_Linux_and_Open_Source.txt

     You may also want to consider using top in batch mode. Here the "-n 1" means refresh once,
     and the "b" is for batch. The "fmt -s" is to put it in a more readable format.

       $ top -n 1 b |fmt  -s >>statfile

TIP 90:

     Learning Assembly.

     Once you have written the source, assuming the file is "exit.s", it can be compiled as follows:

            $ as exit.s -o exit.o
            $ ld exit.o -o exit

     Here is the program:

         #INPUT:  none
         #OUTPUT:         returns a status code. This can be viewed
         # by typing
         # echo $?
         # after running the program
         # %eax holds the system call number
         # (this is always the case)
         # %ebx holds the return status
                 .section .data
                 .section .text

                 .globl _start
                 movl $1, %eax # this is the linux kernel command
                 # number (system call) for exiting
                 # a program
                 movl $0, %ebx # this is the status number we will
                 # return to the operating system.
                 # Change this around and it will
                 # return different things to
                 # echo $?
                 int $0x80 # this wakes up the kernel to run
                 # the exit command

     After running this program, you can get the exit code.

            $ echo $?

     That is about all it does; but, get the book for more details. The
     book is free.

TIP 91:

     Creating a sandbox for reiserfstune,debugreiserfs and ACL.  Also see TIP 4.

     Assume you have a reisers files system created from a disk file, which
     means you have done something like the following:

          # dd if=/dev/zero of=disk-rfs count=102400
          # losetup  /dev/loop4 ./disk-rfs
          # mkfs -t reiserfs /dev/loop4
          # mkdir /fs2
          # mount -o loop,acl ./disk-rfs /fs2

     Now, you can run reiserfstune. But, first you will need to umount fs2

          # umount /fs2
          # reiserfstune ./disk-rfs

     Or you can run the debug command

          # debugreiserfs -J ./disk-rfs

     Now, suppose you run through a lot of the debug options on and you destroy this file.

     You can recreate the file and delete the loop device.

          # dd if=/dev/zero of=disk-rfs count=102400
          # losetup -d /dev/loop4
          # mount -o loop,acl ./disk-rfs /fs2

     Now, try working with some of the ACL options - you can only do this
     with the latest kernel and tools -- Fedora Core 2 will work.

     Assume you have 3 users, donkey, chirico and bozo2. You can give
     everyone rights to this file system as follows:

          # setfacl -R -m d:u:donkey:rwx,d:u:chirico:rwx,d:u:bozo2:rwx /fs2

TIP 92:

     SpamAssassin - Setup.

     Step 1.

           Installing the SpamAssassin CPAN utility. You will need to do this
           as root.

              $ su -

           Once you have root privileges invoke cpan.

              # perl -MCPAN -e shell


           Now install with prerequisites policy set to ask.

              cpan> o conf prerequisites_policy ask

              cpan> install Mail::SpamAssassin

           You will get lots of output as the necessary modules are downloaded and
           compiled and installed.

     Step 2.


            Edit the following "/etc/mail/spamassassin/"

            Here is a look at my file

                $ cat /etc/mail/spamassassin/

                # This is the right place to customize your installation of SpamAssassin.
                # See 'perldoc Mail::SpamAssassin::Conf' for details of what can be
                # tweaked.
                # rewrite_subject 0
                # report_safe 1
                # trusted_networks 212.17.35.

                # Below added from book
                # You may want to set this to 5, then, work your way down.
                # Currently I have this 3
                required_hits 3

                # This determines how spam is reported. Currently safe email is reported
                # in the message.
                report_safe 1

                # The will rewrite the tag of the spam message.
                rewrite_subject 1

                # By default, SpamAssassin will run RBL checks.  If your ISP already
                # does this, set this to 1.
                skip_rbl_checks 0

     Step 3.

            Update .procmail.

            You should update the .procmail file as follows. Here is my /home/chirico/.procmail file.

                $ cat /home/chirico/.procmailrc

                #  Must have folder MailTRASH

                # Will get everything from this mail
                * ^From:.*[email protected]

                # Spamassassin
                * <300000


TIP 93:

     Make Graphs: using dot and neato.

       $ dot -Tpng dotfile -o myout.png

     To see the output reference the following:

     Where "dotfile" is the following:

       $ cat dotfile

       digraph g
               node [shape = record];

               node0 [ label ="<f0> stuff | <f1> J | <f2> "];
               node1 [ label ="<f0> | <f1> E | <f2> "];
               node4 [ label ="<f0> | <f1> C | <f2> "];
               node6 [ label ="<f0> | <f1> I | <f2> "];
               node2 [ label ="<f0> | <f1> U | <f2> "];
               node5 [ label ="<f0> | <f1> N | <f2> "];
               node9 [ label ="<f0> | <f1> Y | <f2> "];
               node8 [ label ="<f0> | <f1> W | <f2> "];
               node10 [ label ="<f0> | <f1> Z | <f2> "];
               node7 [ label ="<f0> | <f1> A | <f2> "];
               node3 [ label ="<f0> | <f1> G | <f2> "];

               "node0":f0 -> "node1":f1;
               "node0":f2 -> "node2":f1;

               "node1":f0 -> "node4":f1;
               "node1":f2 -> "node6":f1;
               "node4":f0 -> "node7":f1;
               "node4":f2 -> "node3":f1;

               "node2":f0 -> "node5":f1;
               "node2":f2 -> "node9":f1;

               "node9":f0 -> "node8":f1;
               "node9":f2 -> "node10":f1;

     Checkout the following article:

     To download this software

TIP 94:

     Makefile: working with conditions

     First note that all the indentations of the file must be
     a single tab. There cannot be any spaces, or make will
     not run.

       $ cat Makefile

        # Compiler flags
        sqliteLIB := $(shell ls /usr/local/lib/
        sqlite3LIB := $(shell ls /usr/local/lib/
        # all assumes sqlite and sqlite3 are installed

        ifeq ("$(sqlite3LIB)","/usr/local/lib/")
             @echo -e "True -- we found the file"
             @echo "False -- we did not find the file"

     So, if I run make I will get the following output.

       $ make
       True -- we found the file

     This is because I have a file /usr/local/lib/ on my system.
     Note how the assignment is made, with the shell command

           sqlite3LIB := $(shell ls /usr/local/lib/

TIP 95:

     Bash: Conditional Expressions

          if [ -e /etc/ntp.conf ]
              echo "You have the ntp config file"
              echo "You do not have the ntp config file"

       Now using an AND condition inside the [ ]. By the way, above, you
       can put the "then" on the same line as the if "if [ -e /etc/ntp.conf ]; then"
       as long as you use the ";".

           if [ \( -e /etc/ntp.conf \) -a \( -e /etc/ntp/ntpservers \) ]
               echo "You have ntp config and ntpservers"
             elif [ -e /etc/ntp.conf ]; then
               echo " You just have ntp.conf "
             elif [ -e /etc/ntp/ntpservers ]; then
               echo " You just have ntpservers "
               echo " you have neither ntp.conf or ntpservers"

        A few things to note above. Else if statement is written as "elif", and when
        dealing with "(" you will need to insert "\(". By the way "-o" can replace "-a"
        and the "-o" is for OR condition. AND can be done as follows too.

           if [ -e /etc/ntp.conf ] && [ -e /etc/ntp/ntpservers ]
               echo "You have ntp config and ntpservers"
             elif [ -e /etc/ntp.conf ]; then
               echo " You just have ntp.conf "
             elif [ -e /etc/ntp/ntpservers ]; then
               echo " You just have ntpservers "
               echo " you have neither ntp.conf or ntpservers"

          Conditional Expressions (files).

             -b file      True if file exists and is a block file
             -c file      True if file exists and is a character device file
             -d file      True if file exists and is a directory
             -e file      True if file exists
             -f file      True if file exists and is a regular file
             -g file      True if file exists and is set goup id
             -G file      True if owned by the effective group ID

             -k file      True if "sticky" bit is set and file exists
             -L file      True if file exists and is a symbolic link
             -n string    True if string is non-null

             -O file      Ture if file exists and is owned by the effective user ID

             -p file      True if file is a named pipe (FIFO)
             -r file      True if file is readable
             -s file      True if file has size > 0
             -S file      True if file exists and is a socket

             -t file      True if file is open and refers to a terminal.
             -u file      True if setuid bit is set
             -w file      True if file exists and is writeable
             -x file      True if file executable
             -x dir       True if directory can be searched

             file1 -nt file2     True if file1 modification date newer than file2
             file1 -ot file2     True if file1 modification date older than file2
             file1 -ef file2     True if file1 and file2 have same inode

          Conditional Expressions (Integers).

             -lt  Less than
             -le  Less than or equal
             -eq  Equal
             -ge  Greater than or equal
             -gt  Greater than
             -ne  Not equal

          Example usage.

               while read num value; do
                if [ $num -gt  2 ]; then
                  echo $value
             } < somefile

          Conditional Expressions (Strings).

             str1 = str2      str1 matches str2
             str1 != str2     str1 does not matches str2
             str1 < str2      str1 is less than str2
             str1 >  str2     str1 is greater than str2
             -n str1          str1 is not null (length greater than 0)
             -z str1          str1 is null (las length 0)

TIP 96:

     CVS: Working with cvs


       To create a repository, and this is normally done by the system admin. This
       is NOT creating a project to checkout, but the location where everything
       will be stored! The initial repository!

             cvs -d repository_root_directory init

       Or here is a specific example:

             cvs -d /work/cvsREPOSITORY/   init

       Creating a directory tree from scratch. For a new project, the easiest thing to
       do is probably to create an empty directory structure, like this:

             $ mkdir sqlite_examples
             $ mkdir sqlite_examples/man
             $ mkdir sqlite_examples/testing

       After that, you use the import command to create the
       corresponding (empty) directory structure inside the repository:

             $ cd <directory>
             $ cvs -d repository_root_directory import  -m "Created directory structure" yoyodyne/dir yoyo start

       Or, here is a specific example.

             $  cd sqlite_examples
             $  cvs  -d /work/cvsREPOSITORY/ import -m 'test SQlite'  sqlite_examples sqlite_examples start

       Now, you can delete the directory sqlite_examples, or go to another directory and type
       the following:

             $ cvs -d /work/cvsREPOSITORY/ co sqlite_examples


           1. cvsps
           2. cvsreport

         cvsps which you can find at

             $ cvsps -f README_sqlite_tutorial.html

TIP 97:

     Common vi and vim commands

           Command mode ESC

                dd       delete
                u        undelete
                y        yank (copy to buffer)
                p/P      p before cursor/P after cursor

                Ctl-g    show current line number
                shft-G   end of file
              n shft-G   move to line n

               /stuff/   search
                  n   repeat in same direction
                  N   repeat in opposite direction
                  /return  repeat seach forward
                  ?return  repeat seach backward

               "dyy  Yank current line to buffer d
               "a7yy Yank next 7 lines to buffer a
               :1,7ya a  Yank [ya] lines 1,7 to buffer a
               :1,7ya b  Yank [ya] lines 1,7 to buffer b

               :5 pu b   Put [pu] buffer b after line 5

               "dP   Put the content of buffer d before cursor
               "ap   Put the contents of buffer a after cursor

               :1,4 w! file2  Write lines 1,4 to file2

               :set nu     Display line numbers
               :set nonum  Turns off display

               :set ic     Ignore Case

               :e <filename> Edit a file in a new buffer

               :g/<reg exp>/p   Print matching regular expression

               :split <filename>
               :sp <filename>
               :split new

                   ctl-w   To move between windows
                   ctl-w-  To change size
                   ctl+wv  Split windows vertically
                   ctl-wq  Close window

               :only       To view only 1 window

            vim dictionary - put the following command in ~/.vimrc

                   set dictionary+=/usr/share/dict/words
                   set thesaurus+=/usr/share/dict/words

               Now, after you type a word <ctl-x><ctl-k><ctl-n> and to 
               go back in the listing <ctl-p>


           Scripting - you can script vi commands using ex. For example
               suppose you want to replace all occurrences of "one" with "two", then
               exit the file if there are changes. You would put the following in a file call script

               Contents of script


               If you want to run this on all files with the patten "example*"

                   for i in $(ls example*); do ex - $i <script; done

TIP 98:

     Using apt-get

          $ apt-get update
          $ apt-get -s install <pkage>    <---- if everything is ok, then, remove the s

     Note you may want to use dpkg to purge if you have to do a reinstall.

          $ dpkg --purge exim4-base
          $ dpkg --purge exim4-config
          $ apt-get install exim4

          $ dpkg-reconfigure exim4-config

TIP 99:

     Mounting a cdrom on openbsd and installing packages

          $ mkdir -p /cdrom
          $ mount /dev/cd0a /cdrom
          $ cd /cdrom

     To add packages

          $ pkg_add -v  <directory>

     Mounting a cdrom on linux to a user's home sub-directory:

          $ mkdir -p /home/chirico/cdrom
          $ mount /dev/cdrom /home/chirico/cdrom

TIP 100:

    Creating a boot floppy for knoppix cd:

          $ dd if=/mnt/cdrom/KNOPPIX/boot.img of=/dev/fd0 bs=1440k


    For a lot of the knoppix how-to's

TIP 101:

    Diction and Style Tools for Linux

        $ diction mytext|less

    Or, this can be done interactively

        $ diction
        This is more text to read and you can do with it
        what you want.
        (stdin):1: This is more text to read and you [can -> (do not confuse with "may")] do with it what you want.

       Diction finds all sentences in a document, that contain phrases from  a
       database  of  frequently  misused,  bad  or  wordy diction.  It further
       checks for double words.  If no files are given, the document  is  read
       from  standard input.  Each found phrase is enclosed in [ ] (brackets).
       Suggestions and advice, if any, are printed headed by a right arrow ->.
       A  sentence is a sequence of words, that starts with a capitalised word
       and ends with a full stop, double colon, question mark or  exclaimation
       mark.  A single letter followed by a dot is considered an abbreviation,
       so it does not terminate a sentence.   Various  multi-letter  abbrevia-
       tions are recognized, they do not terminate a sentence as well.

TIP 102:

    Using a mail alias.

       Suppose all root mail on your system to go to one root account [email protected]

       In the following file:


       Add this line

             root:    [email protected]

       Next, run newaliases [/usr/bin/newaliases] as follows:

             $ newaliases

       Special note: It's possible to send mail to more than one address. Suppose you want
                     mail going to [email protected] above, plus you want it going to user donkey
                     on the local system.

             root:  [email protected] donkey

TIP 103:

    Chrony - this service is similiar to ntp. It keeps accurate time
            on your computer against a very accurate clock in across
            a network with various time delays.


        In the file "/etc/chrony/chrony.conf" add/replace the following


        Next start the chrony service

           $ /etc/init.d/chrony restart

     Next verify that this is working. It may take 20 or 30 minutes to update
     the clock.

     Shell command:
       # chronyc
       chronyc> sourcestats
       210 Number of sources = 3
       Name/IP Address            NP  NR  Span  Frequency   Freq Skew   Std Dev
       ========================================================================            2   0    64       0.000    2000.000  4000ms                2   0    66       0.000    2000.000  4000ms
       FS3.ECE.CMU.EDU             2   0    64       0.000    2000.000  4000ms

    It is probably best to let chrony do its work. However, if you want to
    set both the hardware and software clock, the following will work:

      Sets the hardware clock
        # hwclock --set --date="12/10/04 10:18:05"

      Sync the hardware clock to software
        # hwclock --hctosys

      Set the timezone
        # ln -sf /usr/share/zoneinfo/UTC /etc/localtime
        # ln -sf /usr/share/zoneinfo/US/Eastern /etc/localtime

      Set ZONE in /etc/sysconfig/clock


       or I use the following for my timezone 

          ZONE="America/New York"

    Normally the system keep accurate time with the software clock.

TIP 104:

    NFS mount

     SERVER (

       Make sure nfs is running on the server

           $ /etc/init.d/nfs restart

       At the server the contents of /etc/exports for
       allowing 2 computers ( and
       to access the home directory of this server. Note that
       read write (rw) access is allowed.

          $ cat /etc/exports

       Or, if you have a lot of clients on 192.168.1.* then consider
       the following:


       Next, still at the server, run the exportfs command

          $ exportfs -rv

       IPTABLES (lokkit). If you're using fedora with default lokkit firewall
                then you can put the following under "Other ports".

                  Other ports nfs:tcp nfs:udp

       If the above does not work or you are not using lokkit
        IPTABLES (values in /etc/sysconfig/iptables on SERVER )

        # NFS Need to accept fragmented packets and may not have header
        #             so you will not know where they are coming from
        -A INPUT -f -j ACCEPT
        -A INPUT -p tcp -m tcp -s -m multiport --dports 111,683,686,685,1026,2049,2219  -j ACCEPT
        -A INPUT -p tcp -s -d 0/0 --dport 32765:32768  -j ACCEPT
        -A INPUT -p udp -m udp -s -m multiport --dports 111,683,686,685,1026,2049,2219  -j ACCEPT
        -A INPUT -p udp -s -d 0/0 --dport 32765:32768  -j ACCEPT

        -A INPUT -f -j ACCEPT
        -A INPUT -p tcp -m tcp -s -m multiport --dports 111,683,686,685,1026,2049,2219  -j ACCEPT
        -A INPUT -p tcp -s -d 0/0 --dport 32765:32768  -j ACCEPT
        -A INPUT -p udp -m udp -s -m multiport --dports 111,683,686,685,1026,2049,2219  -j ACCEPT
        -A INPUT -p udp -s -d 0/0 --dport 32765:32768  -j ACCEPT


     CLIENT1 (

          $ mkdir -p /home2

          $ cat /etc/fstab          /home2     nfs     rw 0 0

          $ mount -a -t nfs

        Or to do a one time mounting by hand

          $ mount -t nfs  /home2

        Now /home2 on the client will be /home on the server



        To monitor the client:

          $ nfsstat -c

           Also note you can "cat /proc/net/rpc/nfs" as well.

       To monitor the server (note the -s instead of the -c).

         $ nfsstat -s

           Also note you can "cat /proc/net/rpc/nfsd" as well.

       The following "cat" command is done on the NFS server, and shows which
       clients are mounting. This does not go with examples above. By the way,
       "root_squash" is the default, and means that root access on the clients is
       denied. So, how does the client root get access to these filesystems? You have
       to "su - <someuser>".

              $ cat /proc/fs/nfs/exports
              # Version 1.1
              # Path Client(Flags) # IPs

     (Reference: )

TIP 105:

      Ports used for Microsoft products

      To find out common port mappings, take a look at "/etc/services"

      To find an extensive list, reference

TIP 106:

      Man pages: If man pages are formatting incorrectly with PuTTY, try editing
      the "/etc/man.config" file with the following changes:

           NROFF /usr/bin/groff -Tlatin1 -mandoc
           NEQN /usr/bin/geqn -Tlatin1

         (Reference TIP 7 for using man)

TIP 107:

      Valgrind: check for memory leaks in your programs. (

       This is how you can run it on the program "a.out" for valgrind version 2.2.0

         $ valgrind --logfile=valgrind.output   --tool=memcheck ./a.out

       This is how you write the logfile "--log-file" for valgrind-3.0.1

         $ valgrind  --log-file=valgrind --leak-check=yes --tool=memcheck ./a.out

       With C++ programs with gcc 3.4 and later that use STL, export GLIBCXX_FORCE_NEW 
       only when testing to disable memory caching. Remember to enable for production
       as this will have a performance penalty. Reference 

TIP 108:

      Runlevel Configuring.

       The program ntsysv, run as root, gives you a ncurses GUI to what will
       run on your system on boot. The chkconfig program (man chkconfig) has
       the ability to list which programs are set to start on the chosen 
       run level.

            # ntsysv

            # chkconfig 

       If at this moment you want to see what services are currently running,
       then, run the following command:

            # /sbin/service --status-all

       Note, you can also set these manually. For example, normally you will
       have files in "/etc/init.d/" that will take parameters like "start","stop"

       Take a look at "/etc/init.d/mysql" this file will start and stop the
       mysql daemon. So, how does know which run levels, and the order it gets
       loaded in the run level to other programs? By the K<number> and S<number>

            $ ls /etc/rc3.d/*mysql


       So here on my system the start value is 85. Looking in /etc/rc3.d, which is
       run level 3, any program with a lower number S84something will get loaded
       before mysql.

       I manually set the run level as follows for mysql.

            # cd /etc/rc3.d
            # ln -s ../init.d/mysql S85mysql
            # ln -s ../init.d/mysql K85mysql

            # cd /etc/rc5.d
            # ln -s ../init.d/mysql S85mysql
            # ln -s ../init.d/mysql K85mysql

       Note that I could have chose other numbers as well. "ntsysv" gives
       you a graphical interface.

       This is a way of doing this with "chkconfig" at the command prompt.

            # chkconfig --list mysqld
            mysqld          0:off   1:off   2:off   3:on    4:off   5:on    6:off

       Above you can see it's on. Here's how we would have turned this on with chkconfig.

            # chkconfig --level 35 mysqld on


TIP 109:

       File Alteration Monitor - Gamin a FAM replacement
       ******  EXAMPLE NOT COMPLETE *****

       Working with fam  - file alteration monitor.  Mail uses this to signify
           a change in a file's status.

        Below is the sample C program ftest.c which can be compiled as

              $ gcc -o ftest ftest.c  -lfam

        You will need to work with this as root

              #  ./ftest <somefile absolute path>


TIP 110:

       glibc - this is the main library used by C, and the following
        link below gives you examples on everything from sockets,math,
        date and time functions, user environment, and much more.

       How do you know which version of glibc you are running?

          #include <stdio.h>
          #include <gnu/libc-version.h>
          int main (void)
             puts (gnu_get_libc_version ());
             return 0;

	Thanks to Jorg Esser for pointing this out, there is a
	way to get the GNU C library version directly, by running
        the library name as if it were a command line.

	[[email protected] ~]$ /lib/

	GNU C Library stable release version 2.7, by Roland McGrath et al.
	Copyright (C) 2007 Free Software Foundation, Inc.
	This is free software; see the source for copying conditions.
	There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
	Compiled by GNU CC version 4.1.2 20070925 (Red Hat 4.1.2-32).
	Compiled on a Linux >>2.6.20-1.3001.fc6xen<< system on 2007-10-18.
	Available extensions:
		The C stubs add-on version 2.1.2.
		crypt add-on version 2.1 by Michael Glad and others
		GNU Libidn by Simon Josefsson
		Native POSIX Threads Library by Ulrich Drepper et al
		RT using linux kernel aio
		For bug reporting instructions, please see:

TIP 111:

       nslookup and dig - query Internet name servers interactively.

         $ nslookup


      The nslookup command will query the dns server is "/etc/resolve.conf"
      However, you can force a certain dns with "- server".  For example the
      command below goes to the server named dilbert

         $ nslookup - dilbert


      dig gives you more information. You should probably use dig instead
      of nslookup.

      Below I am forcing the lookup from DNS of the name, and
      note that the query time is return too.

         $ dig @  +qr

         ; <<>> DiG 9.2.1 <<>> @ +qr
         ;; global options:  printcmd
         ;; Sending:
         ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55908
         ;; flags: rd; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

         ;                   IN      A

         ;; Got answer:
         ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 55908
         ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2

         ;                   IN      A

         ;; ANSWER SECTION:            5538    IN      A

         ;; AUTHORITY SECTION:            30599   IN      NS            30599   IN      NS

         ;; ADDITIONAL SECTION:      16022   IN      A      7       IN      A

         ;; Query time: 155 msec
         ;; SERVER:
         ;; WHEN: Thu Dec 23 07:48:23 2004
         ;; MSG SIZE  rcvd: 127

      So what if you wanted to know what name the IP address
      resolves to, when using dns

          $ dig @ -x
          ;; ANSWER SECTION:
 3600 IN   CNAME   210.0/
          210.0/ 3600 IN PTR

      Above you can see it resolved to ""

      It's also possible to get all the zone information. The following command
      queries my local dns for the zone information.

          $ dig @ axfr    

      Reference ( )
        Also see TIP 223.

TIP 112:

       Using GNU Autotools - so you can produce the familiar "./configure"  "make"  and "make install"
                             commands. There is also a "make dist".

                The program and the rest of this code can be found at

         A "" is required:

            bin_PROGRAMS = sprog
            sprog_SOURCES =
            sprog_LDADD = @[email protected] @[email protected]

         In addition, a "" file is required. Note, AC_CHECK_LIB will
         check the "" file for the "sqlite3_open" file. Note that
         "sqlite3", is a shortcut for "libsqlite3" by convention. If this file
         is not found, AC_CHECK_FILE looks for "/usr/local/lib/libsqlite3.a". If
         this is found, then, "-lsqlite3" is added to the LIBS environment variable.
         Also, "-I/usr/local/include" and "-L/usr/local/lib" will be added on the
         command line. This is common when some one does not have the library in
         the path.  (See TIP 49)

            dnl Process this file with autoconf to produce a configure script.
            AM_INIT_AUTOMAKE(sqliteprog, 1.0)
            CXXFLAGS='-Wall -W -O2 -s -pipe'
             if test "$found" = "no"; then
               AC_CHECK_FILE(/usr/local/lib/libsqlite3.a, found=yes)
               if test "$found" = "yes"; then
                 LIBS="$LIBS -lsqlite3"
                 INCLUDES="$INCLUDES -I/usr/local/include"
                 echo "Are you SURE sqlite3 is installed?"

         To build the configure file, just run the following:

             $ aclocal
             $ autoconf
             $ touch NEWS README AUTHORS ChangeLog
             $ automake --add-missing

         Now if you want to make a tar.gz file "sqliteprog-1.0.tar.gz", then
         all you have to run is the following:

             $ make dist

         Note: did you ever want to save all the output from a ./configure? Well, it
               is automatically saved in the "config.log" file. In fact, this file may
               contain a lot more than what you saw on the screen.

               Also, you may need to rerun ./configure. But before you do, delete
               the "config.cache" file to get a clean build.

TIP 113:

       EMACS - common emacs commands.

         M is the ESC
         C or c is the Ctl

        Shell - when working in a shell. "M-x rename-uniquely" is good for split screen editing.

          M-x rename-uniquely   Use this for multiple shells (renames buffer so it's not the same shell)
          C-c C-z               Send job in background (when working in a shell)
          C-c C-o               commit-kill-output (gets rid of a lot of shell output)
          C-c C-r               reposition at beginning of output
          C-c C-e               reposition at end of output
          M-x send-invisible    Hide passwords - use this before typing a password

         Note: if the shell prompt does not show up correctly, then, you may want to creat a ".emacs_bash"
               file with the following contents:

                          PS1="emacs:\W \$ "

        Directories  (C-x d) give you a directory listing. You know all those annoying "~" and "#"
                     file that you get? You can easily delete these when in "dired" mode by hitting
                     "~", then  "d" to flag it for delete. Then, hit "x" to and confirm deletion.

                     These are other command that work on highlighted files in "dired" mode.

                          R   rename
                          v   view
                          Z   compress the file
                          +   create directory

        Other common commands:

          c-x l          list the line you are on, and how many lines in the document.
                         You will get something like: Page has 4881 lines (4440 + 442),
                         which means you are on the 4440 line.

          c-x rm bookmark make
          c-x rb bookmark bounce

          c-x rb notes
          c-x rb emacs

          c-x / <r> (save position in register <r>)
          c-x j <r> (jump to position in register <r>)
          c-x r SPC 1 (mark current point in register 1)
          c-x r j 1 (jump to marked point in register 1)
          c-x r t <string>  (insert string into register)

          c-x r s 1 (save marked region in register 1)
          c-x r i 1 (insert marked region)

          c-x c-o (delete all blank lines, except one)

          c-x z (repeat the last command ... stop with an a)
          c-x zz (repeat the last command twice)

          goto the next region
          then, C-x r r "name of register"

          to insert the register
          C-x r i "name of register"

          c-x (    start macro
          c-x )    end macro
          c-x e    execute macro

          c-x m   mail
          c-c c-s send

          C-x C-e
          (insert "\n\nExtra Line of text")

          ;; chirico functions in .emacs
          ;; This creates an html template
          (defun my-html ()
          (insert "<html>
          <META HTTP-EQUIV=\"Pragma\" CONTENT=\"no-cache\">
          <META HTTP-EQUIV=\"Expires\" CONTENT=\"-1\">
          <body bgcolor=\"#ffffff\">


     Backspace issues when using "emacs -nw"? They putting the following in your "~/.emacs" file

             (global-set-key "\C-d" 'backward-delete-char)
             (global-set-key "\C-h" 'backward-delete-char)
             (global-set-key (kbd "DEL") 'delete-char)

TIP 114:

        ncftpget - an intelligent ftp client ( Also
                   check your fedora or debian install. This package allows
                   you to easily download packages from ftp sites.

          This is an example of connect to an ftp site, with a subdirectory, and
          downloading all in one command.

           $ ncftpget

          Of if you want to get the fedora core 3 installs

           $ ncftpget*

TIP 115:

        expr - evaluate expressions. You can use this on the command line

           $ expr 6 + 4

         Note the spaces. Without spaces, you get the following:

           $ expr 6+4

         If you're using "*", you'll need a "\" before it

           $ expr 10 \* 10

         This also works for variables

           $ var1=34
           $ expr $var1 + 3


           $ var1=2
           $ var1=`expr $var1 \* 2`
           $ echo $var1

         see (TIP 25) you can get the cosine(.23)

           $ var1=`echo "c(.23)"|bc -l`
           $ echo $var1

         You can also do substrings:

           $ expr substr "BigBear" 4 4

         And length of strings

           $ mstr="12345"
           $ expr length $mstr

         Regular expressions

           $ expr "a3" : [a-z][1-9]

         Or you can get a bit fancy

           $ myexpr="[a-z][1-9]"
           $ echo $myexpr

           $ expr "a3" : $myexpr

         This may not be the best way to find out if it is Friday, but
         it seems to work. It's more of an exercise in xargs.

           $ date
           Fri Dec 31 16:44:47 EST 2004
           $ date|xargs -i expr {} : "[Fri]"

TIP 116:


           $ mypipe="|"
           $ eval ls $mypipe wc
           6       6     129

        Did you catch that? The above statement is the same as

           $ ls | wc

        Where "|" is put into the variable $mypipe

        (also see TIP 118)

TIP 117:

        lxr, glimpse, patchset - tools for reading the kernel source

          Note before going through all this trouble, you may find what
          you're looking for at the following site:


          This example puts some of the files in /home/src since my home
          partition is the largest. Plus, you do not want to over write
          the source in /usr/src/ If you want to put your files elsewhere
          just substitute /home/src for your desired directory.

         patchset -- download and setup

            $ export SRCDIR=/home/src
            $ cd $SRCDIR
            $ wget
            $ export PATH=$PATH:$SRCDIR/patchset-0.5/bin

          Now edit "/home/src/patchset-0.5/etc/patchset.conf" and set WWW_USER to
          whatever your website runs as

                  export WWW_USER=nobody

          Getting kernel source. The last step builds and asks a lot of questions. Enter
          yes to things that interest you, since this is what you will see in the source
          code. It is not going to build for booting. The "downlaod -p" is for downloading
          a patch.

            $ download 2.6.10
            $ createset 2.6.10
            $ make-kernel -b 2.6.10

        glimpse -- download and setup

            $ mkdir -p /home/src/glimpse
            $ cd /home/src/glimpse
            $ wget
            $ tar -xzf glimpse-latest.tar.gz
            $ cd glimpse-4.18.0
            $ ./configure; make
            $ make install

        lxr -- download and setup

            $ make -p /home/src/lxr
            $ cd /home/src/lxr
            $ wget
            $ cd lxr-0.3

          Edit "Makefile" and set PERLBIN to "/usr/bin/perl" or the where perl is
          on your system. Also set INSTALLPREFIX to "/var/www/lxr".  Then, as root
          do the following:

            $ make install

         Apache changes

          Next edit the apache httpd.conf. On my system it is
          "/usr/local/apache2/conf/httpd.conf", but if you did a fedora install
          I think this file is located at "/etc/httpd/conf/httpd.conf".

             Alias  /lxr/ "/var/www/lxr/"
             <Directory "/var/www/lxr/">
               Options ExecCGI Indexes Includes FollowSymLinks MultiViews
                AllowOverride all
                Order allow,deny
                Allow from all

              <Files ~ (search|source|ident|diff|find)>
                    SetHandler cgi-script

          lxr - continued "/var/www/lxr/http/lxr.conf" changes.  The following contains
                my lxr.conf with changes made to almost every variable. Make sure you use
                your website in place of

                 # Configuration file.

                 # Define typed variable "v", read valueset from file.
                 variable: v, Version, [/var/www/lxr/source/versions], [/var/www/lxr/source/defversion]

                 # Define typed variable "a".  First value is default.
                 variable: a, Architecture, (i386, alpha, m68k, mips, ppc, sparc, sparc64)

                 # Define the base url for the LXR files.

                 # These are the templates for the HTML heading, directory listing and
                 # footer, respectively.
                 htmlhead: /var/www/lxr/http/template-head
                 htmltail: /var/www/lxr/http/template-tail
                 htmldir:  /var/www/lxr/http/template-dir

                 # The source is here.
                 sourceroot: /var/www/lxr/source/$v/
                 srcrootname: Linux

                 # "#include <foo.h>" is mapped to this directory (in the LXR source
                 # tree)
                 incprefix: /include

                 # The database files go here.
                 dbdir: /var/www/lxr/source/$v/

                 # Glimpse can be found here.
                 glimpsebin: /usr/local/bin/glimpse

                 # The power of regexps.  This is pretty Linux-specific, but quite
                 # useful.  Tinker with it and see what it does.  (How's that for
                 # documentation?)
                 map: /include/asm[^\/]*/ /include/asm-$a/
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