Mike Chirico (mchirico@users.sourceforge.net) or (mchirico@gmail.com) Copyright (C) 2004 (GNU Free Documentation License) Last Updated: Sat May 14 19:55:58 EDT 2011 Currently 287 tips. The latest version of this document can be found at: http://chirico.googlecode.com/svn/trunk/Documentation/Articles/Linux/How_to_Linux_and_Open_Source.txt Or you can download the document: http://prdownloads.sourceforge.net/souptonuts/How_to_Linux_and_Open_Source.txt?download For tips on Gmail with Postix and Fetchmail http://souptonuts.sourceforge.net/postfix_tutorial.html For tips on using SQLite (over 25 pages) http://prdownloads.sourceforge.net/souptonuts/README_sqlite_tutorial.html?download For tips on MySQL reference: http://prdownloads.sourceforge.net/souptonuts/README_mysql.txt?download For a recommended reading list http://prdownloads.sourceforge.net/souptonuts/Recommended_Reading.html?download For tips on upgrading RedHat 9 or 8.0 to 2.6.x src kernel http://prdownloads.sourceforge.net/souptonuts/README_26.txt?download For tips on Comcast Email with Home Linux Box http://prdownloads.sourceforge.net/souptonuts/README_COMCAST_EMAIL.txt?download **Note, if you want email notification after every 50 new tips have been added, then, click on the following link: https://sourceforge.net/project/filemodule_monitor.php?filemodule_id=120838 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 =================================================== tock.usno.navy 0.0.0.0 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 ======================================================== +128.4.40.12 128.4.40.10 2 u 107 128 377 25.642 3.350 1.012 127.127.1.0 127.127.1.0 10 l 40 64 377 0.000 0.000 0.008 +128.91.2.13 128.4.40.12 3 u 34 128 377 21.138 6.118 0.398 *192.5.41.41 .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. server timeserver1.upenn.edu # ping -a timeserver1.upenn.edu shows the IP address 128.91.2.13 # which is used in the restrict below restrict 128.91.2.13 server tock.usno.navy.mil restrict 192.5.41.41 server 128.4.40.12 restrict 128.4.40.12 server 127.127.1.0 # local clock fudge 127.127.1.0 stratum 10 driftfile /etc/ntp/drift restrict default ignore restrict 127.0.0.0 mask 255.0.0.0 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 timeserver1.upenn.edu tock.usno.navy.mil 128.4.40.12 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 timeserver1.upenn.edu 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 SPECIAL NOTE: 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 documentation 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). October 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 31 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: http://sourceforge.net/direct-dl/mchirico/souptonuts/working_with_time.tar.gz Below is a bash script that will run the program for the next 100 days. #!/bin/bash # program: next100days Mike Chirico # download: # http://sourceforge.net/direct-dl/mchirico/souptonuts/working_with_time.tar.gz # # This will calculate the sunrise and sunset for # latitude 39.95 Note must convert to degrees # longitude 75.15 Note must convert to degrees lat=39.95 long=75.15 for (( i=0; i <= 100; i++)) do sunrise `date -d "+$i day" "+%Y %m %d"` $lat $long done 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 iso3166.tab 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 zone.tab 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 Reference: http://prdownloads.sourceforge.net/cpearls/date_calc.tar.gz?download 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 or $ find ../dir1/ | cpio -o -H tar > test2.tar Same command without the ">" $ find ../dir1/ | cpio -o --format=tar -F test.tar or $ find ../dir1/ | cpio -o -H tar -F test2.tar Using append $ find ../dir1/ | cpio -o --format=tar -F test.tar or $ find ../dir2/ | cpio -o --format=tar --append -F test.tar STEP 3 (List contents of the tar file) $ cpio -it < test.tar or $ 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 or $ 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 STEP 5 (ENCRYPTION) $ 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 well. $ 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) reference: http://cvs.sourceforge.net/viewcvs.py/cpearls/cpearls/src/posted_on_sf/acl/ehd.pdf?rev=1.1&view=log 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 DEVICE=eth0 BOOTPROTO=static BROADCAST=192.168.99.255 IPADDR=192.168.1.155 NETMASK=255.255.252.0 NETWORK=192.168.1.0 ONBOOT=yes STEP 2 (2nd IP address: ) $ cat /etc/sysconfig/network-scripts/ifcfg-eth0:1 DEVICE=eth0:1 BOOTPROTO=static BROADCAST=192.168.99.255 IPADDR=192.168.1.182 NETMASK=255.255.252.0 NETWORK=192.168.1.0 ONBOOT=yes 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 ... share:x:502:chirico,donkey,zoe ... ^------- 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 /usr/share/man:/usr/X11R6/man:/usr/local/share/man:/usr/local/pgsql/man:/usr/man:/usr/local/man 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 ^z $ 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 ports. $ 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 (squeezel.squeezel.com) 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 (http://perso.wanadoo.fr/sebastien.godard/download_en.html). You also may want to look at iozone (TIP 178). Also $ 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. Ref: http://www.teamquest.com/resources/gunther/ldavg1.shtml 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 /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 etc? $ 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/id_dsa.pub (Public key you can share) Next insert ".ssh/id_dsa.pub" 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 192.168.1.155 is the remote server and "donkey" is the account on that remote server. $ ssh donkey@192.168.1.155 "mkdir -p .ssh" $ ssh donkey@192.168.1.155 "chmod 700 .ssh" $ scp ./.ssh/id_dsa.pub donkey@192.168.1.155:.ssh/newkey.pub Now connect to that remote server "192.168.1.155" and add .ssh/newkey.pub to both "authorized_keys" and "authorized_keys2". When done, the permission on (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/id_dsa.pub|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 monthly # keep 4 weeks worth of backlogs # keep 12 months of backup rotate 12 # create new (empty) log files after rotating old ones create # uncomment this if you want your log files compressed compress # 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 { monthly 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 or $ 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 example 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 </Limit> 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 <Limit GET POST OPTIONS PROPFIND> Order allow,deny Allow from all </Limit> <LimitExcept GET POST OPTIONS PROPFIND> Order deny,allow Deny from all </LimitExcept> </Directory> 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 one/ one/test two/ 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: one/ one/test two/ At block 2: three/ three/samplehere four/ 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 Notes Take advantage of the label command. $ MYCOMMENTS="Big_important_tape" $ tar --label="$(date +%F)"+"${MYCOMMENTS}" Writing to tape on a remote 192.168.1.155 computer $ tar cvzf - ./tmp | ssh -l chirico 192.168.1.155 '(mt -f /dev/nst0 rewind; dd of=/dev/st0 )' Restoring the contents from tape on a remote computer $ ssh -l chirico 192.168.1.155 '(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 Reference: http://umn.dl.sourceforge.net/sourceforge/souptonuts/README_fedora.txt TIP 20: Getting Information about the Hard drive and list all PCI devices. $ hdparm /dev/hda /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 /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 /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 or $ cat /proc/partitions or $ 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" EDITOR=emacs 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: /etc/cron.hourly/ /etc/cron.daily/ /etc/cron.weekly/ /etc/cron.monthly/ 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 SHELL=/bin/bash PATH=/sbin:/bin:/usr/sbin:/usr/bin MAILTO=root HOME=/ # 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 "192.168.1.171" 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 donkey@192.168.1.171:/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 [http://www.rsnapshot.org/] 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 stuff stuffage stuffata stuffed stuffender stuffer stuffers stuffgownsman stuffier stuffiest stuffily stuffiness stuffinesses stuffiness's stuffing stuffings stuffing's stuffless stuffs stuffy It helps to have a large "linuxwords" dictionary. You can download a much bigger dictionary from the following: http://prdownloads.sourceforge.net/souptonuts/linuxwords.1.tar.gz?download 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> Example: $ 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 48 All functions with a "(" or ")" must be enclosed in quotes. For instance, to get the sin of .4 $ calc "s(.4)" .38941834230865049166 (See TIP 115 using the expr command) TIP 26: Kill a User and All Their Current Processes. #!/bin/bash # 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

",$0)}' or (ww = wide, wide output) $ ps auwwx| awk '!/'${USER}'/{printf("%s

",$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" 06172004 $ date -d '1 day ago' "+%m%d%Y" 06162004 $ 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

",msg }' or awk 'BEGIN { msg = "Don\x027t Panic!"; printf "%s

",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

")}' However, the line below works fine: awk 'BEGIN {printf("The D does not cause problems \047D

")}' 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 '

' 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 http://umn.dl.sourceforge.net/sourceforge/souptonuts/How_to_Linux_and_Open_Source.txt Or, better yet elinks. $ elinks http://somepage. You can get elinks at the following site: http://elinks.or.cz/ 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 or $ cat some_large_file | less or $ 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 m@temp.com is used here for login "anonymous". $ cat ~/.netrc machine upload.sourceforge.net login anonymous password m@temp.com default login anonymous password user@site It might be a good idea to change the rights on this file $ chmod 0400 ~/.netrc #!/bin/bash # # Sample ftp automated script to download # file to ${dwnld} # dwnld="/work/faq/unix-faq" cd ${dwnld} ftp << FTPSTRING prompt off open rtfm.mit.edu cd /pub/usenet-by-group/news.answers/unix-faq/faq mget contents mget diff mget part* bye FTPSTRING Sourceforge uses an anonymous login with an email address as a password. Below is the automated script I use for uploading binary files. #!/bin/bash # ftp sourceforge auto upload ftpup.sh # Usage: ./ftpup.sh <filename> # # machine upload.sourceforge.net user anonymous m@aol.com ftp -n -u << FTPSTRING open upload.sourceforge.net user anonymous m@aol.com binary cd incoming put ${1} bye FTPSTRING (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 ~ or $ cd To go back to the last directory $ cd - Instead of "cd" to a directory try "pushd" and look at the heading...you 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 "0". $ pwd /usr/local $ pushd +1 $ pwd /etc $ 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// /'

'} my stuff here 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 or $ echo -e "${p[*]}" one two three $ echo -e "${#p[@]}" 3 $ echo -e "${p[0]}" one $ echo -e "${p[1]}" two 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. $IFS=: $ for dir in $PATH > do > ls -ld $dir > done drwxr-xr-x 2 root root 4096 Jun 10 20:16 /usr/local/bin drwxr-xr-x 2 root root 4096 Jun 13 23:12 /bin drwxr-xr-x 3 root root 40960 Jun 12 08:00 /usr/bin drwxr-xr-x 2 root root 4096 Feb 14 03:12 /usr/X11R6/bin drwxrwxr-x 2 chirico chirico 4096 Jun 6 13:06 /home/chirico/bin Other ways of doing loops: for (( i=1; i <= 20; i++)) do echo -n "$i " done 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 4 3 2 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 Array[0]="zero" Array[1]="one" Array[2]="two" for i in `seq ${#Array[@]}` do echo $Array[$i-1] done 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 "/etc/fstab.bak". 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 file1 file2 $ 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 ' ' '

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

'|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 ' ' '

'|xargs -l3|tr ' ' '+'|bc 6 15 24 33 27 or $ tr ' ' '

' < 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 (http://www.shelldorado.com/) the above can be shortened as follows: $ tr ' ' '

' < 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 '

' (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 -- | /usr/local 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 Jacques.GARNIER-EXTERIEUR@EU.RHODIA.COM 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 81.169.158.205 $ tcpdump -i eth0 -nN -vvv -xX port not 22 and host 81.169.158.205 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? http://www.gnu.org/manual/manual.html Also worth a look the "Linux Documentation Project" http://en.tldp.org/ and Red Hat manuals http://www.redhat.com/docs/manuals/enterprise/ TIP 49: Setting or Changing the Library Path. The following contains the settings to be added or deleted /etc/ld.so.conf 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) { printf("%d

",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 library */ #include <libpersonal.h> #include <stdio.h> int main(int argc, char **argv) { test(45); } $ 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 src |-- prog |-- prog1 |-- prog1.c `-- test.c lib |-- libpersonal.a `-- test.o include `-- libpersonal.h This was a STATIC library. Often times you will want to use a SHARED or dynamic library. SHARED LIBRARY: You must recompile test.c with -fpic option. $ cd ../lib $ gcc -c -fpic ../src/test.c -o test.o Next create the libpersonal.so file. $ gcc -shared -o libpersonal.so 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 libpersonal.so => ../lib/libpersonal.so (0x40017000) libc.so.6 => /lib/tls/libc.so.6 (0x42000000) /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (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: libpersonal.so: 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 mikechirico@hotmail.com $ tail -f stuff | \ awk ' /now/ { system("mail -s \"This is working\" mikechirico@hotmail.com < msg") }' Or, you can run a program, say get headings on slashdot from the program "getslash.php" which runs on "192.168.1.155" with account "chirico". Assuming you have ssh keys setup, then, the following will send mail from the output: $ ssh chirico@192.168.1.155 "./bin/getslash.php"|mail -s "Slash cron Headlines" mchirico@comcast.net 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 chirico@192.168.1.155 "./bin/getslash.php"| \ awk '{ print $0 | "mail -s \x27 Slash Topics \x27 mchirico@comcast.net "}' Note the "\x27" is a quote. Maybe you only want articles dealing with "Linux": $ ssh chirico@192.168.1.155 "./bin/getslash.php"| \ awk '/Linux/{ print $0 | "mail -s \x27 Slash Topics \x27 mchirico@comcast.net "}' 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. http://sourceforge.net/projects/delcom/ (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 www.sourceforge.net:443 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 mail.comcast.net:995 -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 mail.comcast.net with proto POP3 and options no dns user 'zdonkey' with pass "somethin35" is 'donkey' here options ssl sslcertck sslcertpath '/home/donkey/.certs' smtphost comcast.net # currently not used mda '/usr/bin/procmail -d %T' REFERENCE: http://www.openssl.org/ http://www.catb.org/~esr/fetchmail/fetchmail-6.2.5.tar.gz http://www.madboa.com/geek/openssl/ 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 copy. 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 hours. $ find . -ctime -1 -printf "%a %f

" 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

" 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": http://sourceforge.net/project/showfiles.php?group_id=79320&package_id=80711 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 "/etc/security/time.conf" 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. Compile: gcc -o ctlgen ctlgen.c Run: ./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

",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. $@ 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 $? 0 And the following is false, which returns a 1. $ [[ -f /etc/passwdjabberwisnohere ]] $ echo $? 1 So true=0 and false=1. Sample program "mdo" to show the difference between "$@" and "$*" #!/bin/bash function myarg { echo "$# in myarg function" } echo -e "$# parameters on the cmd line

" echo -e "calling: myarg \"\$@\" and myarg \"\$*\"

" myarg "$@" myarg "$*" echo -e "

calling: myarg \$@ and myarg \$* without quotes

" myarg $@ myarg $* The result of running "./mdo one two". Note that when quoted, myarg "$*", returns 1 ... all parameters are smushed together as one word. [chirico@third-fl-71 theBook]$ ./mdo one two 2 parameters on the cmd line calling: myarg "$@" and myarg "$*" 2 in myarg function 1 in myarg function calling: myarg $@ and myarg $* without quotes 2 in myarg function 2 in myarg function Example program "mdo2" shows how the input separator can be changed. #!/bin/bash IFS=| echo -e "$*

" IFS=, echo -e "$*

" IFS=\; echo -e "$*

" IFS=$1 echo -e "$*

" [chirico@third-fl-71 theBook]$ ./mdo2 one two three four five one two three four five one,two,three,four,five one;two;three;four;five oneotwoothreeofourofive 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 ./Documentation/iostats.txt 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 "chirico@third-fl-71" and the Comcast email account is "mchirico@comcast.net". 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 "donkey@comcast.net"; yet, donkey would see the email from "mchirico@comcast.net" and not "chirico@third-fl-71" but chirico@third-fl-71 would get the replies. For a full description of how to solve this problem, including related "sendmail.mc", "site.config.m4", "genericstable", "genericsdomain", ".procmailrc", and ".forward" files, reference the following: http://prdownloads.sourceforge.net/souptonuts/README_COMCAST_EMAIL.txt?download 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)*

//" file Or, you may want to remove empty spaces and tabs at the end of a line $ perl -pi.backup -e "s/(\s)*

/

/" 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 substitution. TIP 70: Generating Random Numbers. $ od -vAn -N4 -tu4 < /dev/urandom 3905158199 TIP 71: Deleting a File by it's Inode Value. See (PROGRAMMING TIP 5) for creating the file, or $ cat > '













' type some text ^D 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 '{}' \; Reference: http://www.faqs.org/ftp/usenet/news.answers/unix-faq/faq/part2 TIP 72: Sending Attachments Using Mutt -- On the Command Line. $ mutt -s "See Attachment" -a file.doc user@domain.net < message.txt or just the message: $ echo | mutt -a sample.tar.gz user@domain.net Reference: http://www.shelldorado.com/articles/mailattachments.html 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 /usr/lib/libecpg.so.4 /usr/lib/libecpg.so.4.1 /usr/lib/libecpg_compat.so.1 /usr/lib/libecpg_compat.so.1.1 /usr/lib/libpgtypes.so.1 ... 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 /usr/share/doc/libpcap-0.8.3/CHANGES /usr/share/doc/libpcap-0.8.3/LICENSE /usr/share/doc/libpcap-0.8.3/README /usr/share/man/man3/pcap.3.gz 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 <sgrubb@redhat.com> 1.7.11-2 - Add crypto event definitions * Sat Jan 10 2009 Steve Grubb <sgrubb@redhat.com> 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 fi postuninstall scriptlet (using /bin/sh): if [ $1 -ge 1 ]; then /sbin/service auditd condrestart > /dev/null 2>&1 || : fi For dependencies listing, use the "R" option. $ rpm -qpR /iso0/Fedora/RPMS/libpcap-0.8.3-7.i386.rpm /sbin/ldconfig /sbin/ldconfig kernel >= 2.2.0 libc.so.6 libc.so.6(GLIBC_2.0) libc.so.6(GLIBC_2.1) libc.so.6(GLIBC_2.1.3) libc.so.6(GLIBC_2.3) openssl 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/libecpg.so.4.1 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: http://www-106.ibm.com/developerworks/library/l-rpm1/ To verify md5 sum so that you know it downloaded ok $ rpm -K *.rpm The following is a good reference: http://www.redhat.com/docs/books/max-rpm/max-rpm.pdf http://www.rpm.org/max-rpm/s1-rpm-install-additional-options.html TIP 75: Listing Output from a Bash Script. Add "set -x" #!/bin/bash set -x ls date 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 - http://prdownloads.sourceforge.net/souptonuts/How_to_Linux_and_Open_Source.txt?download|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:192.168.1.155 Bcast:192.168.99.255 Mask:255.255.252.0 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:192.168.1.182 Bcast:192.168.3.255 Mask:255.255.252.0 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:127.0.0.1 Mask:255.0.0.0 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.zip test.txt TIP 79: Need to Run Interactive Commands? Try "expect". http://expect.nist.gov/expect.tar.gz 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!". #!/usr/bin/expect set timeout 60 expect "hi

" send "hello there!

" Reference: http://www.oreilly.com/catalog/expect/chapter/ch03.html http://www.cotse.com/dlf/man/expect/bulletproof1.htm TIP 80: Using PHP as a Command Line Scripting Language. The following will grab the complete file from slashdot. #!/usr/bin/php -q <?php $fileName = "http://slashdot.org/slashdot.xml"; $rss = file($fileName) or die ("Cannot open file $fileName

"); 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: http://prdownloads.sourceforge.net/souptonuts/php_scripts.tar.gz?download 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: http://sourceforge.net/project/showfiles.php?group_id=13897 $ ./configure $ make $ make install Documentation can be found at the following link. The link on sourceforge is not correct, but, the one below works. http://www.gnu.org/software/mdk/manual/ TIP 83: Gnuplot [ http://sourceforge.net/projects/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) exit ^D 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' exit 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: http://souptonuts.sourceforge.net/povray/orbit.pov.html 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 ( http://www.imagemagick.org ). The following is "orbit.pov" #include "colors.inc" #include "finish.inc" #include "metals.inc" #include "textures.inc" #include "stones.inc" #include "skies.inc" 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 { S_Cloud3 } 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 { T_Silver_1E pigment {Yellow} } } #declare ball1= sphere { <3, 2, 0>, 0.5 texture { T_Silver_1E pigment {Blue} } } #declare ball2= sphere { <3, 1, 0>, 1 texture { T_Silver_1E 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: Output_File_Type=P Width=320 Height=240 Initial_Frame=1 Final_Frame=10 Antialias=true Subset_Start_Frame=1 Subset_End_Frame=10 Cyclic_Animation=on TIP 86: GPG -- GnuPG Reference: http://www.gnupg.org/documentation/faqs.html http://codesorcery.net/mutt/mutt-gnupg-howto http://www.gnupg.org/(en)/download/index.html (SCRIPT 4) on following link: http://prdownloads.sourceforge.net/souptonuts/README_common_script_commands.html?download 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 <mchirico@comcast.net> sub 1024g/E1A3C2B3 2004-07-15 Encrypt $ 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 or $ gpg -r Mike -e -a sample.txt or $ 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 /home/chirico/.gnupg/pubring.gpg v------------------ Use this with "0x" in front ------- pub 1024D/A11C1499 2004-07-15 Mike Chirico <mchirico@comcast.net> | sub 1024g/E1A3C2B3 2004-07-15 | | v---------------------------------------------------- $ gpg --send-keys 0xA11C1499 The above sends it to the keyserver defined in "/home/chirico/.gnupg/gpg.conf". Other key servers: wwwkeys.pgp.net search.keyserver.net pgp.ai.mit.edu 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 mchirico@comcast.net pub 1024D/A11C1499 2004-07-15 Key fingerprint = 9D7F C80D BB7B 4BAB CCA4 1BE9 9056 5BEC A11C 1499 uid Mike Chirico (http://souptonuts.sourceforge.net/chirico/index.php) <mchirico@comcast.net> sub 1024g/E1A3C2B3 2004-07-15 Receving keys: The following will retrieve my mchirico@comcast.net 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: http://prdownloads.sourceforge.net/souptonuts/README_common_script_commands.html?download 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: http://www.engelschall.com/u/sb/download/pkg/Date-Calc-5.3.tar.gz $ wget http://www.engelschall.com/u/sb/download/pkg/Date-Calc-5.3.tar.gz $ 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: http://prdownloads.sourceforge.net/cpearls/date_calc.tar.gz?download 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.+]+@[-a-z_0-9.]+" color body red default "(^| )\\*[-a-z0-9*]+\\*[,.?]?[

]" color body green default "(^| )_[-a-z0-9_]+_[,.?]?[

]" color body red default "(^| )\\*[-a-z0-9*]+\\*[,.?]?[

]" color body green default "(^| )_[-a-z0-9_]+_[,.?]?[

]" 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" PROCESS STATE CODES 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 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND 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/xinetd.pid ... It is also possible to list the process by command line. For example, the following command will only list the emacs processes. $ 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 # #VARIABLES: # %eax holds the system call number # (this is always the case) # # %ebx holds the return status # .section .data .section .text .globl _start _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 $? 0 That is about all it does; but, get the book for more details. The book is free. http://savannah.nongnu.org/download/pgubook/ 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 http://www.namesys.com/ 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 cpan> 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. Configuration. Edit the following "/etc/mail/spamassassin/local.cf" Here is a look at my file $ cat /etc/mail/spamassassin/local.cf # 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 PATH=/bin:/usr/bin:/usr/local/bin MAILDIR=/var/spool/mail DEFAULT=/var/spool/mail/chirico LOGFILE=/home/chirico/MailBAG MYHOME=/home/chirico # Must have folder MailTRASH TRASH=/home/chirico/MailTRASH # Will get everything from this mail :0 * ^From:.*sporkey@comcast.net $DEFAULT # Spamassassin :0fw * <300000 |/usr/local/bin/spamassassin Reference: http://pm-doc.sourceforge.net/ TIP 93: Make Graphs: using dot and neato. $ dot -Tpng dotfile -o myout.png To see the output reference the following: http://souptonuts.sourceforge.net/code/myout.png 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: http://www.linuxjournal.com/article.php?sid=7275 To download this software http://www.graphviz.org/ 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/libsqlite.so) sqlite3LIB := $(shell ls /usr/local/lib/libsqlite3.so) # all assumes sqlite and sqlite3 are installed # test: ifeq ("$(sqlite3LIB)","/usr/local/lib/libsqlite3.so") @echo -e "True -- we found the file" else @e