### Commands by mkc (9) the last day the last week the last month all time sorted by date votes

• This command is somewhat similar to 'nice', but constrains I/O usage rather than CPU usage. In particular, the '-c3' flag tells the OS to only allow the process to do I/O when nothing else is pending. This dramatically increases the responsiveness of the rest of the system if the process is doing heavy I/O. There's also a '-p' flag, to set the priority of an already-running process.

6
ionice -c3 find /
· 2009-02-19 17:23:12
• The Linux /dev/full file simulates a "disk full" condition, and can be used to verify how a program handles this situation. In particular, several programming language implementations do not print error diagnostics (nor exit with error status) when I/O errors like this occur, unless the programmer has taken additional steps. That is, simple code in these languages does not fail safely. In addition to Perl, C, C++, Tcl, and Lua (for some functions) also appear not to fail safely. Show Sample Output

8
perl -e 'print 1, 2, 3' > /dev/full
· 2009-02-19 17:08:13
• The backslash avoids any 'rm' alias that might be present and runs the 'rm' command in $PATH instead. In a misguided attempt to be more "friendly", some Linux distributions (or sites/etc.) alias 'rm' to 'rm -i'. Unfortunately, this trains users to expect that files won't actually be deleted until they okay it. This expectation will fail with catastrophic results when they use other distributions, move to other sites, etc., and doesn't really even work 100% even with the alias. It's too late to fix 'rm', but '\rm' should work everywhere (under bash). 3 \rm somefile · 2009-02-19 16:55:54 • This is the setup I'm using for my largest project. It gives 357 lines per page (per side), which makes it fairly easy to carry around a significant amount of code on a few sheets of paper. Try it. (I stick to the 80 column convention in my coding. For wider code, you'll have to adjust this.) 1 enscript -E -B -3 -r -s 0 --borders -fCourier4.8 --mark-wrapped-lines=arrow · 2009-02-09 06:23:38 • The date command does offset calculations nicely, handles concepts like "a month" as you'd expect, and is good for offsets of at least 100M years in either direction. Show Sample Output 3 date --date="1 fortnight ago" · 2009-02-06 20:57:59 • strace can be invaluable in trying to figure out what the heck some misbehaving program is doing. There are number of useful flags to limit and control its output, and to attach to already running programs. (See also 'ltrace'.) Show Sample Output 5 strace -f -s 512 -v ls -l · 2009-02-06 02:45:33 • This is priceless for discovering otherwise invisible characters in files. Like, for example, that stray Control-M at the end of the initial hash bang line in your script, which causes it to generate a mysterious error even though it looks fine. ('od' is the last word, of course, but for many purposes it's much harder to read.) 0 cat -A · 2009-02-06 02:37:51 • This is a quick and dirty way to generate a (non-floating-point) CPU-bound task to benchmark. Adjust "20" to higher or lower values, as needed. As a benchmark this is probably a little less bogus than bogomips, and it will run anywhere 'bc' does. Show Sample Output 2 echo '2^2^20' | time bc > /dev/null · 2009-02-06 02:31:55 • This command repeatedly gets the specified process' stack using pstack (which is an insanely clever and tiny wrapper for gdb) and displays it fullscreen. Since it updates every second, you rapidly get an idea of where your program is stuck or spending time. The 'tac' is used to make the output grow down, which makes it less jumpy. If the output is too big for your screen, you can always leave the 'tac' off to see the inner calls. (Or, better yet--get a bigger screen.) Caveats: Won't work with stripped binaries and probably not well with threads, but you don't want to strip your binaries or use threads anyway. Show Sample Output 8 watch -n 1 'pstack 12345 | tac' · 2009-02-05 18:17:00 ### What's this? commandlinefu.com is the place to record those command-line gems that you return to again and again. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down. ### Check These Out find and delete empty dirs, start in current working dir Sum columns from CSV column$COL

find files ignoring .svn and its decendents
for when find . -print | grep -v .svn | xargs doesnt cut it.

Swap a file or dir with quick resotre
This lets you replace a file or directory and quickly revert if something goes wrong. For example, the current version of a website's files are in public_html. Put a new version of the site in public_html~ and execute the command. The names are swapped. If anything goes wrong, execute it again (up arrow or !!).

Use Perl like grep
If you've ever tried "grep -P" you know how terrible it is. Even the man page describes it as "highly experimental". This function will let you 'grep' pipes and files using Perl syntax for regular expressions. The first argument is the pattern, e.g. '/foo/'. The second argument is a filename (optional).

Find the package a command belongs to on debian-based distros
Advanced revision to the command 8776 . This revision follows symbolic links. The quotation-marks surrounding $(which$1) allows for graceful handling of errors ( ie. readlink does not complain incase 'which' command generates (null) output)

list block devices
Shows all block devices in a tree with descruptions of what they are.

Backup your hard drive with dd
This will create an exact duplicate image of your hard drive that you can then restore by simply reversing the "if" & "of" locations. $sudo dd if=/media/disk/backup/sda.backup of=/dev/sda Alternatively, you can use an SSH connection to do your backups:$dd if=/dev/sda | ssh user@ssh.server.com dd of=~/backup/sda.backup

Which processes are listening on a specific port (e.g. port 80)
swap out "80" for your port of interest. Can use port number or named ports e.g. "http"

Send apache log to syslog-ng
Send apache log to syslog-ng server without change configuration of syslog. Just add in httpd.conf or vhost conf.