### 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

9
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

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### Check These Out

Create a bunch of dummy text files
Avoiding a for loop brought this time down to less than 3 seconds on my old machine. And just to be clear, 33554432 = 8192 * 4086.

Sets shell timeout
Useful in root's .profile - will auto-logout after TMOUT seconds of inactivity. Close after seconds inactive. export TMOUT=seconds (unefunge)

Find usb device in realtime
Using this command you can track a moment when usb device was attached.

Output a list of svn repository entities to xml file
I use this to pull the last commit date for everything in my repo, so I can tell the client which files haven't been touched or updated since the repo was created. Another way to do it is to use svn log, but that does not pull the "kind" attribute. It does, however, give you the commit message. Both are very useful.

Execute a command at a given time
This is an alternative to cron which allows a one-off task to be scheduled for a certain time.

Calculate days on which Friday the 13th occurs
I removed the dependency of the English language

urldecoding with one pure BASH builtin
You can use ordinary printf to convert "%23%21%2fbin%2fbash" into "#!/bin/bash" with no external utilities, by using a little known printf feature -- the "%b" specifier converts shell escapes. Replace % with \x and printf will understand the urlencoded string. BASH's printf has an extension to set a variable directly, too. So you get to convert urlencoded strings from garble to plaintext in one step with no externals and no backticks.

Get a list of ssh servers on the local subnet
Scan the local network for servers who have the ssh port open.

Lists installed kernels
no need for rpm, no need for piping to another command. also no real fu but lacking in unnecessary complexity and distro specific commands.

List all installed Debian packages
Should work on all systems that use dpkg and APT package management.