Commands by mkc (9)

  • 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 /
    mkc · 2009-02-19 17:23:12 11
  • 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
    mkc · 2009-02-19 17:08:13 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
    mkc · 2009-02-19 16:55:54 12
  • 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
    mkc · 2009-02-09 06:23:38 15
  • 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"
    mkc · 2009-02-06 20:57:59 12
  • 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
    mkc · 2009-02-06 02:45:33 22
  • 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
    mkc · 2009-02-06 02:37:51 22
  • 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
    mkc · 2009-02-06 02:31:55 41
  • 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'
    mkc · 2009-02-05 18:17:00 30

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HDD Performance Write Test
Test your XFS filesystem and Raptor hard drives for write performance.

Merge files, joining each line in one line

archive all files containing local changes (svn)
This works more reliable for me ("cut -c 8-" had one more space, so it did not work)

Set all CPU cores' CPU frequency scaling governor to maximum performance

save your current environment as a bunch of defaults

Count lines of source code excluding blank lines and comments
Much more accurate than other methods mentioned here straight out of the box.

Google text-to-speech in mp3 format

Archive all SVN repositories in platform indepenent form
Use of hotcopy for safety/stability of the backups.

Write comments to your history.
A null operation with the name 'comment', allowing comments to be written to HISTFILE. Prepending '#' to a command will *not* write the command to the history file, although it will be available for the current session, thus '#' is not useful for keeping track of comments past the current session.

Dump dvd from a different machine onto this one.
You can use this to directly dump from machine A (with dvd drive) to machine B (without dvd drive) . I used this to copy dvd using my friend's machine to my netbook. Above command is to be issued on machine B. Advantages : 1) No wasting time dumping first to machine A and then copying to Machine B. 2) You dont need to use space on Machine A. In fact, this will work even when Machine A doesnt have enough hdd space to dump the DVD. Use -C ssh option on slow networks (enables compression). you can replace "dd if=/dev/dvd" with any ripping command as long as it spews the iso to stdout.


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