blag/post/a-lesser-known-feature-of-kill-1-.mdwn

   1 [[!meta title="A Lesser-Known Feature of kill(1)"]]
   2 [[!meta author="rohieb"]]
   3 [[!meta license="CC-BY-SA 3.0"]]
   4
   5 ## Problem ##
   6 I was debugging a program, which suddenly died with
   7
   8     QFATAL : TestEdge::testSaveRemove() Received signal 11
   9
  10 For better understanding of the problem, it would be nice to know what
  11 the meaning of “signal 11” is.
  12
  13
  14 ## Solution ##
  15 I was not so fluent in signal numbers (maybe I should take [a
  16 course][memrise]). Of course, I _could_ dig in the [`signal(7)` man
  17 page][mansignal], or in the respective C header (`signal.h`). However,
  18 while digging in the manpages, I noticed that `kill(1)` does not only
  19 kill processes, but also does exactly what I want.[^1] Citing from the
  20 [man page][mankill]:
  21
  22     -l, --list [signal]
  23       List  signal  names.   This  option has optional argument, which
  24       will convert signal number to signal name, or other way round.
  25
  26 [^1]: At least the version in Debian, which is from
  27     [procps](https://gitorious.org/procps)
  28
  29 So I could just say:
  30
  31     $ kill -l 11
  32     SEGV
  33
  34 Ah, segmentation fault. Nice to know :-)
  35
  36 In addition, the man page also mentions a useful parameter `-L`, which
  37 prints a nice table of signal numbers and mnemonics:
  38
  39     $ /bin/kill -L
  40      1 HUP      2 INT      3 QUIT     4 ILL      5 TRAP     6 ABRT  7 BUS
  41      8 FPE      9 KILL    10 USR1    11 SEGV    12 USR2    13 PIPE 14 ALRM
  42     15 TERM    16 STKFLT  17 CHLD    18 CONT    19 STOP    20 TSTP 21 TTIN
  43     22 TTOU    23 URG     24 XCPU    25 XFSZ    26 VTALRM  27 PROF 28 WINCH
  44     29 POLL    30 PWR     31 SYS
  45
  46 (Also, the man page also warns about `kill` probably being a shell
  47 built-in. At least the Bash and zsh built-ins also know `-l`, but not
  48 `-L`, so you have to call `/bin/kill` explicitly.)
  49
  50 [memrise]: http://www.memrise.com/course/158486/unix-signals/
  51 [mansignal]: http://manpages.debian.net/cgi-bin/man.cgi?query=signal&apropos=0&sektion=7&manpath=Debian+7.0+wheezy&format=html&locale=en
  52 [mankill]: http://manpages.debian.net/cgi-bin/man.cgi?query=kill&apropos=0&sektion=0&manpath=Debian+7.0+wheezy&format=html&locale=en
  53
  54 [[!tag UNIX Linux Debian UNIX_signal_numbers signal.h SIGSEGV kill]]