signal - list of available signals


Linux supports the signals listed below. Several signal numbers are architecture dependent. First the signals described in POSIX.1.

       Signal     Value     Action   Comment
       SIGHUP        1        A      Hangup detected on controlling terminal or
                                     death of controlling process
       SIGINT        2        A      Interrupt from keyboard
       SIGQUIT       3        C      Quit from keyboard
       SIGILL        4        C      Illegal Instruction
       SIGABRT       6        C      Abort signal from abort(3)
       SIGFPE        8        C      Floating point exception
       SIGKILL       9       AEF     Kill signal
       SIGSEGV      11        C      Invalid memory reference
       SIGPIPE      13        A      Broken pipe: write to pipe with no readers
       SIGALRM      14        A      Timer signal from alarm(2)
       SIGTERM      15        A      Termination signal
       SIGUSR1   30,10,16     A      User-defined signal 1
       SIGUSR2   31,12,17     A      User-defined signal 2
       SIGCHLD   20,17,18     B      Child stopped or terminated
       SIGCONT   19,18,25            Continue if stopped
       SIGSTOP   17,19,23    DEF     Stop process
       SIGTSTP   18,20,24     D      Stop typed at tty
       SIGTTIN   21,21,26     D      tty input for background process
       SIGTTOU   22,22,27     D      tty output for background process

Next the signals not in POSIX.1 but described in SUSv2.

       Signal       Value     Action   Comment
       SIGBUS      10,7,10      C      Bus error (bad memory access)
       SIGPOLL                  A      Pollable event (Sys V). Synonym of SIGIO
       SIGPROF     27,27,29     A      Profiling timer expired
       SIGSYS      12,-,12      C      Bad argument to routine (SVID)
       SIGTRAP        5         C      Trace/breakpoint trap
       SIGURG      16,23,21     B      Urgent condition on socket (4.2 BSD)
       SIGVTALRM   26,26,28     A      Virtual alarm clock (4.2 BSD)
       SIGXCPU     24,24,30     C      CPU time limit exceeded (4.2 BSD)
       SIGXFSZ     25,25,31     C      File size limit exceeded (4.2 BSD)

(For the cases SIGSYS, SIGXCPU, SIGXFSZ, and on some architectures also SIGBUS, the Linux default action up to now (2.3.27) is A (terminate), while SUSv2 prescribes C (terminate and dump core).)

Next various other signals.

       Signal       Value     Action   Comment
       SIGIOT         6         C      IOT trap. A synonym for SIGABRT
       SIGEMT       7,-,7
       SIGSTKFLT    -,16,-      A      Stack fault on coprocessor
       SIGIO       23,29,22     A      I/O now possible (4.2 BSD)

       SIGCLD       -,-,18             A synonym for SIGCHLD
       SIGPWR      29,30,19     A      Power failure (System V)
       SIGINFO      29,-,-             A synonym for SIGPWR
       SIGLOST      -,-,-       A      File lock lost
       SIGWINCH    28,28,20     B      Window resize signal (4.3 BSD, Sun)
       SIGUNUSED    -,31,-      A      Unused signal (will be SIGSYS)

(Here - denotes that a signal is absent; there where three values are given, the first one is usually valid for alpha and sparc, the middle one for i386 and ppc and sh, the last one for mips. Signal 29 is SIGINFO / SIGPWR on an alpha but SIGLOST on a sparc.)

The letters in the "Action" column have the following meanings:

Default action is to terminate the process.
Default action is to ignore the signal.
Default action is to terminate the process and dump core.
Default action is to stop the process.
Signal cannot be caught.
Signal cannot be ignored.




SIGIO and SIGLOST have the same value. The latter is commented out in the kernel source, but the build process of some software still thinks that signal 29 is SIGLOST.


kill(1), kill(2), setitimer(2)

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