NAME

signal - list of available signals

DESCRIPTION

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:

A

Default action is to terminate the process.

B

Default action is to ignore the signal.

C

Default action is to terminate the process and dump core.

D

Default action is to stop the process.

E

Signal cannot be caught.

F

Signal cannot be ignored.

CONFORMING TO

POSIX.1

BUGS

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.

SEE ALSO

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