SIGNAL

Section: Linux Programmer's Manual (7 )
Updated: 1996-04-14
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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

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

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

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.