'\" t .\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de) .\" Copyright (c) 2002 by Michael Kerrisk .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" Modified Sat Jul 24 17:34:08 1993 by Rik Faith (faith@cs.unc.edu) .\" Modified Sun Jan 7 01:41:27 1996 by Andries Brouwer (aeb@cwi.nl) .\" Modified Sun Apr 14 12:02:29 1996 by Andries Brouwer (aeb@cwi.nl) .\" Modified Sat Nov 13 16:28:23 1999 by Andries Brouwer (aeb@cwi.nl) .\" Modified 10 Apr 2002, by Michael Kerrisk .\" Modified 7 Jun 2002, by Michael Kerrisk .\" Added information on real-time signals .\" Modified 13 Jun 2002, by Michael Kerrisk .\" Noted that SIGSTKFLT is in fact unused .\" 2004-12-03, Modified mtk, added notes on RLIMIT_SIGPENDING .\" .TH SIGNAL 7 2002-06-13 "Linux 2.4.18" "Linux Programmer's Manual" .SH NAME signal \- list of available signals .SH DESCRIPTION Linux supports both POSIX reliable signals (hereinafter "standard signals") and POSIX real-time signals. .SS "Standard Signals" Linux supports the standard signals listed below. Several signal numbers are architecture dependent, as indicated in the "Value" column. (Where three values are given, the first one is usually valid for alpha and sparc, the middle one for i386, ppc and sh, and the last one for mips. A \- denotes that a signal is absent on the corresponding architecture.) The entries in the "Action" column of the table specify the default action for the signal, as follows: .IP Term Default action is to terminate the process. .IP Ign Default action is to ignore the signal. .IP Core Default action is to terminate the process and dump core. .IP Stop Default action is to stop the process. .PP First the signals described in the original POSIX.1 standard. .sp .PP .TS l c c l ____ lB c c l. Signal Value Action Comment SIGHUP \01 Term Hangup detected on controlling terminal or death of controlling process SIGINT \02 Term Interrupt from keyboard SIGQUIT \03 Core Quit from keyboard SIGILL \04 Core Illegal Instruction SIGABRT \06 Core Abort signal from \fIabort\fP(3) SIGFPE \08 Core Floating point exception SIGKILL \09 Term Kill signal SIGSEGV 11 Core Invalid memory reference SIGPIPE 13 Term Broken pipe: write to pipe with no readers SIGALRM 14 Term Timer signal from \fIalarm\fP(2) SIGTERM 15 Term Termination signal SIGUSR1 30,10,16 Term User\-defined signal 1 SIGUSR2 31,12,17 Term User\-defined signal 2 SIGCHLD 20,17,18 Ign Child stopped or terminated SIGCONT 19,18,25 Continue if stopped SIGSTOP 17,19,23 Stop Stop process SIGTSTP 18,20,24 Stop Stop typed at tty SIGTTIN 21,21,26 Stop tty input for background process SIGTTOU 22,22,27 Stop tty output for background process .TE The signals .B SIGKILL and .B SIGSTOP cannot be caught, blocked, or ignored. Next the signals not in the POSIX.1 standard but described in SUSv2 and SUSv3 / POSIX 1003.1-2001. .sp .PP .TS l c c l ____ lB c c l. Signal Value Action Comment SIGBUS 10,7,10 Core Bus error (bad memory access) SIGPOLL Term Pollable event (Sys V). Synonym of SIGIO SIGPROF 27,27,29 Term Profiling timer expired SIGSYS 12,\-,12 Core Bad argument to routine (SVID) SIGTRAP 5 Core Trace/breakpoint trap SIGURG 16,23,21 Ign Urgent condition on socket (4.2 BSD) SIGVTALRM 26,26,28 Term Virtual alarm clock (4.2 BSD) SIGXCPU 24,24,30 Core CPU time limit exceeded (4.2 BSD) SIGXFSZ 25,25,31 Core File size limit exceeded (4.2 BSD) .TE Up to and including Linux 2.2, the default behaviour for .BR SIGSYS ", " SIGXCPU ", " SIGXFSZ ", " and (on architectures other than SPARC and MIPS) .B SIGBUS was to terminate the process (without a core dump). (On some other Unices the default action for .BR SIGXCPU " and " SIGXFSZ is to terminate the process without a core dump.) Linux 2.4 conforms to the POSIX 1003.1-2001 requirements for these signals, terminating the process with a core dump. Next various other signals. .sp .PP .TS l c c l ____ lB c c l. Signal Value Action Comment SIGIOT 6 Core IOT trap. A synonym for SIGABRT SIGEMT 7,\-,7 Term SIGSTKFLT \-,16,\- Term Stack fault on coprocessor (unused) SIGIO 23,29,22 Term I/O now possible (4.2 BSD) SIGCLD \-,\-,18 Ign A synonym for SIGCHLD SIGPWR 29,30,19 Term Power failure (System V) SIGINFO 29,\-,\- A synonym for SIGPWR SIGLOST \-,\-,\- Term File lock lost SIGWINCH 28,28,20 Ign Window resize signal (4.3 BSD, Sun) SIGUNUSED \-,31,\- Term Unused signal (will be SIGSYS) .TE (Signal 29 is .B SIGINFO / .B SIGPWR on an alpha but .B SIGLOST on a sparc.) .B SIGEMT is not specified in POSIX 1003.1-2001, but nevertheless appears on most other Unices, where its default action is typically to terminate the process with a core dump. .B SIGPWR (which is not specified in POSIX 1003.1-2001) is typically ignored by default on those other Unices where it appears. .B SIGIO (which is not specified in POSIX 1003.1-2001) is ignored by default on several other Unices. .SS "Real-time Signals" Linux supports real-time signals as originally defined in the POSIX.4 real-time extensions (and now included in POSIX 1003.1-2001). Linux supports 32 real-time signals, numbered from 32 .RB ( SIGRTMIN ) to 63 .RB ( SIGRTMAX ). (Programs should always refer to real-time signals using notation .BR SIGRTMIN +n, since the range of real-time signal numbers varies across Unices.) .PP Unlike standard signals, real-time signals have no predefined meanings: the entire set of real-time signals can be used for application-defined purposes. (Note, however, that the LinuxThreads implementation uses the first three real-time signals.) .PP The default action for an unhandled real-time signal is to terminate the receiving process. .PP Real-time signals are distinguished by the following: .IP 1. 4 Multiple instances of real-time signals can be queued. By contrast, if multiple instances of a standard signal are delivered while that signal is currently blocked, then only one instance is queued. .IP 2. 4 If the signal is sent using .BR sigqueue (2), an accompanying value (either an integer or a pointer) can be sent with the signal. If the receiving process establishes a handler for this signal using the .B SA_SIGINFO flag to .BR sigaction (2) then it can obtain this data via the .I si_value field of the .I siginfo_t structure passed as the second argument to the handler. Furthermore, the .I si_pid and .I si_uid fields of this structure can be used to obtain the PID and real user ID of the process sending the signal. .IP 3. 4 Real-time signals are delivered in a guaranteed order. Multiple real-time signals of the same type are delivered in the order they were sent. If different real-time signals are sent to a process, they are delivered starting with the lowest-numbered signal. (I.e., low-numbered signals have highest priority.) .PP If both standard and real-time signals are pending for a process, POSIX leaves it unspecified which is delivered first. Linux, like many other implementations, gives priority to standard signals in this case. .PP According to POSIX, an implementation should permit at least _POSIX_SIGQUEUE_MAX (32) real-time signals to be queued to a process. However, Linux does things differently. In kernels up to and including 2.6.7, Linux imposes a system-wide limit on the number of queued real-time signals for all processes. This limit can be viewed and (with privilege) changed via the .I /proc/sys/kernel/rtsig-max file. A related file, .IR /proc/sys/kernel/rtsig-nr , can be used to find out how many real-time signals are currently queued. In Linux 2.6.8, these .I /proc interfaces were replaced by .B RLIMIT_SIGPENDING resource limit, which specifies a per-user limit for queued signals; see .BR setrlimit (2) for further details. .SH "CONFORMING TO" POSIX.1 .SH BUGS .B SIGIO and .B 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 .BR SIGLOST . .SH "SEE ALSO" .BR kill (1), .BR kill (2), .BR setitimer (2), .BR setrlimit (2), .BR sigaction (2), .BR signal (2), .BR sigprocmask (2), .BR sigqueue (2), .BR proc (5)