Originální popis anglicky:
signal - list of available signals
Linux supports both POSIX reliable signals (hereinafter "standard
signals") and POSIX real-time 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:
- Term
- Default action is to terminate the process.
- Ign
- Default action is to ignore the signal.
- Core
- Default action is to terminate the process and dump
core.
- Stop
- Default action is to stop the process.
First the signals described in the original POSIX.1 standard.
| Signal |
Value |
Action |
Comment |
|
|
|
|
| SIGHUP |
1 |
Term |
Hangup detected on controlling terminal |
|
|
|
or death of controlling process |
| SIGINT |
2 |
Term |
Interrupt from keyboard |
| SIGQUIT |
3 |
Core |
Quit from keyboard |
| SIGILL |
4 |
Core |
Illegal Instruction |
| SIGABRT |
6 |
Core |
Abort signal from abort(3) |
| SIGFPE |
8 |
Core |
Floating point exception |
| SIGKILL |
9 |
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 alarm(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 |
The signals
SIGKILL and
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.
| 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) |
Up to and including Linux 2.2, the default behaviour for
SIGSYS,
SIGXCPU,
SIGXFSZ, and (on architectures other than SPARC and
MIPS)
SIGBUS was to terminate the process (without a core dump). (On
some other Unices the default action for
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.
| 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) |
(Signal 29 is
SIGINFO /
SIGPWR on an alpha but
SIGLOST on a
sparc.)
SIGEMT is not specified in POSIX 1003.1-2001, but neverthless appears on
most other Unices, where its default action is typically to terminate the
process with a core dump.
SIGPWR (which is not specified in POSIX 1003.1-2001) is typically ignored
by default on those other Unices where it appears.
SIGIO (which is not specified in POSIX 1003.1-2001) is ignored by default
on several other Unices.
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 (
SIGRTMIN) to 63 (
SIGRTMAX).
(Programs should always refer to real-time signals using notation
SIGRTMIN+n, since the range of real-time signal numbers varies across
Unices.)
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.)
The default action for an unhandled real-time signal is to terminate the
receiving process.
Real-time signals are distinguished by the following:
- 1.
- 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.
- 2.
- If the signal is sent using 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 SA_SIGACTION flag to sigaction(2) then it can
obtain this data via the si_value field of the siginfo_t
structure passed as the second argument to the handler. Furthermore, the
si_pid and si_uid fields of this structure can be used to
obtain the PID and real user ID of the process sending the signal.
- 3.
- 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.)
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.
According to POSIX, an implementation should permit at least _POSIX_SIGQUEUE_MAX
(32) real-time signals to be queued to a process. However, rather than placing
a per-process limit, 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
/proc/sys/kernel/rtsig-max file. A related
file,
/proc/sys/kernel/rtsig-nr, can be used to find out how many
real-time signals are currently queued.
POSIX.1
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),
sigaction(2),
signal(2),
sigprocmask(2),
sigqueue(2)
