2.5 Signal specifications

A signal may be a signal name like ‘HUP’, or a signal number like ‘1’, or an exit status of a process terminated by the signal. A signal name can be given in canonical form or prefixed by ‘SIG’. The case of the letters is ignored. The following signal names and numbers are supported on all POSIX compliant systems:

HUP
1. Hangup.
INT
2. Terminal interrupt.
QUIT
3. Terminal quit.
ABRT
6. Process abort.
KILL
9. Kill (cannot be caught or ignored).
ALRM
14. Alarm Clock.
TERM
15. Termination.

Other supported signal names have system-dependent corresponding numbers. All systems conforming to POSIX 1003.1-2001 also support the following signals:

BUS
Access to an undefined portion of a memory object.
CHLD
Child process terminated, stopped, or continued.
CONT
Continue executing, if stopped.
FPE
Erroneous arithmetic operation.
ILL
Illegal Instruction.
PIPE
Write on a pipe with no one to read it.
SEGV
Invalid memory reference.
STOP
Stop executing (cannot be caught or ignored).
TSTP
Terminal stop.
TTIN
Background process attempting read.
TTOU
Background process attempting write.
URG
High bandwidth data is available at a socket.
USR1
User-defined signal 1.
USR2
User-defined signal 2.

POSIX 1003.1-2001 systems that support the XSI extension also support the following signals:

POLL
Pollable event.
PROF
Profiling timer expired.
SYS
Bad system call.
TRAP
Trace/breakpoint trap.
VTALRM
Virtual timer expired.
XCPU
CPU time limit exceeded.
XFSZ
File size limit exceeded.

POSIX 1003.1-2001 systems that support the XRT extension also support at least eight real-time signals called ‘RTMIN’, ‘RTMIN+1’, …, ‘RTMAX-1’, ‘RTMAX’.