(coreutils.info)Signal specifications

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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’.