SIGNAL(3C) COMMAND REFERENCE SIGNAL(3C)
NAME
signal - simplified software signal facilities
SYNOPSIS
#include <signal.h>
(*signal(sig, func))()
int (*func)();
DESCRIPTION
Signal is a simplified interface to the more general
sigvec(2) facility.
A signal is generated by some abnormal event, initiated by a
user at a terminal ( quit, interrupt, stop), by a program
error (bus error, and so forth), by request of another
program (kill), or when a process is stopped because it
wishes to access its control terminal while in the
background (see tty(4)). Signals are optionally generated
when a process resumes after being stopped, when the status
of child processes changes, or when input is ready at the
control terminal. Most signals cause termination of the
receiving process if no action is taken; some signals
instead cause the process receiving them to be stopped, or
are simply discarded if the process has not requested
otherwise. Except for the SIGKILL and SIGSTOP signals, the
signal call allows signals either to be ignored or to cause
an interrupt to a specified location. The following is a
list of all signals with names as in the include file
<signal.h>. The sig parameters are listed in the first
column.
SIGHUP 1 hangup
SIGINT 2 interrupt
SIGQUIT 3* quit
SIGILL 4* illegal instruction (not reset when caught)
SIGTRAP 5* trace trap (not reset when caught)
SIGIOT 6* IOT instruction
SIGEMT 7* EMT instruction
SIGFPE 8* floating point exception
SIGKILL 9 kill (cannot be caught or ignored)
SIGBUS 10* bus error
SIGSEGV 11* segmentation violation
SIGSYS 12* bad argument to system call
SIGPIPE 13 write on a pipe with no one to read it
SIGALRM 14 alarm clock
SIGTERM 15 software termination signal from kill
SIGURG 16• urgent condition present on socket,
exception condition present on device
SIGSTOP 17† stop (cannot be caught or ignored)
SIGTSTP 18† stop signal generated from keyboard
SIGCONT 19• continue after stop (cannot be blocked)
Printed 10/17/86 1
SIGNAL(3C) COMMAND REFERENCE SIGNAL(3C)
SIGCHLD 20• to parent on child stop or exit
SIGTTIN 21† background read attempted from control terminal
SIGTTOU 22† background write attempted to control terminal
SIGIO 23• I/O is possible on a descriptor (see fcntl(2))
SIGXCPU 24 CPU time limit exceeded (see setrlimit(2))
SIGXFSZ 25 file size limit exceeded (see setrlimit(2))
SIGVTALRM 26 virtual time alarm (see setitimer(2))
SIGPROF 27 profiling timer alarm (see setitimer(2))
The following signals are not yet implemented, but are
planned for a later release of the system:
SIGUSR1 28 user-defined signal 1
SIGUSR2 29 user-defined signal 2
SIGCLD 30 death of a child
SIGPWR 31 power fail
The starred signals in the list above cause a core image if
not caught or ignored.
If func is SIG_DFL, the default action for signal sig is
reinstated; this default is termination (with a core image
for starred signals) except for signals marked with @ or
'
|+'. Signals marked with • are discarded if the action is
SIG_DFL; signals marked with † cause the process to stop.
If func is SIG_IGN, the signal is subsequently ignored and
pending instances of the signal are discarded. Otherwise,
when the signal occurs further occurences of the signal are
automatically blocked and func is called.
A return from the function unblocks the handled signal and
continues the process at the point it was interrupted.
Note: Unlike previous signal facilities, the handler
func remains installed after a signal has been
delivered.
If a caught signal occurs during certain system calls,
causing the call to terminate prematurely, the call is
automatically restarted. In particular, this can occur
during a read(2) or write(2) on a slow device (such as a
terminal; but not a file) and during a wait(2).
The value of signal is the previous (or initial) value of
func for the particular signal.
After a fork(2) or vfork(2) the child inherits all signals.
Execve(2) resets all caught signals to the default action;
ignored signals remain ignored.
DIAGNOSTICS
Signal will fail and no action will take place if one of the
Printed 10/17/86 2
SIGNAL(3C) COMMAND REFERENCE SIGNAL(3C)
following occurs:
[EINVAL]
Sig is not a valid signal number.
[EINVAL]
An attempt is made to ignore or supply a handler for
SIGKILL or SIGSTOP.
[EINVAL]
An attempt is made to ignore SIGCONT (by default SIGCONT
is ignored).
RETURN VALUE
The previous action is returned on a successful call.
Otherwise, -1 is returned and errno is set to indicate the
error.
SEE ALSO
kill(1), kill(2), ptrace(2), sigblock(2), sigpause(2),
sigsetmask(2), sigstack(2), sigvec(2), setjmp(3c), tty(4).
Printed 10/17/86 3
%%index%%
na:72,82;
sy:154,444;
de:598,2429;3171,2579;
di:5750,156;6050,297;
rv:6347,245;
se:6592,354;
%%index%%000000000126