SIGNAL(3C)SIGNAL(3C)NAMEsignal - simplified software signal facilities
SYNOPSIS
#include <signal.h>
(*signal(int sig, void (*func)(int)))(int);
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, etc.),
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 <sys/signal.h>. These are passed to the signal call in the
argument sig.
SIGHUP 1 hangup
SIGINT 2 interrupt
SIGQUIT 3* quit
SIGILL 4* illegal instruction
SIGTRAP 5* trace trap
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
SIGURG 16@ urgent condition present on socket
SIGSTOP 17|+'stop (cannot be caught or ignored)
SIGTSTP 18|+'stop signal generated from keyboard
SIGCONT 19@ continue after stop
SIGCHLD 20@ child status has changed
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))
SIGWINCH 28@ Window size change
SIGUSR1 30 User defined signal 1
SIGUSR2 31 User defined signal 2
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 occurrences 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. 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 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.
RETURN VALUE
The previous action is returned on a successful call. Otherwise, -1 is
returned and errno is set to indicate the error.
ERRORS
Signal will fail and no action will take place if one of the following
occur:
[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).
SEE ALSOkill(1), ptrace(2), kill(2), sigvec(2), sigblock(2), sigsetmask(2),
sigpause(2), sigstack(2), setjmp(3), tty(4)4th Berkeley Distribution January 26, 1989 SIGNAL(3C)