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#include <signal.h>
(*signal(int sig, void (*func)(int)))(int);
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.
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Created by unroff & hp-tools. © somebody (See intro for details). All Rights Reserved. Last modified 11/5/97