SIGNAL

NAME

SYNOPSIS

DESCRIPTION

Signals allow the manipulation of a process from outside its domain as well as allowing the process to manipulate itself or copies of itself (children). There are two general types of signals: those that cause termination of a process and those that do not. Signals which cause termination of a program might result from an irrecoverable error or might be the result of a user at a terminal typing the `interrupt' character. Signals are used 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 result in the termination of the process receiving them 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 Fn signal function allows for a signal to be caught, to be ignored, or to generate an interrupt. These signals are defined in the file Aq Pa signal.h :

Name     Default Action     Description

SIGHUP   terminate process terminal line hangup

SIGINT terminate process interrupt program

SIGQUIT create core image quit program

SIGILL create core image illegal instruction

SIGTRAP create core image trace trap

SIGABRT create core image abort(2)

call (formerly
SIGIOT

SIGEMT         create core image     emulate instruction executed

SIGFPE      create core image floating-point exception

SIGKILL terminate process kill program

SIGBUS create core image bus error

SIGSEGV create core image segmentation violation

SIGSYS create core image system call given invalid argument

SIGPIPE terminate process write on a pipe with no reader

SIGALRM terminate process real-time timer expired

SIGTERM terminate process software termination signal

SIGURG discard signal urgent condition present on socket

SIGSTOP stop process stop (cannot be caught or ignored)

SIGTSTP stop process stop signal generated from keyboard

SIGCONT discard signal continue after stop

SIGCHLD discard signal child status has changed

SIGTTIN stop process background read attempted from control terminal

SIGTTOU stop process background write attempted to control terminal

SIGIO discard signal I/O

is possible on a descriptor (see
fcntl(2))

SIGXCPU        terminate process     cpu time limit exceeded (see

setrlimit(2))

SIGXFSZ        terminate process     file size limit exceeded (see

setrlimit(2))

SIGVTALRM      terminate process     virtual time alarm (see

setitimer(2))

SIGPROF        terminate process     profiling timer alarm (see

setitimer(2))

SIGWINCH       discard signal        Window size change

SIGINFO       discard signal status request from keyboard

SIGUSR1 terminate process User defined signal 1

SIGUSR2 terminate process User defined signal 2

The
Fa func procedure allows a user to choose the action upon receipt of a signal. To set the default action of the signal to occur as listed above, Fa func should be SIG_DFL A SIG_DFL resets the default action. To ignore the signal Fa func should be SIG_IGN This will cause subsequent instances of the signal to be ignored and pending instances to be discarded. If SIG_IGN is not used, further occurrences of the signal are automatically blocked and Fa func is called.

The handled signal is unblocked with the function returns and the process continues from where it left off when the signal occurred. Bf -symbolic Unlike previous signal facilities, the handler func() remains installed after a signal has been delivered. Ef

For some system calls, if a signal is caught while the call is executing and the call is prematurely terminated, the call is automatically restarted. (The handler is installed using the SA_RESTART flag with sigaction(2).) The affected system calls include read(2), write(2), sendto(2), recvfrom(2), sendmsg(2) and recvmsg(2) on a communications channel or a low speed device and during a ioctl(2) or wait(2). However, calls that have already committed are not restarted, but instead return a partial success (for example, a short read count).

When a process which has installed signal handlers forks, the child process inherits the signals. All caught signals may be reset to their default action by a call to the execve(2) function; ignored signals remain ignored.  

RETURN VALUES

ERRORS

Bq Er EINVAL

Sig is not a valid signal number.

Bq Er EINVAL

An attempt is made to ignore or supply a handler for SIGKILL or SIGSTOP

SEE ALSO

HISTORY

Index

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUES

ERRORS

SEE ALSO

HISTORY