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Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)signal.3 8.3 (Berkeley) 4/19/94 .\" .TH SIGNAL 3 "19 January 1997" GNO "System Calls" .SH NAME .BR signal \- simplified software signal facilities .SH SYNOPSIS .br #include .sp 1 void (*\fBsignal\fR (int \fIsig\fR, void (*\fIfunc\fR)(int, int)))(int, int); .sp 1 or in GNO's equivalent but easier to read typedef'd version: .sp 1 typedef void (*sig_t) (int, int) .sp 1 sig_t \fBsignal\fR(int \fIsig\fR, sig_t \fIfunc\fR); .SH 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 .BR 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. .LP 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. The .BR signal function allows for a signal to be caught, to be ignored, or to generate an interrupt, except for .BR SIGCONT (which cannot be blocked), and .BR SIGKILL and .BR SIGSTOP (which cannot be caught, blocked, or ignored). .LP These signals are defined in the file : .RS .nf Name Default Action Description SIGHUP termination terminal line hangup SIGINT termination interrupt program SIGQUIT termination quit program SIGILL termination illegal instruction SIGTRAP termination trace trap SIGABRT termination abort (generated by \fBabort\fR(3)) SIGEMT termination emulator trap SIGFPE termination arithmetic exception SIGKILL termination kill program SIGBUS termination bus error SIGSEGV termination segmentation fault SIGSYS termination bad argument to system call SIGPIPE termination write on a socket with no readers SIGALRM termination real-time timer expired SIGTERM termination software termination SIGURG discarded urgent condition present on socket SIGSTOP stop stop SIGTSTP stop stop signal from keyboard SIGCONT discarded continue after stop SIGCHLD discarded child status has changed SIGCLD discarded SYSV name for SIGCHLD SIGTTIN stop background read attempted SIGTTOU stop background write attempted SIGIO discarded input/output possible on a file descriptor SIGPOLL discarded SYSV name for SIGIO SIGXCPU termination exceeded CPU time limit SIGUSR1 termination user defined signal 1 SIGUSR2 termination user defined signal 2 .fi .RE .LP The .I 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, .I func should be .BR SIG_DFL . A .BR SIG_DFL resets the default action. To ignore the signal .I func should be .BR SIG_IGN . This will cause subsequent instances of the signal to be ignored and pending instances to be discarded. If .BR SIG_IGN is not used, further occurrences of the signal are automatically blocked and .I func is called. .LP The handled signal is unblocked with the function returns and the process continues from where it left off when the signal occurred. \fIUnlike previous Unix signal facilities, the handler func() remains installed after a signal has been delivered.\fR This behavior remains unchanged from GNO v2.0.4. .LP 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 affected system calls include .BR read (2), .BR write (2), .BR sendto (2), .BR recvfrom (2), .BR sendmsg (2) and .BR recvmsg (2) on a communications channel or a low speed device and during a .BR ioctl (2) or .BR wait (2). However, calls that have already committed are not restarted, but instead return a partial success (for example, a short read count). .LP When a process which has installed signal handlers forks, the child process inherits the signals. All caught signals will be reset to their default action by a call to one of the .BR execve (2) family of functions; ignored signals remain ignored. .SH NOTES As can be surmised from the prototype above, .IR func should be defined as follows: .RS .sp 1 void \fIfunc\fR(int \fIsig\fR, int \fIcode\fR) .sp 1 .RE .I sig is the signal that will invoke the handler, and .I code is additional information about the interrupt condition. Currently, .I code is always zero. The handler should probably also be compiled using the .B "#pragma databank 1" directive, in the event .I func is not in the same bank as the C global data segment .RI ( func is called with the data bank equal to the program bank). .LP Orca/C already provides a .BR signal function, but it doesn't do very much. GNO's file replaces the one that comes with Orca/C. .SH RETURN VALUES The previous action is returned on a successful call. Otherwise, \-1 is returned and the global variable .IR errno is set to indicate the error. .SH ERRORS .BR Signal will fail and no action will take place if one of the following occur: .RS .IP \fBEINVAL\fR .IR Sig is not a valid signal number. .IP \fBEINVAL\fR An attempt is made to ignore or supply a handler for .BR SIGKILL or .BR SIGSTOP . .IP \fBEINVAL\fR An attempt is made to ignore .BR SIGCONT (by default .BR SIGCONT is ignored). .SH SEE ALSO .BR kill (1), .BR execve (2), .BR fork (2), .BR kill (2), .BR sigblock (2), .BR sigsetmask (2), .BR wait (2), .BR tty (4) .SH HISTORY A .BR signal facility appeared in 4.0BSD.