signal(2)signal(2)NAMEsignal - Modifies signal functions
SYNOPSIS
#include <signal.h>
void (*signal(
int sig,
void (*function)(int)) (int) );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
signal(): XPG4, XPG4-UNIX
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Defines the signal. All signals are valid with the exception of
SIGKILL and SIGSTOP. Specifies the address of a signal handler.
DESCRIPTION
The signal function provides compatibility for older versions of the
operating system whose function is a subset of the sigaction function.
The signal function sets the action associated with a signal. The func‐
tion parameter uses the values SIG_DFL, SIG_IGN, or it can point to an
address of a signal handler.
A SIG_DFL value specifies the default action that is to be taken when
the signal is delivered. A value of SIG_IGN specifies that the signal
has no effect on the receiving process. A pointer to a function
requests that the signal be caught; that is, the signal should cause
the function to be called. These actions are more fully described in
the <signal.h> file.
NOTES
The sigaction() function provides a more comprehensive and reliable
mechanism for controlling signals and is recommended instead of sig‐
nal() for new applications.
[Tru64 UNIX] The effect of calling the signal function behavior dif‐
fers depending on whether the calling program is linked with either of
the special libraries, libbsd or libsys5, which supply BSD or System V
signaling characteristics respectively. If neither library is used, the
behavior is the same as that of the sigaction function with all the
flags set to 0 (zero). If the libsys5 library is used (through compi‐
lation with the -lsys5 switch), then the specified signal is not
blocked from delivery when the handler is entered, and the disposition
of the signal reverts to SIG_DFL when the signal is delivered. If the
libbsd library or the bsd_signal() function is used, the behavior is
the same as that of the sigaction() function with the SA_RESTART flag
set.
[Tru64 UNIX] When compiled in the X/Open UNIX environment, calls to
the signal() function are internally renamed by prepending _E to the
function name. When you are debugging a module that includes the libc
version of the signal() function and for which _XOPEN_SOURCE_EXTENDED
has been defined, use _Esignal to refer to the signal() call. See
standards(5) for information on when the _XOPEN_SOURCE_EXTENDED macro
is defined.
RETURN VALUES
Upon successful completion of the signal function, the value of the
previous signal action is returned. Otherwise, SIG_ERR is returned and
errno is set to indicate the error.
ERRORS
The signal() function sets errno to the specified values for the fol‐
lowing conditions: The sig parameter is not a valid signal number or an
attempt was made to catch a signal that cannot be caught or to ignore a
signal that cannot be ignored.
SEE ALSO
Commands: kill(1)
Functions: acct(2), bsd_signal(2), exit(2), kill(2), pause(3),
ptrace(2), setjmp(3), sigaction(2), sigblock(2), sigpause(3), sigproc‐
mask(2), sigstack(2), sigsuspend(2), sigvec(2), umask(2), wait(2)
Files: signal(4)
Standards: standards(5)signal(2)
