Examine and change blocked signals
int sigprocmask(int how, const sigset_t *set, sigset_t *oldset);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
sigprocmask(): _POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _POSIX_SOURCE
sigprocmask() is used to fetch and/or change the signal mask of the calling thread. The signal mask is the set of signals whose delivery is currently blocked for the caller (see also signal(7) for more details).
The behavior of the call is dependent on the value of how, as follows.
The set of blocked signals is the union of the current set and the set argument.
The signals in set are removed from the current set of blocked signals. It is permissible to attempt to unblock a signal which is not blocked.
The set of blocked signals is set to the argument set.
If oldset is non-NULL, the previous value of the signal mask is stored in oldset.
If set is NULL, then the signal mask is unchanged (i.e., how is ignored), but the current value of the signal mask is nevertheless returned in oldset (if it is not NULL).
The use of sigprocmask() is unspecified in a multithreaded process; see pthread_sigmask(3).
sigprocmask() returns 0 on success and -1 on error. In the event of an error, errno is set to indicate the cause.
the set or oldset argument points outside the process's allocated address space.
The value specified in how was invalid.
It is not possible to block SIGKILL or SIGSTOP. Attempts to do so are silently ignored.
Each of the threads in a process has its own signal mask.
A child created via fork(2) inherits a copy of its parent's signal mask; the signal mask is preserved across execve(2).
If SIGBUS, SIGFPE, SIGILL, or SIGSEGV are generated while they are blocked, the result is undefined, unless the signal was generated by kill(2), sigqueue(3), or raise(3).
See sigsetops(3) for details on manipulating signal sets.
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