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| .TH SIGSET 3 2021-03-22 "Linux" "Linux Programmer's Manual" |
| .SH NAME |
| sigset, sighold, sigrelse, sigignore \- System V signal API |
| .SH SYNOPSIS |
| .nf |
| .B #include <signal.h> |
| .PP |
| .B typedef void (*sighandler_t)(int); |
| .PP |
| .BI "sighandler_t sigset(int " sig ", sighandler_t " disp ); |
| .PP |
| .BI "int sighold(int " sig ); |
| .BI "int sigrelse(int " sig ); |
| .BI "int sigignore(int " sig ); |
| .fi |
| .PP |
| .RS -4 |
| Feature Test Macro Requirements for glibc (see |
| .BR feature_test_macros (7)): |
| .RE |
| .PP |
| .BR sigset (), |
| .BR sighold (), |
| .BR sigrelse (), |
| .BR sigignore (): |
| .nf |
| _XOPEN_SOURCE >= 500 |
| .\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED |
| .fi |
| .SH DESCRIPTION |
| These functions are provided in glibc as a compatibility interface |
| for programs that make use of the historical System V signal API. |
| This API is obsolete: new applications should use the POSIX signal API |
| .RB ( sigaction (2), |
| .BR sigprocmask (2), |
| etc.) |
| .PP |
| The |
| .BR sigset () |
| function modifies the disposition of the signal |
| .IR sig . |
| The |
| .I disp |
| argument can be the address of a signal handler function, |
| or one of the following constants: |
| .TP |
| .B SIG_DFL |
| Reset the disposition of |
| .I sig |
| to the default. |
| .TP |
| .B SIG_IGN |
| Ignore |
| .IR sig . |
| .TP |
| .B SIG_HOLD |
| Add |
| .I sig |
| to the process's signal mask, but leave the disposition of |
| .I sig |
| unchanged. |
| .PP |
| If |
| .I disp |
| specifies the address of a signal handler, then |
| .I sig |
| is added to the process's signal mask during execution of the handler. |
| .PP |
| If |
| .I disp |
| was specified as a value other than |
| .BR SIG_HOLD , |
| then |
| .I sig |
| is removed from the process's signal mask. |
| .PP |
| The dispositions for |
| .B SIGKILL |
| and |
| .B SIGSTOP |
| cannot be changed. |
| .PP |
| The |
| .BR sighold () |
| function adds |
| .I sig |
| to the calling process's signal mask. |
| .PP |
| The |
| .BR sigrelse () |
| function removes |
| .I sig |
| from the calling process's signal mask. |
| .PP |
| The |
| .BR sigignore () |
| function sets the disposition of |
| .I sig |
| to |
| .BR SIG_IGN . |
| .SH RETURN VALUE |
| On success, |
| .BR sigset () |
| returns |
| .B SIG_HOLD |
| if |
| .I sig |
| was blocked before the call, |
| or the signal's previous disposition |
| if it was not blocked before the call. |
| On error, |
| .BR sigset () |
| returns \-1, with |
| .I errno |
| set to indicate the error. |
| (But see BUGS below.) |
| .PP |
| The |
| .BR sighold (), |
| .BR sigrelse (), |
| and |
| .BR sigignore () |
| functions return 0 on success; on error, these functions return \-1 and set |
| .I errno |
| to indicate the error. |
| .SH ERRORS |
| For |
| .BR sigset () |
| see the ERRORS under |
| .BR sigaction (2) |
| and |
| .BR sigprocmask (2). |
| .PP |
| For |
| .BR sighold () |
| and |
| .BR sigrelse () |
| see the ERRORS under |
| .BR sigprocmask (2). |
| .PP |
| For |
| .BR sigignore (), |
| see the errors under |
| .BR sigaction (2). |
| .SH ATTRIBUTES |
| For an explanation of the terms used in this section, see |
| .BR attributes (7). |
| .ad l |
| .nh |
| .TS |
| allbox; |
| lbx lb lb |
| l l l. |
| Interface Attribute Value |
| T{ |
| .BR sigset (), |
| .BR sighold (), |
| .BR sigrelse (), |
| .BR sigignore () |
| T} Thread safety MT-Safe |
| .TE |
| .hy |
| .ad |
| .sp 1 |
| .SH CONFORMING TO |
| SVr4, POSIX.1-2001, POSIX.1-2008. |
| These functions are obsolete: do not use them in new programs. |
| POSIX.1-2008 marks |
| .BR sighold (), |
| .BR sigignore (), |
| .BR sigpause (3), |
| .BR sigrelse (), |
| and |
| .BR sigset () |
| as obsolete, recommending the use of |
| .BR sigaction (2), |
| .BR sigprocmask (2), |
| .BR pthread_sigmask (3), |
| and |
| .BR sigsuspend (2) |
| instead. |
| .SH NOTES |
| These functions appeared in glibc version 2.1. |
| .PP |
| The |
| .I sighandler_t |
| type is a GNU extension; it is used on this page only to make the |
| .BR sigset () |
| prototype more easily readable. |
| .PP |
| The |
| .BR sigset () |
| function provides reliable signal handling semantics (as when calling |
| .BR sigaction (2) |
| with |
| .I sa_mask |
| equal to 0). |
| .PP |
| On System V, the |
| .BR signal () |
| function provides unreliable semantics (as when calling |
| .BR sigaction (2) |
| with |
| .I sa_mask |
| equal to |
| .IR "SA_RESETHAND | SA_NODEFER" ). |
| On BSD, |
| .BR signal () |
| provides reliable semantics. |
| POSIX.1-2001 leaves these aspects of |
| .BR signal () |
| unspecified. |
| See |
| .BR signal (2) |
| for further details. |
| .PP |
| In order to wait for a signal, |
| BSD and System V both provided a function named |
| .BR sigpause (3), |
| but this function has a different argument on the two systems. |
| See |
| .BR sigpause (3) |
| for details. |
| .SH BUGS |
| In versions of glibc before 2.2, |
| .BR sigset () |
| did not unblock |
| .I sig |
| if |
| .I disp |
| was specified as a value other than |
| .BR SIG_HOLD . |
| .PP |
| In versions of glibc before 2.5, |
| .BR sigset () |
| does not correctly return the previous disposition of the signal |
| in two cases. |
| First, if |
| .I disp |
| is specified as |
| .BR SIG_HOLD , |
| then a successful |
| .BR sigset () |
| always returns |
| .BR SIG_HOLD . |
| Instead, it should return the previous disposition of the signal |
| (unless the signal was blocked, in which case |
| .B SIG_HOLD |
| should be returned). |
| Second, if the signal is currently blocked, then |
| the return value of a successful |
| .BR sigset () |
| should be |
| .BR SIG_HOLD . |
| Instead, the previous disposition of the signal is returned. |
| These problems have been fixed since glibc 2.5. |
| .\" See http://sourceware.org/bugzilla/show_bug.cgi?id=1951 |
| .SH SEE ALSO |
| .BR kill (2), |
| .BR pause (2), |
| .BR sigaction (2), |
| .BR signal (2), |
| .BR sigprocmask (2), |
| .BR raise (3), |
| .BR sigpause (3), |
| .BR sigvec (3), |
| .BR signal (7) |