sighold(3)

1sigset(3)                  Library Functions Manual                  sigset(3)
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NAME

6       sigset, sighold, sigrelse, sigignore - System V signal API
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <signal.h>
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14       typedef void (*sighandler_t)(int);
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16       [[deprecated]] sighandler_t sigset(int sig, sighandler_t disp);
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18       [[deprecated]] int sighold(int sig);
19       [[deprecated]] int sigrelse(int sig);
20       [[deprecated]] int sigignore(int sig);
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22   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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24       sigset(), sighold(), sigrelse(), sigignore():
25           _XOPEN_SOURCE >= 500
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DESCRIPTION

28       These  functions are provided in glibc as a compatibility interface for
29       programs that make use of the historical System V signal API.  This API
30       is  obsolete:  new applications should use the POSIX signal API (sigac‐
31       tion(2), sigprocmask(2), etc.)
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33       The sigset() function modifies the disposition of the signal sig.   The
34       disp  argument  can be the address of a signal handler function, or one
35       of the following constants:
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37       SIG_DFL
38              Reset the disposition of sig to the default.
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40       SIG_IGN
41              Ignore sig.
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43       SIG_HOLD
44              Add sig to the process's signal mask, but leave the  disposition
45              of sig unchanged.
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47       If disp specifies the address of a signal handler, then sig is added to
48       the process's signal mask during execution of the handler.
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50       If disp was specified as a value other than SIG_HOLD, then sig  is  re‐
51       moved from the process's signal mask.
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53       The dispositions for SIGKILL and SIGSTOP cannot be changed.
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55       The sighold() function adds sig to the calling process's signal mask.
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57       The  sigrelse()  function removes sig from the calling process's signal
58       mask.
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60       The sigignore() function sets the disposition of sig to SIG_IGN.
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RETURN VALUE

63       On success, sigset() returns SIG_HOLD if sig  was  blocked  before  the
64       call, or the signal's previous disposition if it was not blocked before
65       the call.  On error, sigset() returns -1, with errno  set  to  indicate
66       the error.  (But see BUGS below.)
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68       The  sighold(),  sigrelse(), and sigignore() functions return 0 on suc‐
69       cess; on error, these functions return -1 and set errno to indicate the
70       error.
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ERRORS

73       For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).
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75       For sighold() and sigrelse() see the ERRORS under sigprocmask(2).
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77       For sigignore(), see the errors under sigaction(2).
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ATTRIBUTES

80       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
81       tributes(7).
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83       ┌────────────────────────────────────────────┬───────────────┬─────────┐
84       │Interface                                   │ Attribute     │ Value   │
85       ├────────────────────────────────────────────┼───────────────┼─────────┤
86       │sigset(), sighold(), sigrelse(),            │ Thread safety │ MT-Safe │
87       │sigignore()                                 │               │         │
88       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

91       POSIX.1-2008.
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93       sighandler_t
94              GNU.  POSIX.1 uses the same type but without a typedef.
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HISTORY

97       glibc  2.1.  SVr4, POSIX.1-2001.  POSIX.1-2008 marks these functions as
98       obsolete,  recommending  the  use  of   sigaction(2),   sigprocmask(2),
99       pthread_sigmask(3), and sigsuspend(2) instead.
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NOTES

102       The  sigset()  function provides reliable signal handling semantics (as
103       when calling sigaction(2) with sa_mask equal to 0).
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105       On System V, the signal() function provides  unreliable  semantics  (as
106       when   calling  sigaction(2)  with  sa_mask  equal  to  SA_RESETHAND  |
107       SA_NODEFER).    On   BSD,   signal()   provides   reliable   semantics.
108       POSIX.1-2001   leaves  these  aspects  of  signal()  unspecified.   See
109       signal(2) for further details.
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111       In order to wait for a  signal,  BSD  and  System  V  both  provided  a
112       function  named sigpause(3), but this function has a different argument
113       on the two systems.  See sigpause(3) for details.
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BUGS

116       Before glibc 2.2, sigset() did not unblock sig if disp was specified as
117       a value other than SIG_HOLD.
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119       Before  glibc  2.5,  sigset()  does  not  correctly return the previous
120       disposition of the signal in two cases.  First, if disp is specified as
121       SIG_HOLD, then a successful sigset() always returns SIG_HOLD.  Instead,
122       it should return the previous disposition of  the  signal  (unless  the
123       signal  was  blocked,  in  which  case  SIG_HOLD  should  be returned).
124       Second, if the signal is currently blocked, then the return value of  a
125       successful   sigset()   should  be  SIG_HOLD.   Instead,  the  previous
126       disposition of the signal is returned.  These problems have been  fixed
127       since glibc 2.5.
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