sighold(3)

1SIGSET(3)                  Linux Programmer's Manual                 SIGSET(3)
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NAME

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

9       #include <signal.h>
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11       typedef void (*sighandler_t)(int);
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13       sighandler_t sigset(int sig, sighandler_t disp);
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15       int sighold(int sig);
16       int sigrelse(int sig);
17       int sigignore(int sig);
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19   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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21       sigset(), sighold(), sigrelse(), sigignore():
22           _XOPEN_SOURCE >= 500
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DESCRIPTION

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27       is  obsolete:  new applications should use the POSIX signal API (sigac‐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

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

70       For sigset() see the ERRORS under sigaction(2) and sigprocmask(2).
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72       For sighold() and sigrelse() see the ERRORS under sigprocmask(2).
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74       For sigignore(), see the errors under sigaction(2).
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ATTRIBUTES

77       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
78       tributes(7).
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80       ┌────────────────────────────────────────────┬───────────────┬─────────┐
81       │Interface                                   │ Attribute     │ Value   │
82       ├────────────────────────────────────────────┼───────────────┼─────────┤
83       │sigset(), sighold(), sigrelse(),            │ Thread safety │ MT-Safe │
84       │sigignore()                                 │               │         │
85       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

88       SVr4, POSIX.1-2001, POSIX.1-2008.  These functions are obsolete: do not
89       use them in new programs.  POSIX.1-2008 marks  sighold(),  sigignore(),
90       sigpause(3), sigrelse(), and sigset() as obsolete, recommending the use
91       of sigaction(2), sigprocmask(2), pthread_sigmask(3), and  sigsuspend(2)
92       instead.
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NOTES

95       These functions appeared in glibc version 2.1.
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97       The  sighandler_t type is a GNU extension; it is used on this page only
98       to make the sigset() prototype more easily readable.
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100       The sigset() function provides reliable signal handling  semantics  (as
101       when calling sigaction(2) with sa_mask equal to 0).
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103       On  System  V,  the signal() function provides unreliable semantics (as
104       when calling sigaction(2) with sa_mask equal to SA_RESETHAND | SA_NODE‐
105       FER).   On  BSD,  signal()  provides  reliable semantics.  POSIX.1-2001
106       leaves these aspects of signal() unspecified.  See signal(2)  for  fur‐
107       ther details.
108
109       In  order  to wait for a signal, BSD and System V both provided a func‐
110       tion named sigpause(3), but this function has a different  argument  on
111       the two systems.  See sigpause(3) for details.
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BUGS

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

132       This  page  is  part of release 5.13 of the Linux man-pages project.  A
133       description of the project, information about reporting bugs,  and  the
134       latest     version     of     this    page,    can    be    found    at
135       https://www.kernel.org/doc/man-pages/.
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139Linux                             2021-03-22                         SIGSET(3)