on_exit.3: Atack variables may be out of scope when exit handler is invoked

[thirdparty/man-pages.git] / man2 / getgroups.2

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.\" Modified Thu Oct 31 12:04:29 1996 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\"     Added notes on capability requirements
.\" 2008-05-03, mtk, expanded and rewrote parts of DESCRIPTION and RETURN
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.TH GETGROUPS 2 2019-03-06 "Linux" "Linux Programmer's Manual"
.SH NAME
getgroups, setgroups \- get/set list of supplementary group IDs
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.PP
.BI "int getgroups(int " size ", gid_t " list []);

.B #include <grp.h>
.PP
.BI "int setgroups(size_t " size ", const gid_t *" list );
.PP
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.PP
.BR setgroups ():
    Since glibc 2.19:
        _DEFAULT_SOURCE
    Glibc 2.19 and earlier:
        _BSD_SOURCE
.SH DESCRIPTION
.PP
.BR getgroups ()
returns the supplementary group IDs of the calling process in
.IR list .
The argument
.I size
should be set to the maximum number of items that can be stored in the
buffer pointed to by
.IR list .
If the calling process is a member of more than
.I size
supplementary groups, then an error results.
It is unspecified whether the effective group ID of the calling process
is included in the returned list.
(Thus, an application should also call
.BR getegid (2)
and add or remove the resulting value.)
.PP
If
.I size
is zero,
.I list
is not modified, but the total number of supplementary group IDs for the
process is returned.
This allows the caller to determine the size of a dynamically allocated
.I list
to be used in a further call to
.BR getgroups ().
.PP
.BR setgroups ()
sets the supplementary group IDs for the calling process.
Appropriate privileges are required (see the description of the
.BR EPERM
error, below).
The
.I size
argument specifies the number of supplementary group IDs
in the buffer pointed to by
.IR list .
A process can drop all of its supplementary groups with the call:
.PP
.in +4n
.EX
setgroups(0, NULL);
.EE
.in
.SH RETURN VALUE
On success,
.BR getgroups ()