man2/getgroups.2

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  25 .\" Modified Thu Oct 31 12:04:29 1996 by Eric S. Raymond <esr@thyrsus.com>
  26 .\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
  27 .\"     Added notes on capability requirements
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  29 .TH GETGROUPS 2 2004-05-27 "Linux 2.6.6" "Linux Programmer's Manual"
  30 .SH NAME
  31 getgroups, setgroups \- get/set list of supplementary group IDs
  32 .SH SYNOPSIS
  33 .B #include <sys/types.h>
  34 .br
  35 .B #include <unistd.h>
  36 .sp
  37 .BI "int getgroups(int " size ", gid_t " list []);
  38 .sp
  39 .B #include <grp.h>
  40 .sp
  41 .BI "int setgroups(size_t " size ", const gid_t *" list );
  42 .SH DESCRIPTION
  43 .TP
  44 .BR getgroups ()
  45 Up to
  46 .I size
  47 supplementary group IDs (of the calling process) are returned in
  48 .IR list .
  49 It is unspecified whether the effective group ID of the calling process
  50 is included in the returned list.
  51 (Thus, an application should also call
  52 .BR getegid (2)
  53 and add or remove the resulting value.)
  54 If
  55 .I size
  56 is zero,
  57 .I list
  58 is not modified, but the total number of supplementary group IDs for the
  59 process is returned.
  60 .TP
  61 .BR setgroups ()
  62 Sets the supplementary group IDs for the process.
  63 Appropriate privileges (Linux: the
  64 .B CAP_SETGID
  65 capability) are required.
  66 .SH "RETURN VALUE"
  67 .TP
  68 .BR getgroups ()
  69 On success, the number of supplementary group IDs is returned.
  70 On error, \-1 is returned, and
  71 .I errno
  72 is set appropriately.
  73 .TP
  74 .BR setgroups ()
  75 On success, zero is returned.
  76 On error, \-1 is returned, and
  77 .I errno
  78 is set appropriately.
  79 .SH ERRORS
  80 .TP
  81 .B EFAULT
  82 .I list
  83 has an invalid address.
  84 .TP
  85 .B EINVAL
  86 For
  87 .BR setgroups (),
  88 .I size
  89 is greater than
  90 .B NGROUPS
  91 (32 for Linux 2.0.32).
  92 For
  93 .BR getgroups (),
  94 .I size
  95 is less than the number of supplementary group IDs, but is not zero.
  96 .TP
  97 .B EPERM
  98 The calling process has insufficient privilege to call
  99 .BR setgroups ().
 100 .SH NOTES
 101 A process can have up to at least NGROUPS_MAX supplementary group IDs
 102 in addition to the effective group ID.
 103 The set of supplementary group IDs
 104 is inherited from the parent process and may be changed using
 105 .BR setgroups ().
 106 The maximum number of supplementary group IDs can be found using
 107 .BR sysconf (3):
 108 .nf
 109
 110     long ngroups_max;
 111     ngroups_max = sysconf(_SC_NGROUPS_MAX);
 112
 113 .fi
 114 The maximal return value of
 115 .BR getgroups ()
 116 cannot be larger than one more than the value obtained this way.
 117 .LP
 118 The prototype for
 119 .BR setgroups ()
 120 is only available if
 121 .B _BSD_SOURCE
 122 is defined.
 123 .SH "CONFORMING TO"
 124 SVr4, 4.3BSD.
 125 The
 126 .BR getgroups ()
 127 function is in POSIX.1-2001.
 128 Since
 129 .BR setgroups ()
 130 requires privilege, it is not covered by POSIX.1-2001.
 131 .SH "SEE ALSO"
 132 .BR getgid (2),
 133 .BR setgid (2),
 134 .BR initgroups (3),
 135 .BR capabilities (7)