1GETGROUPS(3P) POSIX Programmer's Manual GETGROUPS(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 getgroups — get supplementary group IDs
13
15 #include <unistd.h>
16 int getgroups(int gidsetsize, gid_t grouplist[]);
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20 The getgroups() function shall fill in the array grouplist with the
21 current supplementary group IDs of the calling process. It is implemen‐
22 tation-defined whether getgroups() also returns the effective group ID
23 in the grouplist array.
24 The gidsetsize argument specifies the number of elements in the array
26 grouplist. The actual number of group IDs stored in the array shall be
27 returned. The values of array entries with indices greater than or
28 equal to the value returned are undefined.
29 If gidsetsize is 0, getgroups() shall return the number of group IDs
31 that it would otherwise return without modifying the array pointed to
32 by grouplist.
33 If the effective group ID of the process is returned with the supple‐
35 mentary group IDs, the value returned shall always be greater than or
36 equal to one and less than or equal to the value of {NGROUPS_MAX}+1.
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39 Upon successful completion, the number of supplementary group IDs shall
40 be returned. A return value of -1 indicates failure and errno shall be
41 set to indicate the error.
42
44 The getgroups() function shall fail if:
45 EINVAL The gidsetsize argument is non-zero and less than the number of
47 group IDs that would have been returned.
48 The following sections are informative.
50
52 Getting the Supplementary Group IDs of the Calling Process
53 The following example places the current supplementary group IDs of the
54 calling process into the group array.
55 #include <sys/types.h>
58 #include <unistd.h>
59 ...
60 gid_t *group;
61 int nogroups;
62 long ngroups_max;
63 ngroups_max = sysconf(_SC_NGROUPS_MAX) + 1;
65 group = (gid_t *)malloc(ngroups_max *sizeof(gid_t));
66 ngroups = getgroups(ngroups_max, group);
68
70 None.
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73 The related function setgroups() is a privileged operation and there‐
74 fore is not covered by this volume of POSIX.1‐2017.
75 As implied by the definition of supplementary groups, the effective
77 group ID may appear in the array returned by getgroups() or it may be
78 returned only by getegid(). Duplication may exist, but the application
79 needs to call getegid() to be sure of getting all of the information.
80 Various implementation variations and administrative sequences cause
81 the set of groups appearing in the result of getgroups() to vary in
82 order and as to whether the effective group ID is included, even when
83 the set of groups is the same (in the mathematical sense of ``set'').
84 (The history of a process and its parents could affect the details of
85 the result.)
86 Application developers should note that {NGROUPS_MAX} is not necessar‐
88 ily a constant on all implementations.
89
91 None.
92
94 getegid(), setgid()
95 The Base Definitions volume of POSIX.1‐2017, <sys_types.h>, <unistd.h>
97
99 Portions of this text are reprinted and reproduced in electronic form
100 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
101 table Operating System Interface (POSIX), The Open Group Base Specifi‐
102 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
103 Electrical and Electronics Engineers, Inc and The Open Group. In the
104 event of any discrepancy between this version and the original IEEE and
105 The Open Group Standard, the original IEEE and The Open Group Standard
106 is the referee document. The original Standard can be obtained online
107 at http://www.opengroup.org/unix/online.html .
108 Any typographical or formatting errors that appear in this page are
110 most likely to have been introduced during the conversion of the source
111 files to man page format. To report such errors, see https://www.ker‐
112 nel.org/doc/man-pages/reporting_bugs.html .
113IEEE/The Open Group 2017 GETGROUPS(3P)