1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
'\" t
.\" Copyright (C) 2008, Linux Foundation, written by Michael Kerrisk
.\" <mtk.manpages@gmail.com>
.\"
.\" A few pieces remain from an earlier version written in
.\" 2002 by Walter Harms (walter.harms@informatik.uni-oldenburg.de)
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH getgrouplist 3 2023-02-05 "Linux man-pages 6.03"
.SH NAME
getgrouplist \- get list of groups to which a user belongs
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <grp.h>
.PP
.BI "int getgrouplist(const char *" user ", gid_t " group ,
.BI " gid_t *" groups ", int *" ngroups );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR getgrouplist ():
.nf
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE
.fi
.SH DESCRIPTION
The
.BR getgrouplist ()
function scans the group database (see
.BR group (5))
to obtain the list of groups that
.I user
belongs to.
Up to
.I *ngroups
of these groups are returned in the array
.IR groups .
.PP
If it was not among the groups defined for
.I user
in the group database, then
.I group
is included in the list of groups returned by
.BR getgrouplist ();
typically this argument is specified as the group ID from
the password record for
.IR user .
.PP
The
.I ngroups
argument is a value-result argument:
on return it always contains the number of groups found for
.IR user ,
including
.IR group ;
this value may be greater than the number of groups stored in
.IR groups .
.SH RETURN VALUE
If the number of groups of which
.I user
is a member is less than or equal to
.IR *ngroups ,
then the value
.I *ngroups
is returned.
.PP
If the user is a member of more than
.I *ngroups
groups, then
.BR getgrouplist ()
returns \-1.
In this case, the value returned in
.I *ngroups
can be used to resize the buffer passed to a further call to
.BR getgrouplist ().
.SH VERSIONS
This function is present since glibc 2.2.4.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface Attribute Value
T{
.BR getgrouplist ()
T} Thread safety MT-Safe locale
.TE
.hy
.ad
.sp 1
.SH STANDARDS
This function is nonstandard; it appears on most BSDs.
.SH BUGS
Before glibc 2.3.3,
the implementation of this function contains a buffer-overrun bug:
it returns the complete list of groups for
.I user
in the array
.IR groups ,
even when the number of groups exceeds
.IR *ngroups .
.SH EXAMPLES
The program below displays the group list for the user named in its
first command-line argument.
The second command-line argument specifies the
.I ngroups
value to be supplied to
.BR getgrouplist ().
The following shell session shows examples of the use of this program:
.PP
.in +4n
.EX
.RB "$" " ./a.out cecilia 0"
getgrouplist() returned \-1; ngroups = 3
.RB "$" " ./a.out cecilia 3"
ngroups = 3
16 (dialout)
33 (video)
100 (users)
.EE
.in
.SS Program source
\&
.\" SRC BEGIN (getgrouplist.c)
.EX
#include <grp.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
int ngroups;
struct passwd *pw;
struct group *gr;
gid_t *groups;
if (argc != 3) {
fprintf(stderr, "Usage: %s <user> <ngroups>\en", argv[0]);
exit(EXIT_FAILURE);
}
ngroups = atoi(argv[2]);
groups = malloc(sizeof(*groups) * ngroups);
if (groups == NULL) {
perror("malloc");
exit(EXIT_FAILURE);
}
/* Fetch passwd structure (contains first group ID for user). */
pw = getpwnam(argv[1]);
if (pw == NULL) {
perror("getpwnam");
exit(EXIT_SUCCESS);
}
/* Retrieve group list. */
if (getgrouplist(argv[1], pw\->pw_gid, groups, &ngroups) == \-1) {
fprintf(stderr, "getgrouplist() returned \-1; ngroups = %d\en",
ngroups);
exit(EXIT_FAILURE);
}
/* Display list of retrieved groups, along with group names. */
fprintf(stderr, "ngroups = %d\en", ngroups);
for (size_t j = 0; j < ngroups; j++) {
printf("%d", groups[j]);
gr = getgrgid(groups[j]);
if (gr != NULL)
printf(" (%s)", gr\->gr_name);
printf("\en");
}
exit(EXIT_SUCCESS);
}
.EE
.\" SRC END
.SH SEE ALSO
.BR getgroups (2),
.BR setgroups (2),
.BR getgrent (3),
.BR group_member (3),
.BR group (5),
.BR passwd (5)
|
