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

6       getgrouplist - get list of groups to which a user belongs
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SYNOPSIS

9       #include <grp.h>
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11       int getgrouplist(const char *user, gid_t group,
12                        gid_t *groups, int *ngroups);
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14   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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16       getgrouplist(): _BSD_SOURCE
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DESCRIPTION

19       The  getgrouplist() function scans the group database (see group(5)) to
20       obtain the list of groups that user belongs  to.   Up  to  *ngroups  of
21       these groups are returned in the array groups.
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23       If  it was not among the groups defined for user in the group database,
24       then group is included in the  list  of  groups  returned  by  getgrou‐
25       plist();  typically this argument is specified as the group ID from the
26       password record for user.
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28       The ngroups argument is a value-result argument: on  return  it  always
29       contains  the  number  of  groups found for user, including group; this
30       value may be greater than the number of groups stored in groups.
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RETURN VALUE

33       If the number of groups of which user is a member is less than or equal
34       to *ngroups, then the value *ngroups is returned.
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36       If  the  user  is  a member of more than *ngroups groups, then getgrou‐
37       plist() returns -1.  In this case the value returned in *ngroups can be
38       used to resize the buffer passed to a further call getgrouplist().
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VERSIONS

41       This function is present since glibc 2.2.4.
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CONFORMING TO

44       This function is nonstandard; it appears on most BSDs.
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BUGS

47       In  glibc  versions  before  2.3.3, the implementation of this function
48       contains a buffer-overrun bug: it returns the complete list  of  groups
49       for  user  in  the array groups, even when the number of groups exceeds
50       *ngroups.
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EXAMPLE

53       The program below displays the group list for the  user  named  in  its
54       first  command-line  argument.  The second command-line argument speci‐
55       fies the ngroups value to be supplied to getgrouplist().  The following
56       shell session shows examples of the use of this program:
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58           $ ./a.out cecilia 0
59           getgrouplist() returned -1; ngroups = 3
60           $ ./a.out cecilia 3
61           ngroups = 3
62           16 (dialout)
63           33 (video)
64           100 (users)
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66   Program source
67
68       #include <stdio.h>
69       #include <stdlib.h>
70       #include <grp.h>
71       #include <pwd.h>
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73       int
74       main(int argc, char *argv[])
75       {
76           int j, ngroups;
77           gid_t *groups;
78           struct passwd *pw;
79           struct group *gr;
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81           if (argc != 3) {
82               fprintf(stderr, "Usage: %s <user> <ngroups>\n", argv[0]);
83               exit(EXIT_FAILURE);
84           }
85
86           ngroups = atoi(argv[2]);
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88           groups = malloc(ngroups * sizeof (gid_t));
89           if (groups == NULL) {
90               perror("malloc");
91               exit(EXIT_FAILURE);
92           }
93
94           /* Fetch passwd structure (contains first group ID for user) */
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96           pw = getpwnam(argv[1]);
97           if (pw == NULL) {
98               perror("getpwnam");
99               exit(EXIT_SUCCESS);
100           }
101
102           /* Retrieve group list */
103
104           if (getgrouplist(argv[1], pw->pw_gid, groups, &ngroups) == -1) {
105               fprintf(stderr, "getgrouplist() returned -1; ngroups = %d\n",
106                       ngroups);
107            exit(EXIT_FAILURE);
108           }
109
110           /* Display list of retrieved groups, along with group names */
111
112           fprintf(stderr, "ngroups = %d\n", ngroups);
113           for (j = 0; j < ngroups; j++) {
114               printf("%d", groups[j]);
115               gr = getgrgid(groups[j]);
116               if (gr != NULL)
117                   printf(" (%s)", gr->gr_name);
118               printf("\n");
119           }
120
121           exit(EXIT_SUCCESS);
122       }
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SEE ALSO

125       getgroups(2), setgroups(2), getgrent(3), group(5), passwd(5)
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COLOPHON

128       This  page  is  part of release 3.25 of the Linux man-pages project.  A
129       description of the project, and information about reporting  bugs,  can
130       be found at http://www.kernel.org/doc/man-pages/.
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134GNU                               2008-07-03                   GETGROUPLIST(3)
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