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    Command:

    getgrouplist

    
    
    

    SYNOPSIS

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

    DESCRIPTION

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

    RETURN VALUE

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

    VERSIONS

           This function is present since glibc 2.2.4.
    
    
    

    CONFORMING TO

           This function is nonstandard; it appears on most BSDs.
    
    
    

    BUGS

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

    EXAMPLE

           The program below displays the group list for the  user  named  in  its
           first  command-line  argument.  The second command-line argument speci-
           fies the ngroups value to be supplied to getgrouplist().  The following
           shell session shows examples of the use of this program:
    
               $ ./a.out cecilia 0
               getgrouplist() returned -1; ngroups = 3
    
           main(int argc, char *argv[])
           {
               int j, ngroups;
               gid_t *groups;
               struct passwd *pw;
               struct group *gr;
    
               if (argc != 3) {
                   fprintf(stderr, "Usage: %s <user> <ngroups>\n", argv[0]);
                   exit(EXIT_FAILURE);
               }
    
               ngroups = atoi(argv[2]);
    
               groups = malloc(ngroups * sizeof (gid_t));
               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\n",
                           ngroups);
                   exit(EXIT_FAILURE);
               }
    
               /* Display list of retrieved groups, along with group names */
    
               fprintf(stderr, "ngroups = %d\n", ngroups);
               for (j = 0; j < ngroups; j++) {
                   printf("%d", groups[j]);
                   gr = getgrgid(groups[j]);
                   if (gr != NULL)
                       printf(" (%s)", gr->gr_name);
                   printf("\n");
               }
    
               exit(EXIT_SUCCESS);
           }
    
    
    

    SEE ALSO

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