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   getgrouplist    ( 3 )

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Имя (Name)

getgrouplist - get list of groups to which a user belongs

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Синопсис (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():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE

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Описание (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 getgrouplist(); 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.

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Возвращаемое значение (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
       getgrouplist() returns -1.  In this case, the value returned in
       *ngroups can be used to resize the buffer passed to a further
       call getgrouplist().

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Версии (Versions)

This function is present since glibc 2.2.4.

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Атрибуты (Attributes)

For an explanation of the terms used in this section, see
       attributes(7).

       ┌───────────────────────────────┬───────────────┬────────────────┐
       │Interface                      │ Attribute     │ Value          │
       ├───────────────────────────────┼───────────────┼────────────────┤
       │getgrouplist()                 │ Thread safety │ MT-Safe locale │
       └───────────────────────────────┴───────────────┴────────────────┘

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Стандарты (Conforming to)

This function is nonstandard; it appears on most BSDs.

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Ошибки (баги) (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.

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Примеры (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 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
           $ ./a.out cecilia 3
           ngroups = 3
           16 (dialout)
           33 (video)
           100 (users)

   Program source

       #include <stdio.h>
       #include <stdlib.h>
       #include <grp.h>
       #include <pwd.h>

       int
       main(int argc, char *argv[])
       {
           int ngroups;
           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]);

           gid_t *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\n",
                       ngroups);
               exit(EXIT_FAILURE);
           }

           /* Display list of retrieved groups, along with group names. */

           fprintf(stderr, "ngroups = %d\n", ngroups);
           for (int 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);
       }

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Смотри также (See also)

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

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