GNU Info

(libc.info)Reading Persona

---

Next: Setting User ID Prev: How Change Persona Up: Users and Groups

---

Enter node , (file) or (file)node

Reading the Persona of a Process
================================

   Here are detailed descriptions of the functions for reading the user
and group IDs of a process, both real and effective.  To use these
facilities, you must include the header files `sys/types.h' and
`unistd.h'.

 - Data Type: uid_t
     This is an integer data type used to represent user IDs.  In the
     GNU library, this is an alias for `unsigned int'.

 - Data Type: gid_t
     This is an integer data type used to represent group IDs.  In the
     GNU library, this is an alias for `unsigned int'.

 - Function: uid_t getuid (void)
     The `getuid' function returns the real user ID of the process.

 - Function: gid_t getgid (void)
     The `getgid' function returns the real group ID of the process.

 - Function: uid_t geteuid (void)
     The `geteuid' function returns the effective user ID of the
     process.

 - Function: gid_t getegid (void)
     The `getegid' function returns the effective group ID of the
     process.

 - Function: int getgroups (int COUNT, gid_t *GROUPS)
     The `getgroups' function is used to inquire about the supplementary
     group IDs of the process.  Up to COUNT of these group IDs are
     stored in the array GROUPS; the return value from the function is
     the number of group IDs actually stored.  If COUNT is smaller than
     the total number of supplementary group IDs, then `getgroups'
     returns a value of `-1' and `errno' is set to `EINVAL'.

     If COUNT is zero, then `getgroups' just returns the total number
     of supplementary group IDs.  On systems that do not support
     supplementary groups, this will always be zero.

     Here's how to use `getgroups' to read all the supplementary group
     IDs:

          gid_t *
          read_all_groups (void)
          {
            int ngroups = getgroups (0, NULL);
            gid_t *groups
              = (gid_t *) xmalloc (ngroups * sizeof (gid_t));
            int val = getgroups (ngroups, groups);
            if (val < 0)
              {
                free (groups);
                return NULL;
              }
            return groups;
          }