Manpages - getgrnam.3

getgrnam, getgrnam_r, getgrgid, getgrgid_r - get group file entry

  #include <sys/types.h>
  #include <grp.h>

  struct group *getgrnam(const char *name);
  struct group *getgrgid(gid_t gid);

  int getgrnam_r(const char *restrict name",structgroup*restrict"grp,
   char *restrict buf, size_t buflen,
   struct group **restrict result);
  int getgrgid_r(gid_t gid, struct group *restrict grp,
   char *restrict buf, size_t buflen,
   struct group **restrict result);

Feature Test Macro Requirements for glibc (see *feature_test_macros*(7)):

*getgrnam_r*(), *getgrgid_r*():

      _POSIX_C_SOURCE
          || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

The *getgrnam*() function returns a pointer to a structure containing the broken-out fields of the record in the group database (e.g., the local group file /etc/group, NIS, and LDAP) that matches the group name name.

The *getgrgid*() function returns a pointer to a structure containing the broken-out fields of the record in the group database that matches the group ID gid.

The group structure is defined in <grp.h> as follows:

  struct group {
      char   *gr_name;        /* group name */
      char   *gr_passwd;      /* group password */
      gid_t   gr_gid;         /* group ID */
      char  **gr_mem;         /* NULL-terminated array of pointers
                                 to names of group members */
  };

For more information about the fields of this structure, see *group*(5).

The *getgrnam_r*() and *getgrgid_r*() functions obtain the same information as *getgrnam*() and *getgrgid*(), but store the retrieved group structure in the space pointed to by grp. The string fields pointed to by the members of the group structure are stored in the buffer buf of size buflen. A pointer to the result (in case of success) or NULL (in case no entry was found or an error occurred) is stored in *result.

The call

sysconf(_SC_GETGR_R_SIZE_MAX)

returns either -1, without changing errno, or an initial suggested size for buf. (If this size is too small, the call fails with ERANGE, in which case the caller can retry with a larger buffer.)

The *getgrnam*() and *getgrgid*() functions return a pointer to a group structure, or NULL if the matching entry is not found or an error occurs. If an error occurs, errno is set to indicate the error. If one wants to check errno after the call, it should be set to zero before the call.

The return value may point to a static area, and may be overwritten by subsequent calls to *getgrent*(3), *getgrgid*(), or *getgrnam*(). (Do not pass the returned pointer to *free*(3).)

On success, *getgrnam_r*() and *getgrgid_r*() return zero, and set *result to grp. If no matching group record was found, these functions return 0 and store NULL in *result. In case of error, an error number is returned, and NULL is stored in *result.

0 or ENOENT or ESRCH or EBADF or EPERM or …

The given name or gid was not found.

EINTR

A signal was caught; see *signal*(7).

EIO

I/O error.

EMFILE

The per-process limit on the number of open file descriptors has been reached.

ENFILE

The system-wide limit on the total number of open files has been reached.

ENOMEM

Insufficient memory to allocate group structure.

ERANGE

Insufficient buffer space supplied.

/etc/group

local group database file

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

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

The formulation given above under “RETURN VALUE” is from POSIX.1. It does not call “not found” an error, hence does not specify what value errno might have in this situation. But that makes it impossible to recognize errors. One might argue that according to POSIX errno should be left unchanged if an entry is not found. Experiments on various UNIX-like systems show that lots of different values occur in this situation: 0, ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM, and probably others.

*endgrent*(3), *fgetgrent*(3), *getgrent*(3), *getpwnam*(3), *setgrent*(3), *group*(5)

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