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| Standard C Library Functions | getgrnam(3C) |
| | getgrnam, getgrnam_r, getgrent, getgrent_r, getgrgid, getgrgid_r, setgrent, endgrent, fgetgrent, fgetgrent_r - group database entry functions |
SYNOPSIS
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#include <grp.h> struct group *getgrnam(const char *name); |
| | struct group *getgrnam_r(const char *name, struct group *grp, char *buffer, int bufsize); |
| | struct group *getgrent(void); |
| | struct group *getgrent_r(struct group *grp, char *buffer, int bufsize); |
| | struct group *getgrgid(gid_t gid); |
| | struct group *getgrgid_r(gid_t gid, struct group *grp, char *buffer, int bufsize); |
| | struct group *fgetgrent(FILE *f); |
| | struct group *fgetgrent_r(FILE *f, struct group *grp, char *buffer, int bufsize); |
POSIX
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cc [ flag... ] file... -D_POSIX_PTHREAD_SEMANTICS [ library... ] int getgrnam_r(const char *name, struct group *grp, char *buffer, size_t bufsize, struct group **result); |
| | int getgrgid_r(gid_t gid, struct group *grp, char *buffer, size_t bufsize, struct group **result); |
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These functions are used to obtain entries describing user groups. Entries can come from any of the sources for group specified in the /etc/nsswitch.conf file
(see nsswitch.conf(4)).
The getgrnam() function searches the group database for an entry with the group name specified by the character string parameter name.
The getgrgid() function searches the group database for an entry with the (numeric) group id specified by gid.
The setgrent(), getgrent(), and endgrent() functions are used to enumerate group entries from the database.
The setgrent() function effectively rewinds the group database to allow repeated searches. It sets (or resets) the enumeration to the beginning of the set of group entries. This
function should be called before the first call to getgrent().
The getgrent() function returns a pointer to a structure containing the broken-out fields of an entry in the group database. When first called, getgrent() returns
a pointer to a group structure containing the next group structure in the group database. Successive calls may be used to search the entire database.
The endgrent() function may be called to close the group database and deallocate resources when processing is complete. It is permissible, though possibly less efficient, for the
process to call more group functions after calling endgrent().
The fgetgrent() function, unlike the other functions above, does not use nsswitch.conf. It reads and parses the next line from the stream f,
which is assumed to have the format of the group file (see group(4)).
Reentrant Interfaces
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The getgrnam(), getgrgid(), getgrent(), and fgetgrent() functions use static storage that is reused in each call, making
them unsafe for multithreaded applications.
The parallel functions getgrnam_r(), getgrgid_r(), getgrent_r(), and fgetgrent_r() provide reentrant interfaces for these
operations.
Each reentrant interface performs the same operation as its non-reentrant counterpart, named by removing the _r suffix. The reentrant interfaces, however, use buffers supplied
by the caller to store returned results, and are safe for use in both single-threaded and multithreaded applications.
Each reentrant interface takes the same arguments as its non-reentrant counterpart, as well as the following additional parameters. The grp argument must be a pointer to a struct group structure allocated by the caller. On successful completion, the function returns the group entry in this structure. Storage referenced by the group structure is allocated from the
memory provided with the buffer argument, which is bufsize characters in size. The maximum size needed for this buffer can be determined with the _SC_GETGR_R_SIZE_MAX sysconf(3C) parameter. The POSIX versions place a pointer
to the modified grp structure in the result parameter, instead of returning a pointer to this structure.
For enumeration in multithreaded applications, the position within the enumeration is a process-wide property shared by all threads. setgrent() may be used in a multithreaded application
but resets the enumeration position for all threads. If multiple threads interleave calls to getgrent_r(), the threads will enumerate disjoint subsets of the group database. Like their
non-reentrant counterparts, getgrnam_r() and getgrgid_r() leave the enumeration position in an indeterminate state.
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Group entries are represented by the struct group structure defined in <grp.h>:
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struct group {
char *gr_name; /* the name of the group */
char *gr_passwd; /* the encrypted group password */
gid_t gr_gid; /* the numerical group ID */
char **gr_mem; /* vector of pointers to member names */
};
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The getgrnam(), getgrnam_r(), getgrgid(), and getgrgid_r() functions each return a pointer to a struct group
if they successfully locate the requested entry; otherwise they return NULL. The POSIX functions getgrnam_r() and getgrgid_r() return 0 upon success or the error number in case of failure.
The getgrent(), getgrent_r(), fgetgrent(), and fgetgrent_r() functions each return a pointer to a struct group if they successfully enumerate an entry; otherwise they return NULL, indicating the end of the enumeration.
The getgrnam(), getgrgid(), getgrent(), and fgetgrent() functions use static storage, so returned data must be copied before
a subsequent call to any of these functions if the data is to be saved.
When the pointer returned by the reentrant functions getgrnam_r(), getgrgid_r(), getgrent_r(), and fgetgrent_r() is non-null,
it is always equal to the grp pointer that was supplied by the caller.
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The getgrnam(), getgrgid(), getgrent(), fgetgrent(), and fgetgrent_r() functions may fail
if:
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EINTR
- A signal was caught during the operation.
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EIO
- An I/O error has occurred.
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EMFILE
- There are OPEN_MAX file descriptors currently open in the calling process.
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ENFILE
- The maximum allowable number of files is currently open in the system.
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ERANGE
- The group file contains a line that exceeds 512 bytes.
The getgrnam_r(), getgrgid_r(), and getgrent_r() functions may fail if:
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ERANGE
- Insufficient storage was supplied by buffer and bufsize
to contain the data to be referenced by the resulting group structure.
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See attributes(5) for descriptions of the following
attributes:
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| MT-Level | See "Reentrant Interfaces" in DESCRIPTION. |
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When compiling multithreaded programs, see Intro(3), Notes On Multithreaded
Applications.
Programs that use the interfaces described in this manual page cannot be linked statically since the implementations of these functions employ dynamic loading and linking of shared objects at run
time.
Use of the enumeration interfaces getgrent() and getgrent_r() is discouraged; enumeration is supported for the group file, NIS,
and NIS+, but in general is not efficient and may not be supported for all database sources. The semantics of enumeration are discussed further in nsswitch.conf(4).
Previous releases allowed the use of ``+'' and ``-'' entries in /etc/group to selectively include and exclude entries from NIS. The primary usage
of these entries is superseded by the name service switch, so the ``+/-'' form may not be supported in future releases.
If required, the ``+/-'' functionality can still be obtained for NIS by specifying compat as the source for group.
If the ``+/-'' functionality is required in conjunction with NIS+, specify both compat as the source for group and nisplus as the source for the pseudo-database group_compat. See group(4), and nsswitch.conf(4)
for details.
Solaris 2.4 and earlier releases provided definitions of the getgrnam_r() and getgrgid_r() functions as specified in POSIX.1c Draft 6. The final POSIX.1c standard
changed the interface for these functions. Support for the Draft 6 interface is provided for compatibility only and may not be supported in future releases. New applications and libraries should use the
POSIX standard interface.
For POSIX.1c-compliant applications, the _POSIX_PTHREAD_SEMANTICS and _REENTRANT flags are automatically turned
on by defining the _POSIX_C_SOURCE flag with a value >= 199506L.
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