getgrnam(3C) Standard C Library Functions getgrnam(3C)NAME
getgrnam, getgrnam_r, getgrent, getgrent_r, getgrgid, getgrgid_r, set‐
grent, endgrent, fgetgrent, fgetgrent_r - group database entry func‐
tions
SYNOPSIS
#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);
void setgrent(void);
void endgrent(void);
struct group *fgetgrent(FILE *f);
struct group *fgetgrent_r(FILE *f, struct group *grp, char *buffer, int
bufsize);
Standard comforming
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 buf‐
size, struct group **result);
DESCRIPTION
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 enu‐
merate 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 can be
used to search the entire database.
The endgrent() function can 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
The getgrnam(), getgrgid(), getgrent(), and fgetgrent() functions use
thread-specific storage that is reused in each call to one of these
functions by the same thread, making them safe to use but not recom‐
mended 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-reen‐
trant counterpart, named by removing the _r suffix. The reentrant
interfaces, however, use buffers supplied by the caller to store
returned results instead of using thread-specific data that can be
overwritten by each call. They 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 allo‐
cated from the memory provided with the buffer argument that 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
standard-conforming versions place a pointer to the modified grp struc‐
ture in the result parameter, instead of returning a pointer to this
structure. A null pointer is returned at the location pointed to by
result on error or if the requested entry is not found.
For enumeration in multithreaded applications, the position within the
enumeration is a process-wide property shared by all threads. The set‐
grent() function can be used in a multithreaded application but resets
the enumeration position for all threads. If multiple threads inter‐
leave calls to getgrent_r(), the threads will enumerate disjoint sub‐
sets of the group database. Like their non-reentrant counterparts, get‐
grnam_r() and getgrgid_r() leave the enumeration position in an inde‐
terminate state.
group Structure
Group entries are represented by the struct group structure defined in
<grp.h>:
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 */
};
RETURN VALUES
The getgrnam(), getgrnam_r(), getgrgid(), and getgrgid_r() functions
each return a pointer to a struct group if they successfully locate the
requested entry. They return a null pointer if either the requested
entry was not found or an error occurred. On error, errno is set to
indicate the error. The standard-conforming functions getgrnam_r() and
getgrgid_r() return 0 upon success or an error number in case of fail‐
ure.
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 a null pointer on end-of-file or error.
On error, errno is set to indicate the error.
The getgrnam(), getgrgid(), getgrent(), and fgetgrent() functions use
thread-specific data storage, so returned data must be copied before a
subsequent call to any of these functions if the data are to be saved.
When the pointer returned by the reentrant functions getgrnam_r(), get‐
grgid_r(), getgrent_r(), and fgetgrent_r() is non-null, it is always
equal to the grp pointer that was supplied by the caller.
Applications wishing to check for error situations should set errno to
0 before calling getgrnam(), getgrnam_r(), getgrent(), getgrent_r()get‐
grgid(), getgrgid_r(), fgetgrent(), and fgetgrent_r(). If these func‐
tions return a null pointer and errno is non-zero, an error occurred.
ERRORS
The getgrent_r(), fgetgrent(), and fgetgrent_r() functions will fail
if:
EIO An I/O error has occurred.
ERANGE Insufficient storage was supplied by buffer and bufsize
to contain the data to be referenced by the resulting
group structure.
The getgrent_r() function will fail if:
EMFILE There are {OPEN_MAX} file descriptors currently open in
the calling process.
ENFILE The maximum allowable number of files is currently open
in the system.
The getgrnam(), getgrnam_r(), getgrgid(), getgrgid_r(), and getgrent()
functions may fail if:
EINTR A signal was caught during the operation.
EIO An I/O error has occurred.
EMFILE There are {OPEN_MAX} file descriptors currently open in
the calling process.
ENFILE The maximum allowable number of files is currently open
in the system.
The getgrnam_r() and getgrgid_r() functions may fail if:
ERANGE Insufficient storage was supplied by buffer and bufsize
to contain the data to be referenced by the resulting
group structure.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │endgrent(), getgrent(), │
│ │getgrgid(), getgrgid_r(), │
│ │getgrnam(), getgrnam_r(), │
│ │and setgrent() are Stan‐ │
│ │dard. │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │See Reentrant Interfaces in │
│ │DESCRIPTION. │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOIntro(3), getpwnam(3C), group(4), nsswitch.conf(4), passwd(4),
attributes(5), standards(5)NOTES
When compiling multithreaded programs, see Intro(3).
Use of the enumeration interfaces getgrent() and getgrent_r() is dis‐
couraged; enumeration is supported for the group file, NIS, and NIS+,
but in general is not efficient and might 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 might 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 nss‐
witch.conf(4) for details.
Solaris 2.4 and earlier releases provided definitions of the getgr‐
nam_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 might not be supported in future releases. New applications and
libraries should use the standard-conforming interface.
For POSIX.1c-conforming applications, the _POSIX_PTHREAD_SEMANTICS and
_REENTRANT flags are automatically turned on by defining the
_POSIX_C_SOURCE flag with a value ≥199506L.
SunOS 5.10 5 Apr 2004 getgrnam(3C)
