Section: POSIX Programmer's Manual (3P)
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
--- group database entry functions
struct group *getgrent(void);
function shall return a pointer to a structure containing the broken-out
fields of an entry in the group database. If the group database
is not already open,
shall open it and return a pointer to a
structure containing the first entry in the database. Thereafter,
it shall return a pointer to a
structure containing the next
structure in the group database, so successive calls may be used
to search the entire database.
An implementation that provides extended security controls may impose
further implementation-defined restrictions on accessing the group
database. In particular, the system may deny the existence of some or
all of the group database entries associated with groups other than
those groups associated with the caller and may omit users other than
the caller from the list of members of groups in database entries that
function shall rewind the group database so that the next
call returns the first entry, allowing repeated searches.
function shall close the group database.
functions shall not change the setting of
On error, the
functions shall set
to indicate the error.
Since no value is returned by the
functions, an application wishing to check for error situations
to 0, then call the function, then check
These functions need not be thread-safe.
On successful completion,
shall return a pointer to a
structure. On end-of-file,
shall return a null pointer and shall not change the setting of
shall return a null pointer and
shall be set to indicate the error.
The application shall not modify the structure to which the return
value points, nor any storage areas pointed to by pointers within the
structure. The returned pointer, and pointers within the structure,
might be invalidated or the structure or the storage areas might be
overwritten by a subsequent call to
The returned pointer, and pointers within the structure, might
also be invalidated if the calling thread is terminated.
These functions may fail if:
A signal was caught during the operation.
An I/O error has occurred.
In addition, the
functions may fail if:
All file descriptors available to the process are currently open.
The maximum allowable number of files is currently open in the system.
The following sections are informative.
These functions are provided due to their historical usage.
Applications should avoid dependencies on fields in the group database,
whether the database is a single file, or where in the file system
name space the database resides. Applications should use
whenever possible because it avoids these dependencies.
The Base Definitions volume of POSIX.1-2017,
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
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