The Open Group Base Specifications Issue 7, 2018 edition
IEEE Std 1003.1-2017 (Revision of IEEE Std 1003.1-2008)
Copyright © 2001-2018 IEEE and The Open Group


endgrent, getgrent, setgrent - group database entry functions


[XSI] [Option Start] #include <grp.h>

void endgrent(void);
struct group *getgrent(void);
void setgrent(void); [Option End]


The getgrent() 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, getgrent() shall open it and return a pointer to a group structure containing the first entry in the database. Thereafter, it shall return a pointer to a group structure containing the next group 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 are returned.

The setgrent() function shall rewind the group database so that the next getgrent() call returns the first entry, allowing repeated searches.

The endgrent() function shall close the group database.

The setgrent() and endgrent() functions shall not change the setting of errno if successful.

On error, the setgrent() and endgrent() functions shall set errno to indicate the error.

Since no value is returned by the setgrent() and endgrent() functions, an application wishing to check for error situations should set errno to 0, then call the function, then check errno.

These functions need not be thread-safe.


On successful completion, getgrent() shall return a pointer to a group structure. On end-of-file, getgrent() shall return a null pointer and shall not change the setting of errno. On error, getgrent() shall return a null pointer and errno 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 getgrgid(), getgrnam(), or getgrent(). 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 getgrent() and setgrent() 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 getgrnam() and getgrgid() whenever possible because it avoids these dependencies.






endpwent, getgrgid, getgrnam, getlogin

XBD <grp.h>


First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

Normative text previously in the APPLICATION USAGE section is moved to the RETURN VALUE section.

A note indicating that these functions need not be reentrant is added to the DESCRIPTION.

Issue 6

In the DESCRIPTION, the note about reentrancy is expanded to cover thread-safety.

Issue 7

Austin Group Interpretation 1003.1-2001 #156 is applied.

SD5-XBD-ERN-4 is applied, changing the definition of the [EMFILE] error.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0080 [75] is applied.

POSIX.1-2008, Technical Corrigendum 2, XSH/TC2-2008/0086 [493], XSH/TC2-2008/0087 [656], and XSH/TC2-2008/0088 [493] are applied.

End of informative text.


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