The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.
A newer edition of this document exists here


getgrgid, getgrgid_r - get group database entry for a group ID


#include <grp.h>

struct group *getgrgid(gid_t

[TSF] [Option Start] int getgrgid_r(gid_t gid, struct group *grp, char *buffer,
bufsize, struct group **result); [Option End]


The getgrgid() function shall search the group database for an entry with a matching gid.

The getgrgid() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.

[TSF] [Option Start] The getgrgid_r() function shall update the group structure pointed to by grp and store a pointer to that structure at the location pointed to by result. The structure shall contain an entry from the group database with a matching gid. Storage referenced by the group structure is allocated from the memory provided with the buffer parameter, which is bufsize bytes in size. The maximum size needed for this buffer can be determined with the {_SC_GETGR_R_SIZE_MAX} sysconf() parameter. A NULL pointer shall be returned at the location pointed to by result on error or if the requested entry is not found. [Option End]


Upon successful completion, getgrgid() shall return a pointer to a struct group with the structure defined in <grp.h> with a matching entry if one is found. The getgrgid() function shall return a null pointer if either the requested entry was not found, or an error occurred. On error, errno shall be set to indicate the error.

The return value may point to a static area which is overwritten by a subsequent call to getgrent(), getgrgid(), or getgrnam().

[TSF] [Option Start] If successful, the getgrgid_r() function shall return zero; otherwise, an error number shall be returned to indicate the error. [Option End]


The getgrgid() and getgrgid_r() functions may fail if:

An I/O error has occurred.
A signal was caught during getgrgid().
{OPEN_MAX} file descriptors are currently open in the calling process.
The maximum allowable number of files is currently open in the system.

[TSF] [Option Start] The getgrgid_r() function may fail if: [Option End]

[TSF] [Option Start] Insufficient storage was supplied via buffer and bufsize to contain the data to be referenced by the resulting group structure. [Option End]

The following sections are informative.


Finding an Entry in the Group Database

The following example uses getgrgid() to search the group database for a group ID that was previously stored in a stat structure, then prints out the group name if it is found. If the group is not found, the program prints the numeric value of the group for the entry.

#include <sys/types.h>
#include <grp.h>
#include <stdio.h>
struct stat statbuf;
struct group *grp;
if ((grp = getgrgid(statbuf.st_gid)) != NULL)
    printf(" %-8.8s", grp->gr_name);
    printf(" %-8d", statbuf.st_gid);


Applications wishing to check for error situations should set errno to 0 before calling getgrgid(). If errno is set on return, an error occurred.

The getgrgid_r() function is thread-safe and shall return values in a user-supplied buffer instead of possibly using a static data area that may be overwritten by each call.






endgrent(), getgrnam(), the Base Definitions volume of IEEE Std 1003.1-2001, <grp.h>, <limits.h>, <sys/types.h>


First released in Issue 1. Derived from System V Release 2.0.

Issue 5

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

The getgrgid_r() function is included for alignment with the POSIX Threads Extension.

A note indicating that the getgrgid() function need not be reentrant is added to the DESCRIPTION.

Issue 6

The getgrgid_r() function is marked as part of the Thread-Safe Functions option.

The Open Group Corrigendum U028/3 is applied, correcting text in the DESCRIPTION describing matching the gid.

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

In the SYNOPSIS, the optional include of the <sys/types.h> header is removed.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

The APPLICATION USAGE section is updated to include a note on the thread-safe function and its avoidance of possibly using a static data area.

IEEE PASC Interpretation 1003.1 #116 is applied, changing the description of the size of the buffer from bufsize characters to bytes.

End of informative text.

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