getgrgid_r (3p) - Linux Manuals

getgrgid_r: get group database entry for a group ID

PROLOG

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.

NAME

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

SYNOPSIS

#include <grp.h>

struct group *getgrgid(gid_t gid);

int getgrgid_r(gid_t gid, struct group *grp, char *buffer,
       size_t bufsize, struct group **result);

DESCRIPTION

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.

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.

RETURN VALUE

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().

If successful, the getgrgid_r() function shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

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

EIO

An I/O error has occurred.

EINTR

A signal was caught during getgrgid().

EMFILE

{OPEN_MAX} file descriptors are currently open in the calling process.

ENFILE

The maximum allowable number of files is currently open in the system.

The getgrgid_r() function may fail if:

ERANGE

Insufficient storage was supplied via buffer and bufsize to contain the data to be referenced by the resulting group structure.

The following sections are informative.

EXAMPLES

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);
else
    printf(" %-8d", statbuf.st_gid);
...

APPLICATION USAGE

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.

RATIONALE

None.

FUTURE DIRECTIONS

None.

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 http://www.opengroup.org/unix/online.html .