Name

getpwnam, getpwnam_r, getpwuid, getpwuid_r — get password file entry

Synopsis

#include <sys/types.h>
#include <pwd.h>
struct passwd *getpwnam( const char *name);
 
struct passwd *getpwuid( uid_t uid);
 
int getpwnam_r( const char *name,
  struct passwd *pwd,
  char *buf,
  size_t buflen,
  struct passwd **result);
 
int getpwuid_r( uid_t uid,
  struct passwd *pwd,
  char *buf,
  size_t buflen,
  struct passwd **result);
 
[Note] Note
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getpwnam_r(), getpwuid_r():
_POSIX_C_SOURCE >= 1 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE || _POSIX_SOURCE

DESCRIPTION

The getpwnam() function returns a pointer to a structure containing the broken-out fields of the record in the password database (e.g., the local password file /etc/passwd, NIS, and LDAP) that matches the username name.

The getpwuid() function returns a pointer to a structure containing the broken-out fields of the record in the password database that matches the user ID uid.

The getpwnam_r() and getpwuid_r() functions obtain the same information, but store the retrieved passwd structure in the space pointed to by pwd. This passwd structure contains pointers to strings, and these strings are stored in the buffer buf of size buflen. A pointer to the result (in case of success) or NULL (in case no entry was found or an error occurred) is stored in *result.

The passwd structure is defined in <pwd.h> as follows:

struct passwd {
  char * pw_name;
/* username */
  char * pw_passwd;
/* user password */
  uid_t   pw_uid;
/* user ID */
  gid_t   pw_gid;
/* group ID */
  char * pw_gecos;
/* real name */
  char * pw_dir;
/* home directory */
  char * pw_shell;
/* shell program */
};

The maximum needed size for buf can be found using sysconf(3) with the argument _SC_GETPW_R_SIZE_MAX.

RETURN VALUE

The getpwnam() and getpwuid() functions return a pointer to a passwd structure, or NULL if the matching entry is not found or an error occurs. If an error occurs, errno is set appropriately. If one wants to check errno after the call, it should be set to zero before the call.

The return value may point to a static area, and may be overwritten by subsequent calls to getpwent(3), getpwnam(), or getpwuid(). (Do not pass the returned pointer to free(3).)

On success, getpwnam_r() and getpwuid_r() return zero, and set *result to pwd. If no matching password record was found, these functions return 0 and store NULL in *result. In case of error, an error number is returned, and NULL is stored in *result.

ERRORS

0 or ENOENT or ESRCH or EBADF or EPERM or ...

The given name or uid was not found.

EINTR

A signal was caught.

EIO

I/O error.

EMFILE

The maximum number (OPEN_MAX) of files was open already in the calling process.

ENFILE

The maximum number of files was open already in the system.

ENOMEM

Insufficient memory to allocate passwd structure.

ERANGE

Insufficient buffer space supplied.

FILES

/etc/passwd

local password database file

CONFORMING TO

SVr4, 4.3BSD, POSIX.1-2001.

NOTES

The formulation given above under "RETURN VALUE" is from POSIX.1-2001. It does not call "not found" an error, and hence does not specify what value errno might have in this situation. But that makes it impossible to recognize errors. One might argue that according to POSIX errno should be left unchanged if an entry is not found. Experiments on various Unix-like systems show that lots of different values occur in this situation: 0, ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM and probably others.

The pw_dir field contains the name of the initial working directory of the user. Login programs use the value of this field to initialize the HOME environment variable for the login shell. An application that wants to determine its user's home directory should inspect the value of HOME (rather than the value getpwuid(getuid())−>pw_dir) since this allows the user to modify their notion of "the home directory" during a login session. To determine the (initial) home directory of another user, it is necessary to use getpwnam("username")−>pw_dir or similar.

EXAMPLE

The program below demonstrates the use of getpwnam_r() to find the full username and user ID for the username supplied as a command-line argument.

#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>

int
main(int argc, char *argv[])
{
    struct passwd pwd;
    struct passwd *result;
    char *buf;
    size_t bufsize;
    int s;

    if (argc != 2) {
        fprintf(stderr, "Usage: %s username\n", argv[0]);
        exit(EXIT_FAILURE);
    }

    bufsize = sysconf(_SC_GETPW_R_SIZE_MAX);
    if (bufsize == −1)          /* Value was indeterminate */
        bufsize = 16384;        /* Should be more than enough */

    buf = malloc(bufsize);
    if (buf == NULL) {
        perror("malloc");
        exit(EXIT_FAILURE);
    }

    s = getpwnam_r(argv[1], &pwd, buf, bufsize, &result);
    if (result == NULL) {
        if (s == 0)
            printf("Not found\n");
        else {
            errno = s;
            perror("getpwnam_r");
        }
        exit(EXIT_FAILURE);
    }

    printf("Name: %s; UID: %ld\n", pwd.pw_gecos, (long) pwd.pw_uid);
    exit(EXIT_SUCCESS);
}

SEE ALSO

endpwent(3), fgetpwent(3), getgrnam(3), getpw(3), getpwent(3), getspnam(3), putpwent(3), setpwent(3), passwd(5)

COLOPHON

This page is part of release 3.24 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


  Copyright 1993 David Metcalfe (davidprism.demon.co.uk)
and Copyright 2008, Linux Foundation, written by Michael Kerrisk
    <mtk.manpagesgmail.com>

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Since the Linux kernel and libraries are constantly changing, this
manual page may be incorrect or out-of-date.  The author(s) assume no
responsibility for errors or omissions, or for damages resulting from
the use of the information contained herein.  The author(s) may not
have taken the same level of care in the production of this manual,
which is licensed free of charge, as they might when working
professionally.

Formatted or processed versions of this manual, if unaccompanied by
the source, must acknowledge the copyright and authors of this work.

References consulted:
    Linux libc source code
    Lewine's "POSIX Programmer's Guide" (O'Reilly & Associates, 1991)
    386BSD man pages

Modified 1993-07-24 by Rik Faith (faithcs.unc.edu)
Modified 1996-05-27 by Martin Schulze (joeylinux.de)
Modified 2003-11-15 by aeb
2008-11-07, mtk, Added an example program for getpwnam_r().