man-pages/man3/getpwnam.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\" and Copyright 2008, Linux Foundation, written by Michael Kerrisk
.\"     <mtk.manpages@gmail.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.\" manual page may be incorrect or out-of-date.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 (faith@cs.unc.edu)
.\" Modified 1996-05-27 by Martin Schulze (joey@linux.de)
.\" Modified 2003-11-15 by aeb
.\" 2008-11-07, mtk, Added an example program for getpwnam_r().
.\"
.TH GETPWNAM 3  2009-03-30 "GNU" "Linux Programmer's Manual"
.SH NAME
getpwnam, getpwnam_r, getpwuid, getpwuid_r \- get password file entry
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <pwd.h>
.sp
.BI "struct passwd *getpwnam(const char *" name );
.sp
.BI "struct passwd *getpwuid(uid_t " uid );
.sp
.BI "int getpwnam_r(const char *" name ", struct passwd *" pwd ,
.br
.BI "            char *" buf ", size_t " buflen ", struct passwd **" result );
.sp
.BI "int getpwuid_r(uid_t " uid ", struct passwd *" pwd ,
.br
.BI "            char *" buf ", size_t " buflen ", struct passwd **" result );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.BR getpwnam_r (),
.BR getpwuid_r ():
.RS 4
_POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
_SVID_SOURCE || _POSIX_SOURCE
.RE
.ad b
.SH DESCRIPTION
The
.BR 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
.IR /etc/passwd ,
NIS, and LDAP)
that matches the username
.IR name .
.PP
The
.BR 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
.IR uid .
.PP
The
.BR getpwnam_r ()
and
.BR getpwuid_r ()
functions obtain the same information, but store the retrieved
.I passwd
structure in the space pointed to by
.IR pwd .
This
.I passwd
structure contains pointers to strings, and these strings
are stored in the buffer
.I buf
of size
.IR 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
.IR *result .
.PP
The \fIpasswd\fP structure is defined in \fI<pwd.h>\fP as follows:
.sp
.in +4n
.nf
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 */
};
.fi
.in
.PP
The maximum needed size for
.I buf
can be found using
.BR sysconf (3)
with the argument
.BR _SC_GETPW_R_SIZE_MAX .
.SH "RETURN VALUE"
The
.BR getpwnam ()
and
.BR getpwuid ()
functions return a pointer to a
.I passwd
structure, or NULL if the matching entry is not found or
an error occurs.
If an error occurs,
.I errno
is set appropriately.
If one wants to check
.I errno
after the call, it should be set to zero before the call.
.LP
The return value may point to a static area, and may be overwritten
by subsequent calls to
.BR getpwent (3),
.BR getpwnam (),
or
.BR getpwuid ().
(Do not pass the returned pointer to
.BR free (3).)
.LP
On success,
.BR getpwnam_r ()
and
.BR getpwuid_r ()
return zero, and set
.IR *result
to
.IR pwd .
If no matching password record was found,
these functions return 0 and store NULL in
.IR *result .
In case of error, an error number is returned, and NULL is stored in
.IR *result .
.SH ERRORS
.TP
.BR 0 " or " ENOENT " or " ESRCH " or " EBADF " or " EPERM " or ... "
The given
.I name
or
.I uid
was not found.
.TP
.B EINTR
A signal was caught.
.TP
.B EIO
I/O error.
.TP
.B EMFILE
The maximum number
.RB ( OPEN_MAX )
of files was open already in the calling process.
.TP
.B ENFILE
The maximum number of files was open already in the system.
.TP
.B ENOMEM
.\" not in POSIX
Insufficient memory to allocate
.I passwd
structure.
.\" This structure is static, allocated 0 or 1 times. No memory leak. (libc45)
.TP
.B ERANGE
Insufficient buffer space supplied.
.SH FILES
.TP
.I /etc/passwd
local password database file
.SH "CONFORMING TO"
SVr4, 4.3BSD, POSIX.1-2001.
.SH 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
.I errno
might have in this situation.
But that makes it impossible to recognize
errors.
One might argue that according to POSIX
.I 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.
.\" more precisely:
.\" AIX 5.1 - gives ESRCH
.\" OSF1 4.0g - gives EWOULDBLOCK
.\" libc, glibc up to version 2.6, Irix 6.5 - give ENOENT
.\" glibc since version 2.7 - give 0
.\" FreeBSD 4.8, OpenBSD 3.2, NetBSD 1.6 - give EPERM
.\" SunOS 5.8 - gives EBADF
.\" Tru64 5.1b, HP-UX-11i, SunOS 5.7 - give 0

The
.I 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
.B HOME
environment variable for the login shell.
An application that wants to determine its user's home directory
should inspect the value of
.B HOME
(rather than the value
.IR 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
.I getpwnam("username")\->pw_dir
or similar.
.SH EXAMPLE
The program below demonstrates the use of
.BR getpwnam_r ()
to find the full username and user ID for the username
supplied as a command-line argument.

.nf
#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);
}
.fi
.SH "SEE ALSO"
.BR endpwent (3),
.BR fgetpwent (3),
.BR getgrnam (3),
.BR getpw (3),
.BR getpwent (3),
.BR getspnam (3),
.BR putpwent (3),
.BR setpwent (3),
.BR passwd (5)