GETPWNAM(3) Linux Programmer's Manual GETPWNAM(3)
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);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
getpwnam_r(), getpwuid_r():
_POSIX_C_SOURCE
|| /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_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 user-
name 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 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; /* user information */
char *pw_dir; /* home directory */
char *pw_shell; /* shell program */
};
See passwd(5) for more information about these fields.
The getpwnam_r() and getpwuid_r() functions obtain the same information
as getpwnam() and getpwuid(), but store the retrieved passwd structure
in the space pointed to by pwd. The string fields pointed to by the
members of the passwd structure 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 call
sysconf(_SC_GETPW_R_SIZE_MAX)
returns either -1, without changing errno, or an initial suggested size
for buf. (If this size is too small, the call fails with ERANGE, in
which case the caller can retry with a larger buffer.)
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; see signal(7).
EIO I/O error.
EMFILE The per-process limit on the number of open file descriptors has
been reached.
ENFILE The system-wide limit on the total number of open files has been
reached.
ENOMEM Insufficient memory to allocate passwd structure.
ERANGE Insufficient buffer space supplied.
FILES
/etc/passwd
local password database file
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
+--------------+---------------+-----------------------------+
|Interface | Attribute | Value |
+--------------+---------------+-----------------------------+
|getpwnam() | Thread safety | MT-Unsafe race:pwnam locale |
+--------------+---------------+-----------------------------+
|getpwuid() | Thread safety | MT-Unsafe race:pwuid locale |
+--------------+---------------+-----------------------------+
|getpwnam_r(), | Thread safety | MT-Safe locale |
|getpwuid_r() | | |
+--------------+---------------+-----------------------------+
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. The pw_gecos field is not
specified in POSIX, but is present on most implementations.
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 var-
ious 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 argu-
ment.
#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), getsp-
nam(3), putpwent(3), setpwent(3), passwd(5)
COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2017-09-15 GETPWNAM(3)
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