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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | FILES | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON |
GETPWNAM(3) Linux Programmer's Manual GETPWNAM(3)
getpwnam, getpwnam_r, getpwuid, getpwuid_r - get password file entry
#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
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 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.)
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.
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.
/etc/passwd
local password database file
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() │ │ │
└──────────────┴───────────────┴─────────────────────────────┘
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD. The pw_gecos field is not
specified in POSIX, but is present on most implementations.
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.
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);
}
endpwent(3), fgetpwent(3), getgrnam(3), getpw(3), getpwent(3),
getspnam(3), putpwent(3), setpwent(3), passwd(5)
This page is part of release 4.12 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 2016-03-15 GETPWNAM(3)
Pages that refer to this page: capsh(1), getent(1), git-daemon(1), gitweb(1), chown(2), fgetpwent(3), getgrent_r(3), getgrnam(3), getpw(3), getpwent(3), getpwent_r(3), getspnam(3), getutent(3), putpwent(3), passwd(5), passwd(5@@shadow-utils), nscd(8), sulogin(8)