| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | FILES | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON | The Linux Programming Interface |
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 >= 1 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE ||
_POSIX_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 maximum size needed for buf can be found using sysconf(3) with the
argument _SC_GETPW_R_SIZE_MAX.
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.
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.
/etc/passwd
local password database file
SVr4, 4.3BSD, POSIX.1-2001. 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 3.32 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/.
GNU 2010-10-21 GETPWNAM(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface