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 (), getpwuid_r () |
Thread safety |
MT-Safe locale |
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)