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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | FILES | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
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getpwnam(3) Library Functions Manual getpwnam(3)
getpwnam, getpwnam_r, getpwuid, getpwuid_r - get password file
entry
Standard C library (libc, -lc)
#include <sys/types.h>
#include <pwd.h>
struct passwd *getpwnam(const char *name);
struct passwd *getpwuid(uid_t uid);
int getpwnam_r(const char *restrict name, struct passwd *restrict pwd,
char buf[restrict .buflen], size_t buflen,
struct passwd **restrict result);
int getpwuid_r(uid_t uid, struct passwd *restrict pwd,
char buf[restrict .buflen], size_t buflen,
struct passwd **restrict result);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getpwnam_r(), getpwuid_r():
_POSIX_C_SOURCE
|| /* glibc <= 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 to indicate
the error. 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() │ │ │
└───────────────┴───────────────┴───────────────────────────────┘
The pw_gecos field is not specified in POSIX, but is present on
most implementations.
POSIX.1-2008.
POSIX.1-2001, SVr4, 4.3BSD.
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 <errno.h>
#include <pwd.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
struct passwd pwd;
struct passwd *result;
char *buf;
long 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: %jd\n", pwd.pw_gecos,
(intmax_t) pwd.pw_uid);
exit(EXIT_SUCCESS);
}
endpwent(3), fgetpwent(3), getgrnam(3), getpw(3), getpwent(3),
getspnam(3), putpwent(3), setpwent(3), passwd(5)
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Linux man-pages 6.9.1 2024-06-15 getpwnam(3)
Pages that refer to this page: capsh(1), getent(1), git-daemon(1), gitweb(1), strace(1), chown(2), fgetpwent(3), getgrent_r(3), getgrnam(3), getpw(3), getpwent(3), getpwent_r(3), getspnam(3), getutent(3), id_t(3type), pmsetprocessidentity(3), putpwent(3), org.freedesktop.home1(5), passwd(5), passwd(5@@shadow-utils), nscd(8), sulogin(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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