getpwnam

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
       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.)

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
       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.

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
       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);
       }

SEE ALSO
       endpwent(3), fgetpwent(3), getgrnam(3), getpw(3), getpwent(3),
       getspnam(3), putpwent(3), setpwent(3), passwd(5)

COLOPHON
       This page is part of release 5.02 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                               2019-03-06                       GETPWNAM(3)