getpwuid

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 lo-
       cal 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  oc-
       curs.  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 re-
       turn 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.

NOTE
       The user password database mostly refers to /etc/passwd.  However, with
       recent systems it also refers to network wide databases using NIS, LDAP
       and other local files as configured in /etc/nsswitch.conf.

FILES
       /etc/passwd
              local password database file

       /etc/nsswitch.conf
              System Databases and Name Service Switch configuration file

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(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 var-
       ious 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  argu-
       ment.

       #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), getsp-
       nam(3), putpwent(3), setpwent(3), nsswitch.conf(5), passwd(5)

COLOPHON
       This page is part of release 5.05 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)