getpwnam(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | FILES | ATTRIBUTES | CONFORMING TO | NOTES | EXAMPLES | SEE ALSO | COLOPHON

GETPWNAM(3)             Linux Programmer's Manual            GETPWNAM(3)

NAME         top

       getpwnam, getpwnam_r, getpwuid, getpwuid_r - get password file
       entry

SYNOPSIS         top

       #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 *restrict buf, size_t buflen,
                      struct passwd **restrict result);
       int getpwuid_r(uid_t uid, struct passwd *restrict pwd,
                      char *restrict buf, 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

DESCRIPTION         top

       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         top

       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.

ERRORS         top

       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         top

       /etc/passwd
              local password database file

ATTRIBUTES         top

       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         top

       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         top

       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.

EXAMPLES         top

       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 <stdint.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: %jd\n", pwd.pw_gecos,
                   (intmax_t) pwd.pw_uid);
           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.13 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                            2021-03-22                    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)pmsetprocessidentity(3)putpwent(3)org.freedesktop.home1(5)passwd(5)passwd(5@@shadow-utils)system_data_types(7)nscd(8)sulogin(8)