GENWiki

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 user-
     name 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).

     allbox;  lb  lb  lb  l  l  l.   Interface Attribute Value T{ getpwnam()
     T}   Thread   safety MT-Unsafe   race:pwnam   locale   T{    getpwuid()
     T}   Thread safety  MT-Unsafe race:pwuid locale T{ getpwnam_r(),
     getpwuid_r() T}   Thread safety  MT-Safe locale

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); }