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Linux 2.6 - man page for getpwnam_r (linux section 3)

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 >= 1 || _XOPEN_SOURCE || _BSD_SOURCE || _SVID_SOURCE || _POSIX_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 getpwnam_r() and getpwuid_r() functions obtain the same  information,  but  store  the
       retrieved passwd structure in the space pointed to by pwd.  This passwd structure contains
       pointers to strings, and these strings 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 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;      /* real name */
	       char   *pw_dir;	      /* home directory */
	       char   *pw_shell;      /* shell program */
	   };

       The maximum needed  size  for  buf  can	be  found  using  sysconf(3)  with  the  argument
       _SC_GETPW_R_SIZE_MAX.

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.

       EIO    I/O error.

       EMFILE The maximum number (OPEN_MAX) of files was open already in the calling process.

       ENFILE The maximum number of files was open already in the system.

       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

CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.

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 situ-
       ation.	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 getpw-
       nam("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), nsswitch.conf(5), passwd(5)

COLOPHON
       This page is part of release 3.27 of the Linux man-pages project.  A  description  of  the
       project,   and	information  about  reporting  bugs,  can  be  found  at  http://www.ker-
       nel.org/doc/man-pages/.

GNU					    2009-03-30				      GETPWNAM(3)


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