PROLOG

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

NAME

       endpwent, getpwent, setpwent — user database functions

SYNOPSIS

       #include <pwd.h>

       void endpwent(void);
       struct passwd *getpwent(void);
       void setpwent(void);

DESCRIPTION

       These functions shall retrieve information about users.

       The  getpwent()  function  shall  return  a pointer to a structure containing the broken-out fields of an
       entry in the user database. Each entry in the user database contains a  passwd  structure.  If  the  user
       database  is  not  already  open,  getpwent()  shall  open  it and return a pointer to a passwd structure
       containing the first entry in the database. Thereafter, it shall return a pointer to a  passwd  structure
       containing  the  next  entry in the user database. Successive calls can be used to search the entire user
       database.

       If an end-of-file or an error is encountered on reading, getpwent() shall return a null pointer.

       An implementation that provides extended security  controls  may  impose  further  implementation-defined
       restrictions  on accessing the user database. In particular, the system may deny the existence of some or
       all of the user database entries associated with users other than the caller.

       The setpwent() function shall rewind the user database so that the next getpwent() call returns the first
       entry, allowing repeated searches.

       The endpwent() function shall close the user database.

       The setpwent() and endpwent() functions shall not change the setting of errno if successful.

       On error, the setpwent() and endpwent() functions shall set errno to indicate the error.

       Since  no  value  is returned by the setpwent() and endpwent() functions, an application wishing to check
       for error situations should set errno to 0, then call the function, then check errno.

       These functions need not be thread-safe.

RETURN VALUE

       On successful completion, getpwent() shall return a  pointer  to  a  passwd  structure.  On  end-of-file,
       getpwent()  shall  return a null pointer and shall not change the setting of errno.  On error, getpwent()
       shall return a null pointer and errno shall be set to indicate the error.

       The application shall not modify the structure to which the return value points, nor  any  storage  areas
       pointed  to  by  pointers  within the structure. The returned pointer, and pointers within the structure,
       might be invalidated or the structure or the storage areas might be overwritten by a subsequent  call  to
       getpwuid(),  getpwnam(),  or  getpwent().  The returned pointer, and pointers within the structure, might
       also be invalidated if the calling thread is terminated.

ERRORS

       These functions may fail if:

       EINTR  A signal was caught during the operation.

       EIO    An I/O error has occurred.

       In addition, getpwent() and setpwent() may fail if:

       EMFILE All file descriptors available to the process are currently open.

       ENFILE The maximum allowable number of files is currently open in the system.

       The following sections are informative.

EXAMPLES

   Searching the User Database
       The following example uses the getpwent() function to  get  successive  entries  in  the  user  database,
       returning  a  pointer  to  a  passwd  structure  that  contains  information about each user. The call to
       endpwent() closes the user database and cleans up.

           #include <pwd.h>
           #include <stdio.h>

           void printname(uid_t uid)
           {
               struct passwd *pwd;

               setpwent();
               while((pwd = getpwent()) != NULL) {
                   if (pwd->pw_uid == uid) {
                       printf("name=%s\n",pwd->pw_name);
                       break;
                   }
               }
               endpwent();
           }

APPLICATION USAGE

       These functions are provided due to their historical usage.  Applications should  avoid  dependencies  on
       fields  in the password database, whether the database is a single file, or where in the file system name
       space the database resides. Applications should use getpwuid() whenever possible because it avoids  these
       dependencies.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       endgrent(), getlogin(), getpwnam(), getpwuid()

       The Base Definitions volume of POSIX.1‐2017, <pwd.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any discrepancy between this version and the original
       IEEE  and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document.
       The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have  been  introduced
       during   the   conversion  of  the  source  files  to  man  page  format.  To  report  such  errors,  see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .