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 .