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

       endgrent, getgrent, setgrent — group database entry functions

SYNOPSIS

       #include <grp.h>

       void endgrent(void);
       struct group *getgrent(void);
       void setgrent(void);

DESCRIPTION

       The  getgrent()  function  shall return a pointer to a structure containing the broken-out
       fields of an entry in the group database. If the  group  database  is  not  already  open,
       getgrent()  shall  open  it and return a pointer to a group structure containing the first
       entry in the database. Thereafter,  it  shall  return  a  pointer  to  a  group  structure
       containing the next group structure in the group database, so successive calls may be used
       to search the entire database.

       An  implementation  that  provides  extended  security   controls   may   impose   further
       implementation-defined  restrictions  on  accessing the group database. In particular, the
       system may deny the existence of some or all of the group database entries associated with
       groups  other  than  those groups associated with the caller and may omit users other than
       the caller from the list of members of groups in database entries that are returned.

       The setgrent() function shall rewind the group database so that the next  getgrent()  call
       returns the first entry, allowing repeated searches.

       The endgrent() function shall close the group database.

       The  setgrent()  and  endgrent()  functions  shall  not  change  the  setting  of errno if
       successful.

       On error, the setgrent() and endgrent() functions shall set errno to indicate the error.

       Since no value is returned by the setgrent()  and  endgrent()  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, getgrent() shall return a pointer to a group structure. On  end-
       of-file, getgrent() shall return a null pointer and shall not change the setting of errno.
       On error, getgrent() 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 getgrgid(), getgrnam(), or  getgrent().   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, the getgrent() and setgrent() functions 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

       None.

APPLICATION USAGE

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

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       endpwent(), getgrgid(), getgrnam(), getlogin()

       The Base Definitions volume of POSIX.1‐2017, <grp.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 .