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NEWGRP(1P)		   POSIX Programmer's Manual		    NEWGRP(1P)

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
       newgrp — change to a new group

SYNOPSIS
       newgrp [−l] [group]

DESCRIPTION
       The newgrp utility shall create a new shell execution environment  with
       a new real and effective group identification. Of the attributes listed
       in Section 2.12, Shell Execution Environment, the new  shell  execution
       environment shall retain the working directory, file creation mask, and
       exported variables from the previous environment (that is, open	files,
       traps,  unexported  variables,  alias definitions, shell functions, and
       set options may be lost). All other aspects of the process  environment
       that  are preserved by the exec family of functions defined in the Sys‐
       tem Interfaces volume of POSIX.1‐2008 shall also be preserved  by  new‐
       grp; whether other aspects are preserved is unspecified.

       A  failure  to  assign  the new group identifications (for example, for
       security or password-related reasons) shall not prevent the  new	 shell
       execution environment from being created.

       The newgrp utility shall affect the supplemental groups for the process
       as follows:

	*  On systems where the effective group ID is normally in the  supple‐
	   mentary group list (or whenever the old effective group ID actually
	   is in the supplementary group list):

	   --  If the new effective group ID  is  also	in  the	 supplementary
	       group list, newgrp shall change the effective group ID.

	   --  If the new effective group ID is not in the supplementary group
	       list, newgrp shall add the new effective group ID to the	 list,
	       if there is room to add it.

	*  On systems where the effective group ID is not normally in the sup‐
	   plementary group list (or whenever the old effective	 group	ID  is
	   not in the supplementary group list):

	   --  If  the	new  effective	group ID is in the supplementary group
	       list, newgrp shall delete it.

	   --  If the old effective group ID is not in the supplementary list,
	       newgrp shall add it if there is room.

       Note:	 The System Interfaces volume of POSIX.1‐2008 does not specify
		 whether the effective group ID of a process  is  included  in
		 its supplementary group list.

       With  no	 operands, newgrp shall change the effective group back to the
       groups identified in the user's user entry, and shall set the  list  of
       supplementary groups to that set in the user's group database entries.

       If the first argument is '−', the results are unspecified.

       If  a password is required for the specified group, and the user is not
       listed as a member of that group in the group database, the user	 shall
       be  prompted  to enter the correct password for that group. If the user
       is listed as a member of that group, no password	 shall	be  requested.
       If  no  password is required for the specified group, it is implementa‐
       tion-defined whether users not listed as	 members  of  that  group  can
       change  to that group. Whether or not a password is required, implemen‐
       tation-defined system accounting	 or  security  mechanisms  may	impose
       additional  authorization restrictions that may cause newgrp to write a
       diagnostic message and suppress the changing of the  group  identifica‐
       tion.

OPTIONS
       The  newgrp  utility  shall  conform  to the Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, except  for  the
       unspecified usage of '−'.

       The following option shall be supported:

       −l	 (The  letter  ell.)  Change  the environment to what would be
		 expected if the user actually logged in again.

OPERANDS
       The following operand shall be supported:

       group	 A group name  from  the  group	 database  or  a  non-negative
		 numeric  group	 ID.  Specifies the group ID to which the real
		 and effective group IDs shall be set. If group is a non-nega‐
		 tive  numeric	string	and  exists in the group database as a
		 group name (see getgrnam()), the numeric group ID  associated
		 with that group name shall be used as the group ID.

STDIN
       Not used.

INPUT FILES
       The file /dev/tty shall be used to read a single line of text for pass‐
       word checking, when one is required.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of  new‐
       grp:

       LANG	 Provide  a  default  value for the internationalization vari‐
		 ables that are unset or null. (See the Base Definitions  vol‐
		 ume  of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
		 ables for the precedence  of  internationalization  variables
		 used to determine the values of locale categories.)

       LC_ALL	 If  set  to  a non-empty string value, override the values of
		 all the other internationalization variables.

       LC_CTYPE	 Determine the locale for the interpretation of	 sequences  of
		 bytes of text data as characters (for example, single-byte as
		 opposed to multi-byte characters in arguments).

       LC_MESSAGES
		 Determine the locale that should be used to affect the format
		 and  contents	of  diagnostic	messages  written  to standard
		 error.

       NLSPATH	 Determine the location of message catalogs for the processing
		 of LC_MESSAGES.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       Not used.

STDERR
       The  standard  error shall be used for diagnostic messages and a prompt
       string for a password, if one is required. Diagnostic messages  may  be
       written	in  cases where the exit status is not available. See the EXIT
       STATUS section.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       If newgrp succeeds in  creating	a  new	shell  execution  environment,
       whether	or  not the group identification was changed successfully, the
       exit status shall be the exit status of the shell. Otherwise, the  fol‐
       lowing exit value shall be returned:

       >0    An error occurred.

CONSEQUENCES OF ERRORS
       The invoking shell may terminate.

       The following sections are informative.

APPLICATION USAGE
       There is no convenient way to enter a password into the group database.
       Use of group passwords is not encouraged, because by their very	nature
       they  encourage	poor security practices. Group passwords may disappear
       in the future.

       A common implementation of newgrp is that the current shell  uses  exec
       to overlay itself with newgrp, which in turn overlays itself with a new
       shell after changing group.  On some implementations, however, this may
       not occur and newgrp may be invoked as a subprocess.

       The  newgrp command is intended only for use from an interactive termi‐
       nal. It does not offer a useful interface for the support  of  applica‐
       tions.

       The  exit status of newgrp is generally inapplicable. If newgrp is used
       in a script, in most cases it successfully invokes a new shell and  the
       rest of the original shell script is bypassed when the new shell exits.
       Used interactively, newgrp displays  diagnostic	messages  to  indicate
       problems. But usage such as:

	   newgrp foo
	   echo $?

       is not useful because the new shell might not have access to any status
       newgrp may have generated (and most historical systems do  not  provide
       this  status).  A zero status echoed here does not necessarily indicate
       that the user has changed to the new group successfully. Following new‐
       grp  with  the  id  command  provides  a	 portable means of determining
       whether the group change was successful or not.

EXAMPLES
       None.

RATIONALE
       Most historical implementations use one of the exec functions to imple‐
       ment the behavior of newgrp.  Errors detected before the exec leave the
       environment unchanged, while errors detected after the exec  leave  the
       user  in a changed environment. While it would be useful to have newgrp
       issue a diagnostic message  to  tell  the  user	that  the  environment
       changed,	 it would be inappropriate to require this change to some his‐
       torical implementations.

       The password mechanism is allowed in the group database, but  how  this
       would be implemented is not specified.

       The  newgrp  utility  was retained in this volume of POSIX.1‐2008, even
       given the existence of the multiple group permissions  feature  in  the
       System  Interfaces  volume of POSIX.1‐2008, for several reasons. First,
       in some implementations, the group ownership of a newly created file is
       determined  by the group of the directory in which the file is created,
       as allowed by the System Interfaces volume of  POSIX.1‐2008;  on	 other
       implementations,	 the group ownership of a newly created file is deter‐
       mined by the effective group ID. On implementations of the latter type,
       newgrp  allows  files  to  be  created with a specific group ownership.
       Finally, many implementations use the real group ID in accounting,  and
       on  such	 systems, newgrp allows the accounting identity of the user to
       be changed.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Chapter 2, Shell Command Language, sh

       The Base Definitions volume of  POSIX.1‐2008,  Chapter  8,  Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, exec, getgrnam()

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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.unix.org/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.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			    NEWGRP(1P)
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