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Linux 2.6 - man page for newgrp (linux section 1posix)

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

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 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 System Interfaces volume of IEEE Std 1003.1-2001 shall also be
       preserved by newgrp; 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 supplementary 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 supplementary 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 IEEE Std 1003.1-2001 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 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 pass-
       word 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 implementation-
       defined whether users not listed as members of  that  group  can  change  to  that  group.
       Whether	or  not a password is required, implementation-defined system accounting or secu-
       rity mechanisms may impose additional authorization restrictions that may cause newgrp  to
       write a diagnostic message and suppress the changing of the group identification.

OPTIONS
       The  newgrp  utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001,
       Section 12.2, Utility Syntax Guidelines.

       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-negative  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 password checking, when
       one is required.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of newgrp:

       LANG   Provide a default value for the internationalization variables that  are	unset  or
	      null. (See the Base Definitions volume of IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization Variables 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 interna-
	      tionalization 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 argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic 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 pass-
       word, if one is required. Diagnostic messages may be written in cases where the exit  sta-
       tus 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 following 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 terminal. It does not
       offer a useful interface for the support of applications.

       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  mes-
       sages 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 success-
       fully. Following newgrp 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 implement 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 historical 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  IEEE Std 1003.1-2001,  even  given  the
       existence  of  the  multiple  group permissions feature in the System Interfaces volume of
       IEEE Std 1003.1-2001, for several reasons. First, in some implementations, the group  own-
       ership  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	IEEE Std 1003.1-2001;  on
       other  implementations,	the  group ownership of a newly created file is determined by the
       effective group ID. On implementations of the latter type, newgrp allows files to be  cre-
       ated  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
       Shell  Command Language , sh , the System Interfaces volume of IEEE Std 1003.1-2001, exec,
       getgrnam()

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					NEWGRP(P)


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