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 (con-
       sult 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 Shell Execution Environment, the new shell execution environment shall retain the working direc-
       tory,  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  pre-
       vent 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 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  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 security mechanisms may impose  additional  authorization  restric-
       tions 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, Internationalization Variables for the precedence  of  international-
              ization 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 stan-
              dard 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. Diagnos-
       tic 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 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 over-
       lays 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 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 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 imple-
       mentations, 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 IEEE Std 1003.1-2001; on other implementations, the group owner-
       ship of a newly created file is determined 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
       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, Copy-
       right (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   original   Standard   can   be   obtained   online   at   http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                    NEWGRP(1P)