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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  System  Interfaces  volume  of POSIX.1‐2017 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  POSIX.1‐2017  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
       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  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  POSIX.1‐2017,  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-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   POSIX.1‐2017,   Section   8.2,
                 Internationalization   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
                 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 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
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 POSIX.1‐2017, even given the existence
       of the multiple group permissions feature in the System Interfaces volume of POSIX.1‐2017,
       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.1‐2017; 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 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.

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 .