PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       newgrp — change to a new group

SYNOPSIS         top

       newgrp [−l] [group]

DESCRIPTION         top

       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.1‐2008
       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.1‐2008 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
       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         top

       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         top

       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         top

       Not used.

INPUT FILES         top

       The file /dev/tty shall be used to read a single line of text for
       password checking, when one is required.

ENVIRONMENT VARIABLES         top

       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.1‐2008, 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         top

       Default.

STDOUT         top

       Not used.

STDERR         top

       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         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       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         top

       The invoking shell may terminate.

       The following sections are informative.

APPLICATION USAGE         top

       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         top

       None.

RATIONALE         top

       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.1‐2008, 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 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         top

       None.

SEE ALSO         top

       Chapter 2, Shell Command Language, sh(1p)

       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(1p), getgrnam(3p)

COPYRIGHT         top

       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 Electrical 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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                          NEWGRP(1P)