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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 |
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NEWGRP(1P) POSIX Programmer's Manual NEWGRP(1P)
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.
newgrp — change to a new group
newgrp [−l] [group]
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.
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.
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.
Not used.
The file /dev/tty shall be used to read a single line of text for
password checking, when one is required.
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.
Default.
Not used.
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.
None.
None.
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.
The invoking shell may terminate.
The following sections are informative.
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.
None.
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.
None.
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)
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)
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