Manual Page - newgrp(1p)
Manual Reference Pages - NEWGRP (P)
NAME
newgrp - change to a new group
CONTENTS
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
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:
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*
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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):
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*
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If the new effective group ID is also in the supplementary group list,
newgrp shall change the effective group ID.
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*
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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.
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*
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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):
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*
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If the new effective group ID is in the supplementary group list,
newgrp shall delete it.
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*
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If the old effective group ID is not in the supplementary list, newgrp
shall add it if there is room.
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Note:
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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.
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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
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:
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-l
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(The letter ell.) Change the environment to what would be expected
if the user actually logged in again.
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OPERANDS
The following operand shall be supported:
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group
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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.
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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:
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LANG
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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 internationalization variables used to determine
the values of locale categories.)
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LC_ALL
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If set to a non-empty string value, override the values of all the
other internationalization variables.
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LC_CTYPE
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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).
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LC_MESSAGES
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Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
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NLSPATH
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Determine the location of message catalogs for the processing of LC_MESSAGES
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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:
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 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 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
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.
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 original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
| IEEE/The Open Group | NEWGRP (P) | 2003 |
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