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.TH NEWGRP "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

newgrp

\(em change to a new group

.SH SYNOPSIS

.LP

.nf

newgrp \fB[\fR\(mil\fB] [\fIgroup\fB]\fR

.fi

.SH DESCRIPTION

The

.IR newgrp

utility shall create a new shell execution environment with a new real

and effective group identification. Of the attributes listed in

.IR "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

.IR set

options may be lost). All other aspects of the process environment

that are preserved by the

.IR exec

family of functions defined in the System Interfaces volume of POSIX.1\(hy2008 shall also be preserved by

.IR newgrp ;

whether other aspects are preserved is unspecified.

.P

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.

.P

The

.IR newgrp

utility shall affect the supplemental groups for the process as

follows:

.IP " *" 4

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):

.RS 4 

.IP -- 4

If the new effective group ID is also in the supplementary group list,

.IR newgrp

shall change the effective group ID.

.IP -- 4

If the new effective group ID is not in the supplementary group list,

.IR newgrp

shall add the new effective group ID to the list, if there is room to

add it.

.RE

.IP " *" 4

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):

.RS 4 

.IP -- 4

If the new effective group ID is in the supplementary group list,

.IR newgrp

shall delete it.

.IP -- 4

If the old effective group ID is not in the supplementary list,

.IR newgrp

shall add it if there is room.

.RE

.TP 10

.BR Note:

The System Interfaces volume of POSIX.1\(hy2008 does not specify whether the effective group ID of a process

is included in its supplementary group list.

.P

.P

With no operands,

.IR 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.

.P

If the first argument is

.BR '\(mi' ,

the results are unspecified.

.P

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

.IR newgrp

to write a diagnostic message and suppress the changing of the group

identification.

.SH OPTIONS

The

.IR newgrp

utility shall conform to the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 12.2" ", " "Utility Syntax Guidelines",

except for the unspecified usage of

.BR '\(mi' .

.P

The following option shall be supported:

.IP "\fB\(mil\fP" 10

(The letter ell.) Change the environment to what would be expected if

the user actually logged in again.

.SH OPERANDS

The following operand shall be supported:

.IP "\fIgroup\fR" 10

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

.IR group

is a non-negative numeric string and exists in the group database as a

group name (see

\fIgetgrnam\fR()),

the numeric group ID associated with that group name shall be used as

the group ID.

.SH STDIN

Not used.

.SH "INPUT FILES"

The file

.BR /dev/tty

shall be used to read a single line of text for password checking, when

one is required.

.SH "ENVIRONMENT VARIABLES"

The following environment variables shall affect the execution of

.IR newgrp :

.IP "\fILANG\fP" 10

Provide a default value for the internationalization variables that are

unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 8.2" ", " "Internationalization Variables"

for the precedence of internationalization variables used to determine

the values of locale categories.)

.IP "\fILC_ALL\fP" 10

If set to a non-empty string value, override the values of all the

other internationalization variables.

.IP "\fILC_CTYPE\fP" 10

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).

.IP "\fILC_MESSAGES\fP" 10

.br

Determine the locale that should be used to affect the format and

contents of diagnostic messages written to standard error.

.IP "\fINLSPATH\fP" 10

Determine the location of message catalogs for the processing of

.IR LC_MESSAGES .

.SH "ASYNCHRONOUS EVENTS"

Default.

.SH STDOUT

Not used.

.SH 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.

.SH "OUTPUT FILES"

None.

.SH "EXTENDED DESCRIPTION"

None.

.SH "EXIT STATUS"

If

.IR 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:

.IP >0 6

An error occurred.

.SH "CONSEQUENCES OF ERRORS"

The invoking shell may terminate.

.LP

.IR "The following sections are informative."

.SH "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.

.P

A common implementation of

.IR newgrp

is that the current shell uses

.IR exec

to overlay itself with

.IR newgrp ,

which in turn overlays itself with a new shell after changing group.

On some implementations, however, this may not occur and

.IR newgrp

may be invoked as a subprocess.

.P

The

.IR newgrp

command is intended only for use from an interactive terminal. It does

not offer a useful interface for the support of applications.

.P

The exit status of

.IR newgrp

is generally inapplicable. If

.IR 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,

.IR newgrp

displays diagnostic messages to indicate problems. But usage such as:

.sp

.RS 4

.nf

\fB

newgrp foo

echo $?

.fi \fR

.P

.RE

.P

is not useful because the new shell might not have access to any status

.IR 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

.IR newgrp

with the

.IR id

command provides a portable means of determining whether the group

change was successful or not.

.SH EXAMPLES

None.

.SH RATIONALE

Most historical implementations use one of the

.IR exec

functions to implement the behavior of

.IR newgrp .

Errors detected before the

.IR exec

leave the environment unchanged, while errors detected after the

.IR exec

leave the user in a changed environment. While it would be useful to

have

.IR 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.

.P

The password mechanism is allowed in the group database, but how this

would be implemented is not specified.

.P

The

.IR newgrp

utility was retained in this volume of POSIX.1\(hy2008, even given the existence of the multiple

group permissions feature in the System Interfaces volume of POSIX.1\(hy2008, 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\(hy2008; on other implementations, the group ownership

of a newly created file is determined by the effective group ID. On

implementations of the latter type,

.IR 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,

.IR newgrp

allows the accounting identity of the user to be changed.

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "Chapter 2" ", " "Shell Command Language",

.IR "\fIsh\fR\^"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables",

.IR "Section 12.2" ", " "Utility Syntax Guidelines"

.P

The System Interfaces volume of POSIX.1\(hy2008,

.IR "\fIexec\fR\^",

.IR "\fIgetgrnam\fR\^(\|)"

.SH COPYRIGHT

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 .