1NEWGRP(1P) POSIX Programmer's Manual NEWGRP(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 newgrp - change to a new group
13
15 newgrp [-l][group]
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18 The newgrp utility shall create a new shell execution environment with
19 a new real and effective group identification. Of the attributes listed
20 in Shell Execution Environment, the new shell execution environment
21 shall retain the working directory, file creation mask, and exported
22 variables from the previous environment (that is, open files, traps,
23 unexported variables, alias definitions, shell functions, and set
24 options may be lost). All other aspects of the process environment that
25 are preserved by the exec family of functions defined in the System
26 Interfaces volume of IEEE Std 1003.1-2001 shall also be preserved by
27 newgrp; whether other aspects are preserved is unspecified.
28 A failure to assign the new group identifications (for example, for
30 security or password-related reasons) shall not prevent the new shell
31 execution environment from being created.
32 The newgrp utility shall affect the supplemental groups for the process
34 as follows:
35 * On systems where the effective group ID is normally in the supple‐
37 mentary group list (or whenever the old effective group ID actually
38 is in the supplementary group list):
39 * If the new effective group ID is also in the supplementary group
41 list, newgrp shall change the effective group ID.
42 * If the new effective group ID is not in the supplementary group
44 list, newgrp shall add the new effective group ID to the list, if
45 there is room to add it.
46 * On systems where the effective group ID is not normally in the sup‐
48 plementary group list (or whenever the old effective group ID is not
49 in the supplementary group list):
50 * If the new effective group ID is in the supplementary group list,
52 newgrp shall delete it.
53 * If the old effective group ID is not in the supplementary list,
55 newgrp shall add it if there is room.
56 Note: The System Interfaces volume of IEEE Std 1003.1-2001 does not
58 specify whether the effective group ID of a process is included
59 in its supplementary group list.
60 With no operands, newgrp shall change the effective group back to the
63 groups identified in the user's user entry, and shall set the list of
64 supplementary groups to that set in the user's group database entries.
65 If a password is required for the specified group, and the user is not
67 listed as a member of that group in the group database, the user shall
68 be prompted to enter the correct password for that group. If the user
69 is listed as a member of that group, no password shall be requested. If
70 no password is required for the specified group, it is implementation-
71 defined whether users not listed as members of that group can change to
72 that group. Whether or not a password is required, implementation-
73 defined system accounting or security mechanisms may impose additional
74 authorization restrictions that may cause newgrp to write a diagnostic
75 message and suppress the changing of the group identification.
76
78 The newgrp utility shall conform to the Base Definitions volume of
79 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
80 The following option shall be supported:
82 -l (The letter ell.) Change the environment to what would be
84 expected if the user actually logged in again.
85
88 The following operand shall be supported:
89 group A group name from the group database or a non-negative numeric
91 group ID. Specifies the group ID to which the real and effective
92 group IDs shall be set. If group is a non-negative numeric
93 string and exists in the group database as a group name (see
94 getgrnam()), the numeric group ID associated with that group
95 name shall be used as the group ID.
96
99 Not used.
100
102 The file /dev/tty shall be used to read a single line of text for pass‐
103 word checking, when one is required.
104
106 The following environment variables shall affect the execution of new‐
107 grp:
108 LANG Provide a default value for the internationalization variables
110 that are unset or null. (See the Base Definitions volume of
111 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
112 ables for the precedence of internationalization variables used
113 to determine the values of locale categories.)
114 LC_ALL If set to a non-empty string value, override the values of all
116 the other internationalization variables.
117 LC_CTYPE
119 Determine the locale for the interpretation of sequences of
120 bytes of text data as characters (for example, single-byte as
121 opposed to multi-byte characters in arguments).
122 LC_MESSAGES
124 Determine the locale that should be used to affect the format
125 and contents of diagnostic messages written to standard error.
126 NLSPATH
128 Determine the location of message catalogs for the processing of
129 LC_MESSAGES .
130
133 Default.
134
136 Not used.
137
139 The standard error shall be used for diagnostic messages and a prompt
140 string for a password, if one is required. Diagnostic messages may be
141 written in cases where the exit status is not available. See the EXIT
142 STATUS section.
143
145 None.
146
148 None.
149
151 If newgrp succeeds in creating a new shell execution environment,
152 whether or not the group identification was changed successfully, the
153 exit status shall be the exit status of the shell. Otherwise, the fol‐
154 lowing exit value shall be returned:
155 >0 An error occurred.
157
160 The invoking shell may terminate.
161 The following sections are informative.
163
165 There is no convenient way to enter a password into the group database.
166 Use of group passwords is not encouraged, because by their very nature
167 they encourage poor security practices. Group passwords may disappear
168 in the future.
169 A common implementation of newgrp is that the current shell uses exec
171 to overlay itself with newgrp, which in turn overlays itself with a new
172 shell after changing group. On some implementations, however, this may
173 not occur and newgrp may be invoked as a subprocess.
174 The newgrp command is intended only for use from an interactive termi‐
176 nal. It does not offer a useful interface for the support of applica‐
177 tions.
178 The exit status of newgrp is generally inapplicable. If newgrp is used
180 in a script, in most cases it successfully invokes a new shell and the
181 rest of the original shell script is bypassed when the new shell exits.
182 Used interactively, newgrp displays diagnostic messages to indicate
183 problems. But usage such as:
184 newgrp foo
187 echo $?
188 is not useful because the new shell might not have access to any status
190 newgrp may have generated (and most historical systems do not provide
191 this status). A zero status echoed here does not necessarily indicate
192 that the user has changed to the new group successfully. Following new‐
193 grp with the id command provides a portable means of determining
194 whether the group change was successful or not.
195
197 None.
198
200 Most historical implementations use one of the exec functions to imple‐
201 ment the behavior of newgrp. Errors detected before the exec leave the
202 environment unchanged, while errors detected after the exec leave the
203 user in a changed environment. While it would be useful to have newgrp
204 issue a diagnostic message to tell the user that the environment
205 changed, it would be inappropriate to require this change to some his‐
206 torical implementations.
207 The password mechanism is allowed in the group database, but how this
209 would be implemented is not specified.
210 The newgrp utility was retained in this volume of IEEE Std 1003.1-2001,
212 even given the existence of the multiple group permissions feature in
213 the System Interfaces volume of IEEE Std 1003.1-2001, for several rea‐
214 sons. First, in some implementations, the group ownership of a newly
215 created file is determined by the group of the directory in which the
216 file is created, as allowed by the System Interfaces volume of
217 IEEE Std 1003.1-2001; on other implementations, the group ownership of
218 a newly created file is determined by the effective group ID. On imple‐
219 mentations of the latter type, newgrp allows files to be created with a
220 specific group ownership. Finally, many implementations use the real
221 group ID in accounting, and on such systems, newgrp allows the account‐
222 ing identity of the user to be changed.
223
225 None.
226
228 Shell Command Language, sh, the System Interfaces volume of
229 IEEE Std 1003.1-2001, exec, getgrnam()
230
232 Portions of this text are reprinted and reproduced in electronic form
233 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
234 -- Portable Operating System Interface (POSIX), The Open Group Base
235 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
236 Electrical and Electronics Engineers, Inc and The Open Group. In the
237 event of any discrepancy between this version and the original IEEE and
238 The Open Group Standard, the original IEEE and The Open Group Standard
239 is the referee document. The original Standard can be obtained online
240 at http://www.opengroup.org/unix/online.html .
241IEEE/The Open Group 2003 NEWGRP(1P)