1ID(1P) POSIX Programmer's Manual ID(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 id — return user identity
13
15 id [user]
16 id -G [-n] [user]
18 id -g [-nr] [user]
20 id -u [-nr] [user]
22
24 If no user operand is provided, the id utility shall write the user and
25 group IDs and the corresponding user and group names of the invoking
26 process to standard output. If the effective and real IDs do not match,
27 both shall be written. If multiple groups are supported by the underly‐
28 ing system (see the description of {NGROUPS_MAX} in the System Inter‐
29 faces volume of POSIX.1‐2017), the supplementary group affiliations of
30 the invoking process shall also be written.
31 If a user operand is provided and the process has appropriate privi‐
33 leges, the user and group IDs of the selected user shall be written. In
34 this case, effective IDs shall be assumed to be identical to real IDs.
35 If the selected user has more than one allowable group membership
36 listed in the group database, these shall be written in the same manner
37 as the supplementary groups described in the preceding paragraph.
38
40 The id utility shall conform to the Base Definitions volume of
41 POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
42 The following options shall be supported:
44 -G Output all different group IDs (effective, real, and supple‐
46 mentary) only, using the format "%u\n". If there is more
47 than one distinct group affiliation, output each such affili‐
48 ation, using the format " %u", before the <newline> is out‐
49 put.
50 -g Output only the effective group ID, using the format "%u\n".
52 -n Output the name in the format "%s" instead of the numeric ID
54 using the format "%u".
55 -r Output the real ID instead of the effective ID.
57 -u Output only the effective user ID, using the format "%u\n".
59
61 The following operand shall be supported:
62 user The login name for which information is to be written.
64
66 Not used.
67
69 None.
70
72 The following environment variables shall affect the execution of id:
73 LANG Provide a default value for the internationalization vari‐
75 ables that are unset or null. (See the Base Definitions vol‐
76 ume of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
77 ables for the precedence of internationalization variables
78 used to determine the values of locale categories.)
79 LC_ALL If set to a non-empty string value, override the values of
81 all the other internationalization variables.
82 LC_CTYPE Determine the locale for the interpretation of sequences of
84 bytes of text data as characters (for example, single-byte as
85 opposed to multi-byte characters in arguments).
86 LC_MESSAGES
88 Determine the locale that should be used to affect the format
89 and contents of diagnostic messages written to standard error
90 and informative messages written to standard output.
91 NLSPATH Determine the location of message catalogs for the processing
93 of LC_MESSAGES.
94
96 Default.
97
99 The following formats shall be used when the LC_MESSAGES locale cate‐
100 gory specifies the POSIX locale. In other locales, the strings uid,
101 gid, euid, egid, and groups may be replaced with more appropriate
102 strings corresponding to the locale.
103 "uid=%u(%s) gid=%u(%s)\n", <real user ID>, <user-name>,
106 <real group ID>, <group-name>
107 If the effective and real user IDs do not match, the following shall be
109 inserted immediately before the '\n' character in the previous format:
110 " euid=%u(%s)"
113 with the following arguments added at the end of the argument list:
115 <effective user ID>, <effective user-name>
118 If the effective and real group IDs do not match, the following shall
120 be inserted directly before the '\n' character in the format string
121 (and after any addition resulting from the effective and real user IDs
122 not matching):
123 " egid=%u(%s)"
126 with the following arguments added at the end of the argument list:
128 <effective group-ID>, <effective group name>
131 If the process has supplementary group affiliations or the selected
133 user is allowed to belong to multiple groups, the first shall be added
134 directly before the <newline> in the format string:
135 " groups=%u(%s)"
138 with the following arguments added at the end of the argument list:
140 <supplementary group ID>, <supplementary group name>
143 and the necessary number of the following added after that for any
145 remaining supplementary group IDs:
146 ",%u(%s)"
149 and the necessary number of the following arguments added at the end of
151 the argument list:
152 <supplementary group ID>, <supplementary group name>
155 If any of the user ID, group ID, effective user ID, effective group ID,
157 or supplementary/multiple group IDs cannot be mapped by the system into
158 printable user or group names, the corresponding "(%s)" and name argu‐
159 ment shall be omitted from the corresponding format string.
160 When any of the options are specified, the output format shall be as
162 described in the OPTIONS section.
163
165 The standard error shall be used only for diagnostic messages.
166
168 None.
169
171 None.
172
174 The following exit values shall be returned:
175 0 Successful completion.
177 >0 An error occurred.
179
181 Default.
182 The following sections are informative.
184
186 Output produced by the -G option and by the default case could poten‐
187 tially produce very long lines on systems that support large numbers of
188 supplementary groups. (On systems with user and group IDs that are
189 32-bit integers and with group names with a maximum of 8 bytes per
190 name, 93 supplementary groups plus distinct effective and real group
191 and user IDs could theoretically overflow the 2048-byte {LINE_MAX} text
192 file line limit on the default output case. It would take about 186
193 supplementary groups to overflow the 2048-byte barrier using id -G).
194 This is not expected to be a problem in practice, but in cases where it
195 is a concern, applications should consider using fold -s before post-
196 processing the output of id.
197
199 None.
200
202 The functionality provided by the 4 BSD groups utility can be simulated
203 using:
204 id -Gn [ user ]
207 The 4 BSD command groups was considered, but it was not included
209 because it did not provide the functionality of the id utility of the
210 SVID. Also, it was thought that it would be easier to modify id to pro‐
211 vide the additional functionality necessary to systems with multiple
212 groups than to invent another command.
213 The options -u, -g, -n, and -r were added to ease the use of id with
215 shell commands substitution. Without these options it is necessary to
216 use some preprocessor such as sed to select the desired piece of infor‐
217 mation. Since output such as that produced by:
218 id -u -n
221 is frequently wanted, it seemed desirable to add the options.
223
225 None.
226
228 fold, logname, who
229 The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment
231 Variables, Section 12.2, Utility Syntax Guidelines
232 The System Interfaces volume of POSIX.1‐2017, getgid(), getgroups(),
234 getuid()
235
237 Portions of this text are reprinted and reproduced in electronic form
238 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
239 table Operating System Interface (POSIX), The Open Group Base Specifi‐
240 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
241 Electrical and Electronics Engineers, Inc and The Open Group. In the
242 event of any discrepancy between this version and the original IEEE and
243 The Open Group Standard, the original IEEE and The Open Group Standard
244 is the referee document. The original Standard can be obtained online
245 at http://www.opengroup.org/unix/online.html .
246 Any typographical or formatting errors that appear in this page are
248 most likely to have been introduced during the conversion of the source
249 files to man page format. To report such errors, see https://www.ker‐
250 nel.org/doc/man-pages/reporting_bugs.html .
251IEEE/The Open Group 2017 ID(1P)