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
13 id — return user identity
14
16 id [user]
17 id −G [−n] [user]
19 id −g [−nr] [user]
21 id −u [−nr] [user]
23
25 If no user operand is provided, the id utility shall write the user and
26 group IDs and the corresponding user and group names of the invoking
27 process to standard output. If the effective and real IDs do not match,
28 both shall be written. If multiple groups are supported by the underly‐
29 ing system (see the description of {NGROUPS_MAX} in the System Inter‐
30 faces volume of POSIX.1‐2008), the supplementary group affiliations of
31 the invoking process shall also be written.
32 If a user operand is provided and the process has appropriate privi‐
34 leges, the user and group IDs of the selected user shall be written. In
35 this case, effective IDs shall be assumed to be identical to real IDs.
36 If the selected user has more than one allowable group membership
37 listed in the group database, these shall be written in the same manner
38 as the supplementary groups described in the preceding paragraph.
39
41 The id utility shall conform to the Base Definitions volume of
42 POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
43 The following options shall be supported:
45 −G Output all different group IDs (effective, real, and supple‐
47 mentary) only, using the format "%u\n". If there is more
48 than one distinct group affiliation, output each such affili‐
49 ation, using the format " %u", before the <newline> is out‐
50 put.
51 −g Output only the effective group ID, using the format "%u\n".
53 −n Output the name in the format "%s" instead of the numeric ID
55 using the format "%u".
56 −r Output the real ID instead of the effective ID.
58 −u Output only the effective user ID, using the format "%u\n".
60
62 The following operand shall be supported:
63 user The login name for which information is to be written.
65
67 Not used.
68
70 None.
71
73 The following environment variables shall affect the execution of id:
74 LANG Provide a default value for the internationalization vari‐
76 ables that are unset or null. (See the Base Definitions vol‐
77 ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
78 ables for the precedence of internationalization variables
79 used to determine the values of locale categories.)
80 LC_ALL If set to a non-empty string value, override the values of
82 all the other internationalization variables.
83 LC_CTYPE Determine the locale for the interpretation of sequences of
85 bytes of text data as characters (for example, single-byte as
86 opposed to multi-byte characters in arguments).
87 LC_MESSAGES
89 Determine the locale that should be used to affect the format
90 and contents of diagnostic messages written to standard error
91 and informative messages written to standard output.
92 NLSPATH Determine the location of message catalogs for the processing
94 of LC_MESSAGES.
95
97 Default.
98
100 The following formats shall be used when the LC_MESSAGES locale cate‐
101 gory specifies the POSIX locale. In other locales, the strings uid,
102 gid, euid, egid, and groups may be replaced with more appropriate
103 strings corresponding to the locale.
104 "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)"
112 with the following arguments added at the end of the argument list:
114 <effective user ID>, <effective user-name>
116 If the effective and real group IDs do not match, the following shall
118 be inserted directly before the '\n' character in the format string
119 (and after any addition resulting from the effective and real user IDs
120 not matching):
121 " egid=%u(%s)"
123 with the following arguments added at the end of the argument list:
125 <effective group-ID>, <effective group name>
127 If the process has supplementary group affiliations or the selected
129 user is allowed to belong to multiple groups, the first shall be added
130 directly before the <newline> in the format string:
131 " groups=%u(%s)"
133 with the following arguments added at the end of the argument list:
135 <supplementary group ID>, <supplementary group name>
137 and the necessary number of the following added after that for any
139 remaining supplementary group IDs:
140 ",%u(%s)"
142 and the necessary number of the following arguments added at the end of
144 the argument list:
145 <supplementary group ID>, <supplementary group name>
147 If any of the user ID, group ID, effective user ID, effective group ID,
149 or supplementary/multiple group IDs cannot be mapped by the system into
150 printable user or group names, the corresponding "(%s)" and name argu‐
151 ment shall be omitted from the corresponding format string.
152 When any of the options are specified, the output format shall be as
154 described in the OPTIONS section.
155
157 The standard error shall be used only for diagnostic messages.
158
160 None.
161
163 None.
164
166 The following exit values shall be returned:
167 0 Successful completion.
169 >0 An error occurred.
171
173 Default.
174 The following sections are informative.
176
178 Output produced by the −G option and by the default case could poten‐
179 tially produce very long lines on systems that support large numbers of
180 supplementary groups. (On systems with user and group IDs that are
181 32-bit integers and with group names with a maximum of 8 bytes per
182 name, 93 supplementary groups plus distinct effective and real group
183 and user IDs could theoretically overflow the 2048-byte {LINE_MAX} text
184 file line limit on the default output case. It would take about 186
185 supplementary groups to overflow the 2048-byte barrier using id −G).
186 This is not expected to be a problem in practice, but in cases where it
187 is a concern, applications should consider using fold −s before post-
188 processing the output of id.
189
191 None.
192
194 The functionality provided by the 4 BSD groups utility can be simulated
195 using:
196 id −Gn [ user ]
198 The 4 BSD command groups was considered, but it was not included
200 because it did not provide the functionality of the id utility of the
201 SVID. Also, it was thought that it would be easier to modify id to pro‐
202 vide the additional functionality necessary to systems with multiple
203 groups than to invent another command.
204 The options −u, −g, −n, and −r were added to ease the use of id with
206 shell commands substitution. Without these options it is necessary to
207 use some preprocessor such as sed to select the desired piece of infor‐
208 mation. Since output such as that produced by:
209 id −u −n
211 is frequently wanted, it seemed desirable to add the options.
213
215 None.
216
218 fold, logname, who
219 The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
221 Variables, Section 12.2, Utility Syntax Guidelines
222 The System Interfaces volume of POSIX.1‐2008, getgid(), getgroups(),
224 getuid()
225
227 Portions of this text are reprinted and reproduced in electronic form
228 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
229 -- Portable Operating System Interface (POSIX), The Open Group Base
230 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
231 cal and Electronics Engineers, Inc and The Open Group. (This is
232 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
233 event of any discrepancy between this version and the original IEEE and
234 The Open Group Standard, the original IEEE and The Open Group Standard
235 is the referee document. The original Standard can be obtained online
236 at http://www.unix.org/online.html .
237 Any typographical or formatting errors that appear in this page are
239 most likely to have been introduced during the conversion of the source
240 files to man page format. To report such errors, see https://www.ker‐
241 nel.org/doc/man-pages/reporting_bugs.html .
242IEEE/The Open Group 2013 ID(1P)