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
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 IEEE Std 1003.1-2001), the supplementary group affilia‐
31 tions of the invoking process shall also be written.
32 If a user operand is provided and the process has the appropriate priv‐
34 ileges, the user and group IDs of the selected user shall be written.
35 In this case, effective IDs shall be assumed to be identical to real
36 IDs. 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 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
43 The following options shall be supported:
45 -G Output all different group IDs (effective, real, and supplemen‐
47 tary) only, using the format "%u\n" . If there is more than one
48 distinct group affiliation, output each such affiliation, using
49 the format " %u", before the <newline> is output.
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
62 The following operand shall be supported:
63 user The login name for which information is to be written.
65
68 Not used.
69
71 None.
72
74 The following environment variables shall affect the execution of id:
75 LANG Provide a default value for the internationalization variables
77 that are unset or null. (See the Base Definitions volume of
78 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
79 ables for the precedence of internationalization variables used
80 to determine the values of locale categories.)
81 LC_ALL If set to a non-empty string value, override the values of all
83 the other internationalization variables.
84 LC_CTYPE
86 Determine the locale for the interpretation of sequences of
87 bytes of text data as characters (for example, single-byte as
88 opposed to multi-byte characters in arguments).
89 LC_MESSAGES
91 Determine the locale that should be used to affect the format
92 and contents of diagnostic messages written to standard error
93 and informative messages written to standard output.
94 NLSPATH
96 Determine the location of message catalogs for the processing of
97 LC_MESSAGES .
98
101 Default.
102
104 The following formats shall be used when the LC_MESSAGES locale cate‐
105 gory specifies the POSIX locale. In other locales, the strings uid,
106 gid, euid, egid, and groups may be replaced with more appropriate
107 strings corresponding to the locale.
108 "uid=%u(%s) gid=%u(%s)\n", <real user ID>, <user-name>,
111 <real group ID>, <group-name>
112 If the effective and real user IDs do not match, the following shall be
114 inserted immediately before the '\n' character in the previous format:
115 " euid=%u(%s)"
118 with the following arguments added at the end of the argument list:
120 <effective user ID>, <effective user-name>
123 If the effective and real group IDs do not match, the following shall
125 be inserted directly before the '\n' character in the format string
126 (and after any addition resulting from the effective and real user IDs
127 not matching):
128 " egid=%u(%s)"
131 with the following arguments added at the end of the argument list:
133 <effective group-ID>, <effective group name>
136 If the process has supplementary group affiliations or the selected
138 user is allowed to belong to multiple groups, the first shall be added
139 directly before the <newline> in the format string:
140 " groups=%u(%s)"
143 with the following arguments added at the end of the argument list:
145 <supplementary group ID>, <supplementary group name>
148 and the necessary number of the following added after that for any
150 remaining supplementary group IDs:
151 ",%u(%s)"
154 and the necessary number of the following arguments added at the end of
156 the argument list:
157 <supplementary group ID>, <supplementary group name>
160 If any of the user ID, group ID, effective user ID, effective group ID,
162 or supplementary/multiple group IDs cannot be mapped by the system into
163 printable user or group names, the corresponding "(%s)" and name argu‐
164 ment shall be omitted from the corresponding format string.
165 When any of the options are specified, the output format shall be as
167 described in the OPTIONS section.
168
170 The standard error shall be used only for diagnostic messages.
171
173 None.
174
176 None.
177
179 The following exit values shall be returned:
180 0 Successful completion.
182 >0 An error occurred.
184
187 Default.
188 The following sections are informative.
190
192 Output produced by the -G option and by the default case could poten‐
193 tially produce very long lines on systems that support large numbers of
194 supplementary groups. (On systems with user and group IDs that are
195 32-bit integers and with group names with a maximum of 8 bytes per
196 name, 93 supplementary groups plus distinct effective and real group
197 and user IDs could theoretically overflow the 2048-byte {LINE_MAX} text
198 file line limit on the default output case. It would take about 186
199 supplementary groups to overflow the 2048-byte barrier using id -G).
200 This is not expected to be a problem in practice, but in cases where it
201 is a concern, applications should consider using fold -s before post‐
202 processing the output of id.
203
205 None.
206
208 The functionality provided by the 4 BSD groups utility can be simulated
209 using:
210 id -Gn [ user ]
213 The 4 BSD command groups was considered, but it was not included
215 because it did not provide the functionality of the id utility of the
216 SVID. Also, it was thought that it would be easier to modify id to pro‐
217 vide the additional functionality necessary to systems with multiple
218 groups than to invent another command.
219 The options -u, -g, -n, and -r were added to ease the use of id with
221 shell commands substitution. Without these options it is necessary to
222 use some preprocessor such as sed to select the desired piece of infor‐
223 mation. Since output such as that produced by:
224 id -u -n
227 is frequently wanted, it seemed desirable to add the options.
229
231 None.
232
234 fold, logname, who, the System Interfaces volume of
235 IEEE Std 1003.1-2001, getgid(), getgroups(), getuid()
236
238 Portions of this text are reprinted and reproduced in electronic form
239 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
240 -- Portable Operating System Interface (POSIX), The Open Group Base
241 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
242 Electrical and Electronics Engineers, Inc and The Open Group. In the
243 event of any discrepancy between this version and the original IEEE and
244 The Open Group Standard, the original IEEE and The Open Group Standard
245 is the referee document. The original Standard can be obtained online
246 at http://www.opengroup.org/unix/online.html .
247IEEE/The Open Group 2003 ID(1P)