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ID(1P) POSIX Programmer's Manual ID(1P)
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.
id — return user identity
id [user]
id −G [−n] [user]
id −g [−nr] [user]
id −u [−nr] [user]
If no user operand is provided, the id utility shall write the user
and group IDs and the corresponding user and group names of the
invoking process to standard output. If the effective and real IDs do
not match, both shall be written. If multiple groups are supported by
the underlying system (see the description of {NGROUPS_MAX} in the
System Interfaces volume of POSIX.1‐2008), the supplementary group
affiliations of the invoking process shall also be written.
If a user operand is provided and the process has appropriate
privileges, the user and group IDs of the selected user shall be
written. In this case, effective IDs shall be assumed to be identical
to real IDs. If the selected user has more than one allowable group
membership listed in the group database, these shall be written in
the same manner as the supplementary groups described in the
preceding paragraph.
The id utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported:
−G Output all different group IDs (effective, real, and
supplementary) only, using the format "%u\n". If there is
more than one distinct group affiliation, output each such
affiliation, using the format " %u", before the <newline>
is output.
−g Output only the effective group ID, using the format
"%u\n".
−n Output the name in the format "%s" instead of the numeric
ID using the format "%u".
−r Output the real ID instead of the effective ID.
−u Output only the effective user ID, using the format "%u\n".
The following operand shall be supported:
user The login name for which information is to be written.
Not used.
None.
The following environment variables shall affect the execution of id:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale
categories.)
LC_ALL If set to a non-empty string value, override the values of
all the other internationalization variables.
LC_CTYPE 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).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error and informative messages written to standard
output.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
Default.
The following formats shall be used when the LC_MESSAGES locale
category specifies the POSIX locale. In other locales, the strings
uid, gid, euid, egid, and groups may be replaced with more
appropriate strings corresponding to the locale.
"uid=%u(%s) gid=%u(%s)\n", <real user ID>, <user-name>,
<real group ID>, <group-name>
If the effective and real user IDs do not match, the following shall
be inserted immediately before the '\n' character in the previous
format:
" euid=%u(%s)"
with the following arguments added at the end of the argument list:
<effective user ID>, <effective user-name>
If the effective and real group IDs do not match, the following shall
be inserted directly before the '\n' character in the format string
(and after any addition resulting from the effective and real user
IDs not matching):
" egid=%u(%s)"
with the following arguments added at the end of the argument list:
<effective group-ID>, <effective group name>
If the process has supplementary group affiliations or the selected
user is allowed to belong to multiple groups, the first shall be
added directly before the <newline> in the format string:
" groups=%u(%s)"
with the following arguments added at the end of the argument list:
<supplementary group ID>, <supplementary group name>
and the necessary number of the following added after that for any
remaining supplementary group IDs:
",%u(%s)"
and the necessary number of the following arguments added at the end
of the argument list:
<supplementary group ID>, <supplementary group name>
If any of the user ID, group ID, effective user ID, effective group
ID, or supplementary/multiple group IDs cannot be mapped by the
system into printable user or group names, the corresponding "(%s)"
and name argument shall be omitted from the corresponding format
string.
When any of the options are specified, the output format shall be as
described in the OPTIONS section.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
Output produced by the −G option and by the default case could
potentially produce very long lines on systems that support large
numbers of supplementary groups. (On systems with user and group IDs
that are 32-bit integers and with group names with a maximum of 8
bytes per name, 93 supplementary groups plus distinct effective and
real group and user IDs could theoretically overflow the 2048-byte
{LINE_MAX} text file line limit on the default output case. It would
take about 186 supplementary groups to overflow the 2048-byte barrier
using id −G). This is not expected to be a problem in practice, but
in cases where it is a concern, applications should consider using
fold −s before post-processing the output of id.
None.
The functionality provided by the 4 BSD groups utility can be
simulated using:
id −Gn [ user ]
The 4 BSD command groups was considered, but it was not included
because it did not provide the functionality of the id utility of the
SVID. Also, it was thought that it would be easier to modify id to
provide the additional functionality necessary to systems with
multiple groups than to invent another command.
The options −u, −g, −n, and −r were added to ease the use of id with
shell commands substitution. Without these options it is necessary to
use some preprocessor such as sed to select the desired piece of
information. Since output such as that produced by:
id −u −n
is frequently wanted, it seemed desirable to add the options.
None.
fold(1p), logname(1p), who(1p)
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2008, getgid(3p),
getgroups(3p), getuid(3p)
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 .
IEEE/The Open Group 2013 ID(1P)
Pages that refer to this page: logname(1p)