ID(1P) POSIX Programmer's Manual ID(1P)
PROLOG
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.
NAME
id -- return user identity
SYNOPSIS
id [user]
id -G [-n] [user]
id -g [-nr] [user]
id -u [-nr] [user]
DESCRIPTION
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 underly-
ing system (see the description of {NGROUPS_MAX} in the System Inter-
faces 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 privi-
leges, 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.
OPTIONS
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 supple-
mentary) only, using the format "%u\n". If there is more
than one distinct group affiliation, output each such affili-
ation, using the format " %u", before the <newline> is out-
put.
-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".
OPERANDS
The following operand shall be supported:
user The login name for which information is to be written.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of id:
LANG Provide a default value for the internationalization vari-
ables that are unset or null. (See the Base Definitions vol-
ume of POSIX.1-2008, Section 8.2, Internationalization Vari-
ables 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.
ASYNCHRONOUS EVENTS
Default.
STDOUT
The following formats shall be used when the LC_MESSAGES locale cate-
gory 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 argu-
ment 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.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
Output produced by the -G option and by the default case could poten-
tially 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.
EXAMPLES
None.
RATIONALE
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 pro-
vide 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 infor-
mation. Since output such as that produced by:
id -u -n
is frequently wanted, it seemed desirable to add the options.
FUTURE DIRECTIONS
None.
SEE ALSO
fold, logname, who
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(), getgroups(),
getuid()
COPYRIGHT
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 Electri-
cal 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.ker-
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 ID(1P)
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