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id(P) id(P)
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 out-
put. 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
IEEE Std 1003.1-2001), the supplementary group affilia-
tions of the invoking process shall also be written.
If a user operand is provided and the process has the
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 member-
ship listed in the group database, these shall be writ-
ten 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 IEEE Std 1003.1-2001, 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 affil-
iation, 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 for-
mat "%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 internationaliza-
tion variables that are unset or null. (See the
Base Definitions volume of IEEE Std 1003.1-2001,
Section 8.2, Internationalization Variables for
the precedence of internationalization variables
used to determine the values of locale cate-
gories.)
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 mes-
sages 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 category specifies the POSIX locale. In other
locales, the strings uid, gid, euid, egid, and groups
may be replaced with more appropriate strings corre-
sponding 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.
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 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 con-
sider using fold -s before postprocessing 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 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.
FUTURE DIRECTIONS
None.
SEE ALSO
fold , logname , who , the System Interfaces volume of
IEEE Std 1003.1-2001, getgid(), getgroups(), getuid()
COPYRIGHT
Portions of this text are reprinted and reproduced in
electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute of Electrical and Electronics Engineers, Inc and
The Open Group. 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.open-
group.org/unix/online.html .
POSIX 2003 id(P)
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