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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017),
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.1‐2017, 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.1‐2017, 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.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1‐2017, getgid(3p),
getgroups(3p), getuid(3p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute 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.opengroup.org/unix/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 2017 ID(1P)
Pages that refer to this page: logname(1p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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