man id – Man page for id

June 1, 2007 – 1:41 am

ID


Section: POSIX Programmer’s Manual (P)
Updated: 2003
Index
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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 underlying system (see the description
of {NGROUPS_MAX} in the System Interfaces volume of
IEEE Std 1003.1–2001), the supplementary group affiliations 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 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 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 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"
.



 

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 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 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
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.
 

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 consider 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 Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001–2003 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 .



 

Index



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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  5. man setresuid – Man page for setresuid
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  8. man seteuid – Man page for seteuid
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