id(1p) — Linux manual page


ID(1P)                    POSIX Programmer's Manual                   ID(1P)

PROLOG         top

       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         top

       id — return user identity

SYNOPSIS         top

       id [user]

       id −G [−n] [user]

       id −g [−nr] [user]

       id −u [−nr] [user]

DESCRIPTION         top

       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.

OPTIONS         top

       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

       −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         top

       The following operand shall be supported:

       user      The login name for which information is to be written.

STDIN         top

       Not used.

INPUT FILES         top



       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

       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).

                 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

       NLSPATH   Determine the location of message catalogs for the
                 processing of LC_MESSAGES.



STDOUT         top

       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

           " 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:


       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

       When any of the options are specified, the output format shall be as
       described in the OPTIONS section.

STDERR         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.



       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.

EXAMPLES         top


RATIONALE         top

       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.



SEE ALSO         top

       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)

COPYRIGHT         top

       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 .

       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 .

IEEE/The Open Group                 2013                              ID(1P)

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