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.1‐2017),
       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.

OPTIONS         top

       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

       -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

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

       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).

                 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.



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 format:

           " euid=%u(%s)"

       with the following arguments added at the end of the argument

           <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

           <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

           " groups=%u(%s)"

       with the following arguments added at the end of the argument

           <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 string.

       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

           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.1‐2017, Chapter 8,
       Environment Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2017, getgid(3p),
       getgroups(3p), getuid(3p)

COPYRIGHT         top

       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 .

       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               2017                            ID(1P)

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