PROLOG

       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

       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 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

       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 "%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 POSIX.1‐2008, 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 post-processing 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 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(), getgroups(), getuid()

COPYRIGHT

       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
       http://www.unix.org/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 .