This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       Default.

       Default.

       Thefollowingsectionsareinformative.

       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(1POSIX)

       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 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, Section8.2, InternationalizationVariables 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.

       None.

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

       None.

       None.

       None.

       id — return user identity

       The following operand shall be supported:

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

       The id utility shall conform to the Base Definitions volume of POSIX.1‐2017, Section12.2, UtilitySyntaxGuidelines.

       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".

       None.

       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.

       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.

fold, logname, who

       The  Base  Definitions  volume  of  POSIX.1‐2017, Chapter8, EnvironmentVariables, Section12.2, UtilitySyntaxGuidelines

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

       The standard error shall be used only for diagnostic messages.

       Not used.

       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", <realuserID>, <user-name>,
               <realgroupID>, <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:

           <effectiveuserID>, <effectiveuser-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:

           <effectivegroup-ID>, <effectivegroupname>

       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:

           <supplementarygroupID>, <supplementarygroupname>

       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:

           <supplementarygroupID>, <supplementarygroupname>

       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.

       id [user]

       id -G [-n][user]

       id -g [-nr][user]

       id -u [-nr][user]