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       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.


       id — return user identity


       id [user]

       id −G [−n] [user]

       id −g [−nr] [user]

       id −u [−nr] [user]


       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.


       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

       −r        Output the real ID instead of the effective ID.

       −u        Output only the effective user ID, using the format "%u\n".


       The following operand shall be supported:

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


       Not used.




       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

                 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.




       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:


       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.


       The standard error shall be used only for diagnostic messages.






       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.




       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.1‐2008, Chapter 8, Environment Variables, Section
       12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1‐2008, getgid(), getgroups(), getuid()


       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
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