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  IEEE Std 1003.1-2001), the supplementary group affiliations of the
       invoking process shall also be written.

       If a user operand is provided and the process has the 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  IEEE Std 1003.1-2001,
       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  IEEE Std 1003.1-2001, 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 postprocessing 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 System Interfaces volume of IEEE Std 1003.1-2001, getgid(),
       getgroups(), getuid()

COPYRIGHT

       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2003  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  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 .