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ID(1P)                     POSIX Programmer's Manual                    ID(1P)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may dif-
       fer (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 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 Syn-
       tax 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  prece-
              dence 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  exam-
              ple, 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 writ-
              ten 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 correspond-
       ing 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 inte-
       gers 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 addi-
       tional 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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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 .



IEEE/The Open Group                  2003                               ID(1P)