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Linux 2.6 - man page for id (linux section 1posix)

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

       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 sup-
       ported by the underlying system (see the description of {NGROUPS_MAX} in the System Inter-
       faces  volume of IEEE Std 1003.1-2001), the supplementary group affiliations of the invok-
       ing 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.

       The id utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001,  Sec-
       tion 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" .

       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 IEEE Std 1003.1-2001, Section 8.2, Inter-
	      nationalization 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 interna-
	      tionalization variables.

	      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 argu-

	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error and informative messages written to stan-
	      dard output.

	      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  immedi-
       ately 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  supplemen-
       tary/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

       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 bar-
       rier 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.


       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  pro-
       vide  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 sub-
       stitution. 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 System Interfaces volume of IEEE Std 1003.1-2001, getgid(),
       getgroups(), getuid()

       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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					    ID(P)

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