I need to know what is UID mapping in linux/unix. What type of UID
mapping, I really don't know, all I know it has to do with users, but
if all UID mapping contexts can be explained it would be much better.

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Clarification of Question by daerian-ga on 23 Jun 2004 05:36 PDT

What is done in the process of mapping?

A UID, or "Unique Identifier", is a globally unique 32-bit number used
in a compound identifier to uniquely identify an object, file type,
etc. When users refer to "UID" they often mean UID3, the identifier
for a particular program.

See for more definitions of UID the Symbian online dictionary

http://www.symbian.com/developer/techlib/v70docs/SDL_v7.0/doc_source/GlobalGlossary/GlossaryDocumentU.html

The above answer is 100% wrong.  The URL given is for symbian, an OS
used primarily for cell-phones.

UID in linux/unix stands for User-ID, and is how the operating system
keeps track of individual users.  a UID is a unique 16 bit number
assigned to each user, and is specified for each user in the
/etc/passwd file.  The syntax of this file is (from the redhat man
page)
  
      There is one entry per line, and each line has the format:
                                                                                 
              account:password:UID:GID:GECOS:directory:shell
                                                                                 
       The field descriptions are:
                                                                                 
              account   the name of the user on the  system.   It
                        should not contain capital letters.
                                                                                 
              password  the encrypted user password or a star.
                                                                                 
              UID       the numerical user ID.
                                                                                 
              GID       the  numerical  primary group ID for this
                        user.
                                                                                 
              GECOS     This field is optional and only used  for
                        informational purposes.  Usually, it con?
                        tains the full user  name.   GECOS  means
                        General  Electric Comprehensive Operating
                        System, which has been  renamed  to  GCOS
                        when GE's large systems division was sold
                        to   Honeywell.    Dennis   Ritchie   has
                        reported: "Sometimes we sent printer out?
                        put or batch jobs to  the  GCOS  machine.
                        The gcos field in the password file was a
                        place to stash the  information  for  the
                        $IDENTcard.  Not elegant."
                                                                                 
              directory the user's $HOME directory.
                                                                                 
              shell     the  program  to  run at login (if empty,
                        use /bin/sh).  If set to  a  non-existing
                        executable,  the  user  will be unable to
                        login through login(1).


UID mapping could mean several things, but in general it means mapping
an external identifier to a UID, or vice versa.  The external
identifier could be a Windows account via the winbind program of the
Samba suite (windows<->linux fileserver), or NFS (which is a unix
based fileserver).  The basic idea idea behind this is to assign a
user-ID on the local unix/linux machine to a user that's authenticated
on a remote server (Windows fileserver or NFS).