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PASSWD(5)                     File Formats Manual                    PASSWD(5)

       passwd, group, shadow - user and group databases, shadow passwords


       /etc/passwd lists all the users of the system, and /etc/group lists all
       the groups the users may belong to.  Both files also contain  encrypted
       passwords,  numeric ID's etc.  Encrypted passwords may be hidden in the
       file /etc/shadow if extra protection is warranted.

       Each file is an text file containing one line per user or  group.   The
       data  fields  on  a  line  are  separated  by colons.  Each line in the
       password file has the following form:


       The name field is the login name of a user, it is up to  8  letters  or
       numbers  long  starting  with a letter.  The login name must be unique.
       The password field is  either  empty  (no  password),  a  13  character
       encrypted password as returned by crypt(3), or a login name preceded by
       two number signs (#) to index the shadow password file.  Anything  else
       (usually  *)  is  invalid.   The  uid  and  gid  fields are two numbers
       indicating the users user-id and group-id.  These id's do not  have  to
       be  unique,  there  may  be more than one name with the same id's.  The
       gecos field can be set by the user.  It  is  expected  to  be  a  comma
       separated  list  of personal data where the first item is the full name
       of the user.  The dir  field  is  the  path  name  of  the  users  home
       directory.   Lastly the shell field is the path name of the users login
       shell, it may be  empty  to  indicate  /bin/sh.   A  MINIX  3  specific
       extension  allows  the  shell  field  to  contain extra space separated
       arguments for the shell.

       Lines in the group file consist of four fields:


       The name field is the name of the group, same restrictions as  a  login
       name.   The  passwd  field may be used to let users change groups.  The
       gid field is a number telling the group-id.  The group-id is unique for
       a  group.   The mem field is a comma separated list of login names that
       are special members of the group.  If a system  supports  supplementary
       group  id's then a user's set of supplementary group id's is set to all
       the groups they are a member of.  If a  system  allows  one  to  change
       groups  then one can change to a group one is a member of without using
       the group's password.

       The shadow password file has precisely the same form  as  the  password
       file,  except that only the name or passwd fields are used as yet.  The
       other fields are zero or empty.  A password in the  password  file  may
       have  the form ##user to indicate the entry user in the shadow password
       file.  The password in this entry is then used  for  authentication  of
       the  user.   The shadow file can only be read by the privileged utility
       pwdauth(8), so that the encrypted passwords in the shadow file are kept
       secret, and thus safe from a dictionary attack.

   Special password and group file entries
       There  are  several  entries  in  the password and group files that are
       preallocated for current or future use.  All  id's  less  than  10  are
       reserved.  The special password file entries are:

              root:##root:0:0:Big Brother:/usr/src:
              daemon:*:1:1:The Deuce:/etc:
              uucp:*:5:5:UNIX to UNIX copy:/usr/spool/uucp:/usr/sbin/uucico
              news:*:6:6:Usenet news:/usr/spool/news:
              ftp:*:7:7:Anonymous FTP:/usr/ftp:
              ast:*:8:3:Andrew S. Tanenbaum:/usr/ast:

       The root id is of course the super user.  The daemon id is used by some
       daemons.  Some devices are protected so that  only  those  daemons  can
       access them.  The bin id owns all sources and most binaries.  The uucp,
       news and ftp id's are for serial line data transfer,  usenet  news,  or
       ftp  if so needed.  The nobody id is used in those cases that a program
       may not have any privileges at all.  The ast id is  the  honorary  home
       directory  for  Andrew  S.  Tanenbaum, the creator of MINIX 3.  You can
       also find the initial contents for a new home directory there.

       The special group file entries are:


       Groups with the same name as special user id are used with those  id's.
       The  operator  group is for the administrators of the system.  Users in
       this group are granted special privileges.   The  other  group  is  for
       ordinary  users.  The tty group is for terminal devices, and associated
       set-gid commands.  Same thing with the kmem group and memory devices.

       /etc/passwd    The user database.

       /etc/group     The group database.

       /etc/shadow    The shadow password file.

       login(1),  passwd(1),  su(1),   crypt(3),   getpwent(3),   getgrent(3),

       The  nobody and nogroup id's are likely to be renumbered to the highest
       possible id's once it is figured out what they are.

       Kees J. Bot (