passwd -- System Administration

Define system users

The file  /etc/passwd holds information about each  user who has permission
to use the COHERENT system.  This information is read by the commands login
and passwd whenever a user attempts  to log in, to ensure that that user is
really himself and not an impostor.

/etc/passwd holds one record for  each user; each record, in turn, consists
of seven colon-separated fields, as follows:

    name:password:user_id:group_id:comments:home_dir:shell

name is the user's login name.

password is his encrypted password.   If this field holds a single asterisk
`*', then the program login reads his password out of the file /etc/shadow.

user_id  is  a unique  number  that  is also  used  to  identify the  user.
group_id identifies the group to which the user belongs, if any.

comments  holds miscellaneous  data, such as  names, telephone  numbers, or
office numbers.

home_dir gives the user's home directory.

Finally, shell gives the program that  is first executed when the user logs
on; in most instances, this is an interactive shell (default, /bin/sh).

If you wish, you can set  additional passwords to control users who attempt
to log  into your system  remotely (that is,  via a modem).  You  can set a
different  remote-access password  for each  group of  users, based  on the
program invoked when they log in; for example, you can set one password for
the users who  log in and invoke uucico, and  another for the users who log
in and  invoke the interactive shells  ksh or sh. For details  on how to do
this, see the Lexicon entries d_passwd and dialups.

When a  user creates a file,  that file is ``owned''  by him.  For example,
whenever user joe create a file, that file is ``owned'' by joe; and joe has
user-level  permissions  on that  file.   The superuser  root  can use  the
command chown to  change the ownership of a file  from one user to another.
For details on this command, see its entry in the Lexicon.

See Also

Administering COHERENT,
chown,
passwd [command]

Notes

/etc/passwd can be read by anyone:  if access to it were refused to a user,
he could not  log on.  Thus, the passwords encrypted  within it can be read
and copied  by anyone, and so may be  vulnerable to brute-force decryption.
For this  reason, close attention should be paid  to passwords: they should
not be common words or names, preferably mix cases or use unique spellings,
and be at least six characters long.

© 2012 by Stephen A. Ness