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Full Discussion: How the /etc/passwd file is written when user does not have permission
Top Forums UNIX for Dummies Questions & Answers How the /etc/passwd file is written when user does not have permission Post 302223666 by buffoonix on Monday 11th of August 2008 04:25:18 AM
Old 08-11-2008
Does this really smell like homework?
I would have taken it for a legitimate newbie question,
especially since it was posted in the Dummies section.

Have a look at the user interface's binary to change one's password
which is the command passwd
Code:
$ ls -l /usr/bin/passwd 
-rwsr-xr-x 1 root root 22960 Jul 17  2006 /usr/bin/passwd

As you can see from the owner's (i.e. root) perm bits instead of the usual x
for execute there appears an s, the so called suid bit (that's what era referred to).
This means that although most of the times executed by ordinary users,
the command actually runs under the effective uid of root who is the only one on the system (normally) who is allowed to write to the file /etc/passwd.

If you look at the perms of the ping command you will find another suid binary
because ordinary users are not allowed to emit ICMP echo request packets.

Because of the security implications those elevated privileges impose
you generally will find only very few suid enabled executables on most Unix systems.
And their number should be observed in e.g. security audits or when hardening a system.
 

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LEARN ABOUT DEBIAN

cvsd-passwd

cvsd-passwd(8)						      System Manager's Manual						    cvsd-passwd(8)

NAME

       cvsd-passwd - generate password entries for repositories

SYNOPSIS

       cvsd-passwd REPOS [+|-]NAME...

DESCRIPTION

       cvsd-passwd adds, updates or deletes users from repository passwd files for use with cvsd.

OPTIONS

       REPOS  Specify  the  directory in which the repository is located. This argument can be the top of the repository, the CVSROOT directory or
	      even the passwd file in the CVSROOT directory.

       [+]USER[:SUSER]
	      Add or update the user to the CVSROOT/passwd file.  If the user does not exist a password for the user is  asked	and  the  user	is
	      added for use with cvsd.	If the user already exists a password for is asked and the password field is modified.

	      The :SUSER part can be user to change or set mapping to a system user.  If you do not specify anything, a reasonable default is used
	      based upon your cvsd configuration.  If you don't want to map the user to any specified system user you can specify an  empty  SUSER
	      and use 'USER:'.

       -USER  Remove the user from the CVSROOT/passwd file.

EXAMPLES

       Add an anoncvs user to access the given repository:
	   cvsd-passwd /var/lib/cvsd/myrepos +anoncvs
       If the user already exists, change the password.

       Remove a user from the repository passwd list:
	   cvsd-passwd /var/lib/cvsd/myrepos -foo

       Add a user and specify that cvs should remap this user to the joe system user:
	   cvsd-passwd /var/lib/cvsd/myrepos joecvs:joe
       Note that the user joe should be known in the system passwd file and that cvsd should be run as root or user joe for this to work.

SEE ALSO

       cvsd(8)

AUTHOR

       Arthur de Jong <arthur@arthurdejong.org>.

Version 1.0.24							     Jun 2012							    cvsd-passwd(8)
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