Chattr is one of those often under used permission utils that most people
don't even know about.  But chattr has many uses, you just have to use
your imagination.

Now don't quote me on this but that chattr man page says that it is for
ext2 file systems and is part of the e2fsprogs, so it probably doesn't 
exist on *BSD and the like (although they may have simalar utils).  If 
I'm wrong let me know and I will up date this.

A normal ls -l will not show the attributes that chattr sets as it is a 
ext2 file system thing and ls doesn't have to be run on an ext2 file system.
So we use the aptly named lsattr program to see them.

~#: lsattr

-------- ./somedir
-------- ./somefile

Now if you can't tell that these two things do not have any chattr permissions
set perhaps you are reading the wrong txt file.

Chattr as with chown only has a few otions so it's not as complex a permssion
changer as chmod, but there are still a few to choose from.

Changing the chattr permissions on a file or directory is the same as chmod
'+' to add one and '-' to remove one with one exception, '=' setting this
will remove all other chattr settings and make this one the only one.

The options you can use with chattr are:

A (Access time or atime)
A file with this set does not have it's atime update everytime it is accessed

a (append)
A file with this set can only be appended to, eg you can't remove any content
from this file, root is the only user that can set or clear this

c (compress)
A quite under used but highly useful attribute this will gzip compress a file
on the harddrive to make it smaller.  Access this file will start an on the
fly [de]compression so that no modifications to existing tools is required.

d (dump)
A bit missleading something set with this is over looked for backup when using
the dump utility (check the dump man page for more information)

i (immune) (best guess on a name)
A file set with this can not be modified, deleted renamed have symbolic links
applied to it or appended to.  Only the root user can set or clear this.  On
a side note if your /etc/passwd is rarely changed this might be a good
attribute to set for it as symbolic links to /etc/passwd have been a source
of exploits.  However this denies users the ability to change their password
for them self so you may wish to inform them of this

s (?)
With this set this file is deleted it's blocks on disk are zeroed out and 
rewritten back to disk.  Effectivly making recovering this file impossible

S (Synchronous)
Linux buffer disk activity to speed things up and only writes to disk when 
it's buffer are full or it has a spare moment to do so (usually the latter)
So if you set this attribute and you modify the file it's contents are
written back to disk right away without waiting in the buffer.  Again this
might be a useful addtion to /etc/passwd just in case.

u (undelete)
Setting this file will get the ext2 code to "save" the files contents, allowing
root to later undelete the file if user so wishes.

Some quick examples of it's use are:

chattr +i somefile -> ----i--- ./somefile
chattr +A somefile -> ----i--A ./somefile
chattr +s somefile -> s---i--A ./somefile
chattr -s somefile -> ----i--A ./somefile
chattr =i somefile -> ----i--- ./somefile


The chattr man pages state that 'u' and 'c' are not yet supported by the
0.5a ext2 fs code, however this is older information and I have not yet 
verified this.  I also states that 'A' is still being worked on

Notes:  Unlike chmod settings which have no effect on the root user chattr
settings do affect the root user so you must make allowence for this if
you go on a chattr spree and start changing things.

Chattr also supports the -R (recursive) for directories.