How to avoid overwrite the passwd and shadow file

[sun_os]

Dear All,

I have no idea to do so the below questions:

1. I add the users and set the password. But I want to avoid someone to overwrite the shadow when log on as root .
2. The users telnet the server, browser the directory. But the telnet connect is time out. What is the first thing I need to check? 

Thanks

[Rob Pomeroy]

I want to avoid someone to overwrite the shadow when log on as root

You can't.  root is omnipotent, by definition.

[sun_os]

Oh! I want to aviod two root users to edit the /etc/passwd , I don't want to set the acl to complicate the permission on the file.

[Rob Pomeroy]

I think your best bet is going to be to set up other administrative users and maybe even prevent root from logging on (other than at the console?).  I assume you're thinking of SELinux's capabilities - there are some good walkthroughs >here<.