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Linux System Administration
book

Linux System Administration

by Tom Adelstein, Bill Lubanovic
March 2007
Intermediate to advanced content levelIntermediate to advanced
304 pages
11h 12m
English
O'Reilly Media, Inc.
Content preview from Linux System Administration
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Chapter 8: Local Network Services
For instance, even after you have disabled Tom Adelstein’s password, he can get on
another computer somewhere and run a command such as:
$ ssh -f -N -L8000:intranet.yourcompany.com:80 my.domain.com
This forwards traffic to port 80 (the port on which a web server usually listens) on
your internal server.
Obviously, if your system offers SSH, you should remove authorized keys from the
appropriate directories (e.g., ~tadelste/.ssh or .~tadelste/.ssh2) in order to stop the
user from regaining access to his account this way:
$ cd .ssh
:~/.ssh$ ls
authorized_keys known_hosts
:~/.ssh$ rm authorized_keys
:~/.ssh$ ls
known_hosts
:~/.ssh$
Likewise, look for .shosts and .rhosts files in the user’s home directory (for example,
~tadelste/.shosts and ~tadelste/.rhosts).
Also, check to see if the user still has any processes running on the system. Such pro-
cesses might act as a backdoor to allow the user into your network. The following
command will tell you if a user currently has any running processes:
# ps aux |grep -i ^tadelste
Some other questions a system administrator might ask about a personal user who
has left the company include:
Could the user execute CGI scripts from his home directory or on one of the
company’s web servers?
Do any email forwarding files such as ~tadelste/.forward exist? Users can use for-
warders to send mail to their accounts and cause programs ...
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Publisher Resources

ISBN: 9780596009526Supplemental ContentCatalog PageErrata