Maintaining your Linux OS
Overview
Basic
management
Passwords
Checking
storage space
Checking
processes
Managing
users
Shutting down
and restarting your computer
Automating
tasks
Linux file management
File compression and
archiving tools
File managers
File
splitters
Linux networking
Getting
started
MAC and IP
addresses
Domain names
Adding a Linux
host to an existing network
Building a
private network
Configuring the network
interface
Security
Uninstalling Linux
Summary
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Security
Whatever anyone tells you about security, unfortunately the only
way to be completely sure that your computer is safe from a
security breach is to disconnect it from the Internet and never to
load any program or document that supports macros. This is clearly
not going to be practical and so the answer is to find a number of
ways of making security breaches to your networked computer more
difficult. A number of possibilities are listed below.
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It is possible to set up your system so that logins to your
machine can only be done from other computers on your own local
network and not from machines on the Internet. To do this you need
to look at the files /etc/hosts.allow and
/etc/hosts.deny.
-
You should make sure that your root password is secure. It is no
use using short dictionary words, as these can easily be broken
using simple password generator programs. Do not be tempted to set
up users with blank passwords; it might seem like a good idea at
the time, but this is very insecure. Finally, if you have more than
one server, then you should make sure that the passwords are
different for each. This ensures that if one machine is breached
you do not compromise the whole system.
-
Denying host access will not completely secure your system as it
is possible to intercept messages from your machine, strip out the
important data such as the identifiers of other machines on your
network, and then by a mechanism known as 'spoofing' pretend to be
another machine. The best way of getting around this problem is to
use the ssh tool when connecting to other machines in
your network. This ensures that the data packets sent between
machines are encrypted. If you use ssh-level security for all your
network traffic, then you make spoofing much harder
(ssh can be downloaded for free from www.ssh.com).
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Another way of maintaining security is to monitor the system log
files. In the directory /var/log you will find a
number of files in which information regarding all the system and
network information on your machine is stored. While this
information takes a bit of interpretation, you will find that you
can use it to study most of the activity on your system and on your
network.
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Firewalls provide a means of protection between private devices
such as computers or local networks and the wider Internet. The
simplest form of firewall protection is to set up a Linux machine
with a single Internet connection (through an Ethernet card or
modem) which acts as a buffer between the Internet and any local
network. This machine then blocks direct communication between the
local network and the Internet (in either direction). The advantage
of this approach is that anything inside the firewall is protected;
the disadvantage is that it is a little complicated to set up - you
need to configure the machine for two Ethernet cards and then
connect the two cards through an IP-chain to
filter the data between them.
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