Unix - Linux
Using IPChains to Make a Packet-Filtering Firewall
1. Introduction
This tutorial describes how to use ipchains to make a simple packet-filtering firewall in Linux, mainly for the home user. We start with some background and theory on what packet filters can and cannot do, but the main focus is on selecting the ipchains rules. And although these notes use ipchains in Linux, […]
NIS on Linux
When running a local area network, one of the goals is usually to provide an environment to the users that make the network transparent. An important step for this is to keep vital data such as user account information (e.g. /etc/hosts, /etc/passwd and /etc/group files) synchronized between all hosts. For host name resolution, a […]
Tunneling NFS Through SSH
One method of encrypting NFS traffic over a network is to use the port-forwarding capabilities of ssh. However, as we shall see, doing so has a serious drawback if you do not utterly and completely trust the local users on your server.
The first step will be to export files to the localhost. For example, […]
The Portmapper
The portmapper keeps a list of what services are running on what ports. This list is used by a connecting machine to see what ports it wants to talk to access certain services.
The portmapper is not in as bad a shape as a few years ago but it is still a point of worry […]
nfsd mountd
On the server we can decide that we don’t want to trust any requests made as root on the client. We can do that by using the root_squash option in /etc/exports:
/home slave1(rw,root_squash)
This is, in fact, the default. It should always be turned on unless you have a very good reason to turn it off. […]
NFS in Unix & Linux
If your computer is on a LAN, the computer is probably set up to share files with other computers. Quite a few different schemes enable computers to use files on other machines. These schemes are named mostly with TLAs (Three Letter Acronyms) such as AFS, RFS, and NFS. Here, you find out about NFS (you’ll […]
NETWORK MAIL in Unix
There are several different ways of sending mail to users on other
systems. First of all, using the uucp and uux commands. Simply edit a text file
containing the message you wish to send, and uucp a copy of it to the remote
system. Then send it to the target user on that system using the uux command:
uux […]
DEBUGGING UUCP PROCEDURES
So, what if your transfer did not go through? Well, this section will
detail how to find out what went wrong, and how to correct the situation.
UULOG
—–
The uulog command is used to draw up a log of transactions with remote
systems. You can either draw up the entries by system name, or the name of the
user who […]
UUCP SYNTAX
Once you’ve completed an entry for the Unix system you wish to transfer
files with, you can issue the uucp command, and attempt the transfer. The
syntax to copy a file from the remote system is:
uucp remote![file pathname] [local pathname]
Where remote is the name of the system you wish to copy the file from, [file
pathname] is the […]
UNUSUAL LOGIN ENTRIES - UUCP
Sometimes, the login entry for a system might contain more than just
fields to expect the login prompt, send the username, expect the password
prompt, and send the password. For instance, if you have to go through a
multiplexer to get to the system, the login field would contain a subfield to
select the proper system from the multiplexer.
Sometimes, […]