Some system configuration files on Linux and what they do
This configuration file controls the system-wide environment variables. This contains the PATH variable that controls where binaries may be run from system-wide.
This file contains a message that will be visible above the login prompt on the virtual console. Usually this is auto-generated regularly containing system messages such as disk file-system check results and other useful information. Linux Mint 12 does this. You may modify this file to customize your system.
The rc.local file is a bash shell script that will be executed last during the system boot process after all of the other init scripts have completed. You may insert custom commands into this file that will be executed after every other command has finished. On my Linux Mint 12 system, this script in turn calls the /etc/rc.local script and runs any commands that it contains. Other systems could vary. if the /etc/rc.local shell script exists, then it would be the place to enter your custom commands.
This file contains your system hostname. You need to edit this file to set a new hostname and then use the sudo hostname mycomputer to set the new hostname, to mycomputer or what ever you wish it to be.
This configuration file contains the list of folders that contain library files such as libSDL.so and others. If you are installing software into the /usr/local folder from source, you will need to add that folder to the /etc/ld.so.conf file so that it will work properly when you type sudo ldconfig.
This folder contains scripts that will run certain commands as certain times, there are four cron directories that will run commands within hourly, daily, weekly or monthly. The format of the cron files consists of shell scripts that are easy to edit and add your own commands.
The /etc/hosts file contains a list of hosts and hostnames. An example is shown below. if you add a url such as I have at the bottom of this file, then it will be blocked. The system hostname is also defined at the top of the file.
127.0.0.1 localhost 127.0.1.1 deusexmachina # The following lines are desirable for IPv6 capable hosts ::1 ip6-localhost ip6-loopback fe00::0 ip6-localnet ff00::0 ip6-mcastprefix ff02::1 ip6-allnodes ff02::2 ip6-allrouters 0.0.0.0 doubleclick.net # blocked by mintNanny
This configuration file is where the ip addresses of the primary and secondary nameservers are defined. With modern Linux distributions this will be taken care of automatically and you should not have to worry about this file too much. This is only necessary if you are using a static route to connect to the Internet and then Internet nameservers would have to be defined here.
# Generated by NetworkManager domain Home search Home nameserver 192.168.1.1
The example above shows the configuration I am using on my Linux Mint 12 installation. It only contains the ip address of my router. The /etc/resolv.conf for my Debian Squeeze installation is exactly the same.
The hosts.deny file is a file that can contain a list of hosts that are not allowed network access to the system.
And the hosts.allow file of course, is a listing of hosts that are actually allowed to access the system over SSH or RSH, or any other network protocol.
Use this command to get more information about this.
ubuntu /etc $ man 5 hosts_access