Wednesday, 3 April 2013

Linux (Red Hat/Centos) post Install tasks

Linux (Red Hat/Centos) post Install tasks


I assume if you are setting up a Linux server, there must be a purpose, a new service you need to deploy, you want to learn it, you want to test it etc.

 

Once you have successfully installed your Red Hat/Centos server, there are few things you need to set, and think ahead.

 

I recommend before you set to install your new server to take some time to think it through.

There are some questions you need to think about, some of them below:

Note: By no means is this a comprehensive list, it is just some ideas.

 

1.       What is the purpose of the (new) server?

·          Test, Production, learning

2.       What application the (new) server will host?

·          Web, DNS, FTP, Mail, Custom app

3.       Will the server face the Internet?

·         web app, DNS

4.       How will it be exposed to the Internet?

a.       Directly (with a Public IP)

Via a proxy (Behind a proxy sock or similar)

b.      Behind a physical Firewall (Juniper, Cisco) Being NATted

c.       Positioning of the server on your network (LAN v DMZ)

Note: If your server needs to face the Internet, I think it is a good idea to isolate it from the LAN.

5.       What Partition layout and how big each should be

I think it is always a good idea to separate the following File Systems:

                /boot – normally 100MB – you can give more if you want to

                /tmp - depending on the system 2GB is a good starting point

                /swap – depending how much memory you have etc.

                Note: Some guys like giving twice the RAM memory size. If you have enough

Memory you will not need to worry about /swap too much

                /var – a good starting point is 5GB

                /home – depending if you will be hosting users and what your users will be doing

                /usr – 5-10GB is ok (it all depends, how the server will be used, where the

                Application will be installed etc.

/ (the root file system is very important not to run out of space here.

Note: Depending on the server’s role, the level of security you need to apply to certain partitions differ. i.e /tmp need extra care if you have web applications.

 

6.       What services should be left running

I am in favour of, if the service is not needed, then it should not be enabled.

This is a good practice, for stability and security.

7.       What IP address will be assigned to the server

If your ISP provided you with a single Public IP, then you have no choice. If you on the other hand you will be protecting the server behind a Firewall. Just plan it, use private IPs.

Place the server in a different sub-net; I tend to use 192.168.0.0/24 or 172.16.0.0/24.

Split the range into separate blocks, assign blocks to different servers and services. For example: 192.168.1.1-10 to web servers, 192.168.11-30 to database servers etc.

8.       What name to give the server

There are many ways to create a name convention

9.       What Name servers to use

10.   The Default Gateway to access the Internet

11.   If you need to keep DATE/TIME in sync

 

I think I covered most things, but there is many more, depending how secure and reliable you want your server to be.

 

I start setting up the server name, see below:

Set Hostname

# cd /etc

# vi hosts

192.168.1.34  centos63 centos63.adlinux.int

 

# vi /etc/sysconfig/network (this is where you set the server name and the default gateway)

NETWORKING=yes

HOSTNAME=centos63.adlinux.int

GATEWAY=192.168.1.1

 

Set IP address

# vi /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE="eth0"

BOOTPROTO="static"

NM_CONTROLLED="no"

ONBOOT="yes"

TYPE="Ethernet"

IPADDR=192.168.1.34

NETMASK=255.255.255.0

 

Set Name servers

# vi /etc/resolv.conf

domain adlinux.int

search adlinux.int

nameserver 192.168.1.22

 

Just reboot your Linux server and all the changes will take affect at boot time.

 

There are many files which need to be set; it all depends on the role, of the server as already pointed out above. The configuration above is just the basic network configuration to get you up and running.

Don’t forget to plan, think it through, break it down into smaller tasks and take note of your plan, document it well otherwise when you need to revisit the configuration, you may not remember the reasons for setting things up the way you did.

 

Advice:

1.       Planning

2.       Documentation

3.       Backup

4.       Roll back

 

 

Hope you enjoy it.

 

By Renato de Oliveira

 

 

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