A quick guide to Linux backup and recovery

IBM e-business architect Chris Walden is your guide through a nine-part developerWorks series on moving your operational skills from a Windows to a Linux environment. In this part, we take stock of what is on the system, and plan and implement regular backups with an eye to recovery as well as security.

Linux is a stable and reliable environment. But any computing system can have unforeseen events, such as hardware failures. Having a reliable backup of critical configuration information and data is part of any responsible administration plan. There is a wide variety of approaches to doing backups in Linux. Techniques range from very simple script-driven methods to elaborate commercial software. Backups can be done to remote network devices, tape drives, and other removable media. Backups can be file-based or drive-image based. There are many options available and you can mix and match your techniques to design the perfect backup plan for your circumstances.

What's your strategy?

There are many different approaches to backing up a system. For some perspectives on this, you may want to read the article "Introduction to Backing Up and Restoring Data" listed in the Resources section at the end of this article.

What you back up depends a lot on your reason for backing up. Are you trying to recover from critical failures, such as hard drive problems? Are you archiving so that old files can be recovered if needed? Do you plan to start with a cold system and restore, or a preloaded standby system?

What to back up?

The file-based nature of Linux is a great advantage when backing up and restoring the system. In a Windows system, the registry is very system specific. Configurations and software installations are not simply a matter of dropping files on a system. Therefore, restoring a system requires software that can deal with these idiosyncrasies. In Linux, the story is different. Configuration files are text based and, except for when they deal directly with hardware, are largely system independent. The modern approach to hardware drivers is to have them available as modules that are dynamically loaded, so kernels are becoming more system independent. Rather than a backup having to deal with the intricacies of how the operating system is installed on your system and hardware, Linux backups are about packaging and unpackaging files.

In general, there are some directories that you want to back up:

• /etc
  contains all of your core configuration files. This includes your network configuration, system name, firewall rules, users, groups, and other global system items.
• /var
  contains information used by your systems daemons (services) including DNS configurations, DHCP leases, mail spool files, HTTP server files, db2 instance configuration, and others.
• /home
  contains the default user home directories for all of your users. This includes their personal settings, downloaded files, and other information your users don't want to lose.
• /root
  is the home directory for the root user.
• /opt
  is where a lot of non-system software will be installed. IBM software goes in here. OpenOffice, JDKs, and other software is also installed here by default.

There are directories that you should consider not backing up.

• /proc
  should never be backed up. It is not a real-file system, but rather a virtualized view of the running kernel and environment. It includes files such as /proc/kcore, which is a virtual view of the entire running memory. Backing these up only wastes resources.
• /dev
  contains the file representations of your hardware devices. If you are planning to restore to a blank system, then you can back up /dev. However, if you are planning to restore to an installed Linux base, then backing up /dev will not be necessary.

The other directories contain system files and installed packages. In a server environment, much of this information is not customized. Most customization occurs in the /etc and /home directories. But for completeness, you may wish to back them up.

In a production environment where I wanted to be assured that no data would be lost, I would back up the entire system, except for the /proc directory. If I were mostly worried about users and configuration, I would back up only the /etc, /var, /home, and /root directories.