Open-Source Backups Using Amanda

Those of us who have received the call can feel the tension and nervous tone in the caller's voice when he or she asks, “How good are the backups?” A failed disk, files deleted by mistake, a disgruntled coworker or, worse, a security breach all can be times when you need to depend on backups.

Data probably is the most important element in computing, but in too many cases I see data backups overlooked or approached in such a carefree manner that I shiver. To this end, this article discusses the University of Maryland's Amanda (advanced Maryland automatic disk archiver) backup software, a relatively easy-to-use disk archiver built upon native dump and/or GNU tar tools. I often feel Amanda does not get the respect it deserves in a Linux/UNIX cross-platform environment. I confidently can say, however, that Amanda is a reliable platform for many Linux and UNIX users who are comfortable with a command-line interface.

I began using Amanda approximately three years ago as a backup platform in an educational environment. Working in an educational and research environment provides many challenges when it comes to backups. Many technical professionals and hobbyists face these same challenges related to their own backups. The challenges include the lack of a budget large enough to include backup software, a wide variety of OSes and distributions to back up and limited human resources to accomplish all the backups.

For myself and others, the ideal solution would be to have a central backup server that can accommodate multiple configurations as well as multiple backup tape devices, while requiring a minimum amount of time and resources. Amanda meets these requirements and and many more.

Installing Amanda is a straightforward process. Whether you install from source or a binary package, you need to have a backup user and a backup group. You also need to enable disk access permission to the Amanda user and backup group. The default install from RPM takes care of this step for you, adding Amanda as a user and including Amanda as a member of the disk group.

With a default installation of Amanda, the majority of your server configuration files are placed in subdirectories of /etc/amanda/, for example /etc/amanda/DailySet1. The minimal files to place in /etc/amanda/<amanda_config> are the amanda.conf file and the disklist file. The amanda.conf file holds the configuration settings for that backup run and the disklist file holds a list of disks to be backed up with that configuration. Additional files, which are placed in /var/lib/amanda by default, include index files, log file, current info files as well as additional configuration files. If the administrator prefers, the executable files are normally placed in /usr/sbin and include amdump, the actual Amanda dump program; amcheck, the Amanda pre-dump check utility; amverify, the Amanda utility to verify the integrity of the dumps; amrecover and amrestore, the recovery programs; and various other Amanda utilities.

Once Amanda is installed, amcheck and amdump search the default config directory of /etc/amanda/<configuration> for the configuration files unless it is told to do otherwise. Within /etc/amanda, you need a directory for each configuration to be run. The amanda.conf file may appear somewhat complex, but it is, in fact, rather self explanatory. It contains plenty of documentation, and once read it is easy to interpret and customize for your environment. On both the client and server end, inetd.conf or xinetd.conf must contain entries for Amanda. On the server, you also need to have entries for the index server, amandaidx, and the tape server, amidxtaped (Listing 1). In addition to the xinetd settings, for each host within the Amanda user's home directory, an .amandahosts file is required. This file defines each host and the user from that host who is allowed to access the machine (Listing 2). Particular attention should be paid to the permissions on the Amanda user's home directory and the accompanying files, for obvious security reasons.