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Essential System Administration, 3rd Edition

Top Five Open Source Packages for System Administrators

by Æleen Frisch, author of Essential System Administration, 3rd Edition

Every system administrator can do their job easier by using the myriad of excellent open source utilities and packages available. This is true whether or not the operating systems on the computers you administer are themselves open source. This is the first installment of a five-part series. In each installment I'll discuss one package from my current list of the most useful and widely applicable administrative tools. This week we'll start the countdown with number five. Check back here in the coming weeks for the next four installments.

#5: Amanda

Amanda stands for Advanced Maryland Automated Network Disk Archiver. It was developed at the University of Maryland. James da Silva was the initial author. Amanda is a network-based enterprise backup utility that includes features previously available only in expensive commercial packages. Amanda is not the equal of the best commercial backup software, but it can be useful for a variety of computing environments.

Amanda takes advantage of native backup software, including dump, GNU tar, and Samba's smbtar utility (for backing up Windows clients). Amanda provides the infrastructure to deploy these tools effectively across a network of systems that need to be backed up. It also provides the record keeping and other information-management capabilities, which are necessary for the package to be easy to use.

As you'd expect, Amanda supports common tape drives and other backup devices (including stackers and jukeboxes). It can take advantage of hardware compression features or compress archives prior to writing them to other media when the former is not available. Software compression may be performed either on the client system, where the data to be backed up lives, or on the backup server.

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By Æleen Frisch

Amanda can also perform full and incremental backups. In fact, Amanda will automatically select an incremental level based on its specified configuration parameters (more on this later).

Amanda has other nice features:

  • It provides excellent protection against accidental media overwriting.

  • It was designed with data security in mind. It uses its own network protocols, so it does not suffer from the security problems inherent in the traditional /etc/rmt approach used by dump (for example, using an .rhosts file in root's home directory). It can also use Kerberos authentication in addition to its own authentication scheme. And Kerberos-based encryption can also be used to protect the data as it is transmitted across the network.

How Amanda Works

Amanda allows backups from a network of clients to be sent to a single, designated backup server. It initiates the local backup operations according to its scheduling and other parameters. The resulting archives are then saved to tape or other media. Amanda can also use holding disks as intermediate storage for backup archives in order to maximize tape-write performance. That also ensures that data is backed up in spite of tape errors by allowing the backup set to be written to backup media at a later time.

Amanda uses a combination of full and incremental backups to save all of the data for which it is responsible, using the smallest possible daily backup set. It uses the following information to do so. (For simplicity, we'll assume that one backup run is performed every day):

  • The total amount of data to be backed up. Amanda computes this internally from the lists of items to be backed up.

  • The desired number of days between full backups (specified by the system administrator).

  • The percentage of the data that changes each day (estimated by the system administrator and then specified to Amanda).

Amanda's overall strategy is twofold: to complete a full backup of the data within each cycle and to be sure that all changed data has been backed up between full dumps. The traditional method of doing this is to perform the full backup, say, once a week, followed by incremental backups on the other days of the week. Amanda operates differently.

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