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Copy file name to clipboardExpand all lines: docs/books/admin_guide/09-backups.md
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@@ -25,34 +25,34 @@ In this chapter you will learn how to back up and restore your data with Linux.
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!!! Note
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Throughout this chapter the command structures use "device" to specify both a target location for backup, and the source location when restoring. The device can be either external media or a local file. You should get a feel for this as the chapter unfolds, but you can always refer back to this note for clarification if you need to.
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Throughout this chapter, the command structures use "device" to specify both a target location for backup and the source location when restoring. The device can be either external media or a local file. You should get a feel for this as the chapter unfolds, but you can always refer back to this note for clarification if you need to.
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The backup will answer a need to conserve and restore data in a sure and effective way.
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The backup will answer the need to conserve and restore data effectively.
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The backup allows you to protect yourself from the following:
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***Destruction**: voluntary or involuntary. Human or technical. Virus, ...
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***Deletion**: voluntary or involuntary. Human or technical. Virus, ...
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***Integrity**: data becomes unusable.
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No system is infallible, no human is infallible, so to avoid losing data, it must be backed up to be able to restore after a problem.
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No system is infallible, and no human is infallible, so to avoid losing data, it must be backed up so that it can be restored after a problem.
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The backup media should be kept in another room (or building) than the server so that a disaster does not destroy the server and the backups.
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In addition, the administrator must regularly check that the media are still readable.
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## Generalities
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There are two principles, the **backup** and the **archive**.
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There are two principles: the **backup** and the **archive**.
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* The archive destroys the information source after the operation.
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* The backup preserves the source of information after the operation.
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These operations consist of saving information in a file, on a peripheral or a supported media (tapes, disks, ...).
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These operations consist of saving information in a file, on a peripheral, or on a supported media (tapes, disks, etc.).
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### The process
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Backups require a lot of discipline and rigor from the system administrator. System administrator need to consider the following issues before performing backup operations:
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Backups require a lot of discipline and rigor from the system administrator. System administrators need to consider the following issues before performing backup operations:
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* What is the appropriate medium?
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* What should be backed up?
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!!! Tip
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Before a system change, it can be useful to make a backup. However, there is no point in backing up data every day that is only changed every month.
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Before a system change, it can be useful to make a backup. However, there is no point in backing up data every day that only changes every month.
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### Restoration methods
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Depending on the utilities available, it will be possible to perform several types of restorations.
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Depending on the utilities available, performing several types of restorations will be possible.
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***Complete restoration**: trees, ...
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***Selective restoration**: part of tree, files, ...
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It is possible to restore a whole backup, but it is also possible to restore only a part of it. However, when restoring a directory, the files created after the backup are not deleted.
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It is possible to restore a whole backup or only a part of it. However, when restoring a directory, the files created after the backup are not deleted.
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!!! Tip
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To recover a directory as it was at the time of the backup, it is necessary to completely delete its contents before launching the restoration.
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To recover a directory as it was before the backup, it is necessary to completely delete its contents before launching the restoration.
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### The tools and related technologies
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### Naming convention
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The use of a naming convention makes it possible to quickly target the contents of a backup file and thus avoid hazardous restorations.
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The use of a naming convention allows one to quickly target the contents of a backup file and thus avoid hazardous restorations.
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* name of the directory;
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* utility used;
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!!! Tip
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The name of the backup must be an explicit name.
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The name of the backup must be explicit.
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!!! Note
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The notion of extension under Linux does not exist. In other words, our use of extensions here is for the human operator. If the systems administrator sees a `.tar.gz` or `.tgz` file extension, for instance, then he knows how to deal with the file.
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The notion of extension under Linux does not exist. In other words, we use extensions here for the human operator. If the systems administrator sees a `.tar.gz` or `.tgz` file extension, for instance, then he knows how to deal with the file.
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### Contents of a backup
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!!! Warning
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Before a restoration, it is important to take time to think about and determine the most appropriate method to avoid mistakes.
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Before a restoration, it is important to consider and determine the most appropriate method to avoid mistakes.
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Restorations are usually performed after a problem has occurred that needs to be resolved quickly. A poor restoration can, in some cases, make the situation worse.
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### Backing up with `tar`
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The default utility for creating backups on UNIX systems is the `tar` command. These backups can be compressed by `bzip2`, `xz`, `lzip`, `lzma`, `lzop`, `gzip`, `compress` or `zstd`.
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`tar` allows you to extract a single file or a directory from a backup, view its contents or validate its integrity.
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`tar` allows you to extract a single file or a directory from a backup, view its contents, or validate its integrity.
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