Chapter 15. Recovering and restoring a system

Use the following steps to install the package for using the Relax-and-Recover (ReaR) utility, create a rescue system, configure and generate a backup.

The /etc/cron.d/rear crontab file in the rear package runs the rear mkrescue command automatically at 1:30 AM everyday to schedule the Relax-and-Recover (ReaR) utility for regularly creating a rescue system. The command only creates a rescue system and not the backup of the data. You still need to schedule a periodic backup of data by yourself. For example:

Basic Relax and Recover (ReaR) functionality is now available on the 64-bit IBM Z architecture and is fully supported since RHEL 8.8. You can create a ReaR rescue image on IBM Z only in the z/VM environment. Backing up and recovering logical partitions (LPARs) has not been tested.

The only output method currently available is Initial Program Load (IPL). IPL produces a kernel and an initial RAM disk (initrd) that can be used with the zIPL boot loader.

The ReaR utility recreates the storage layout of the original system, where the rescue image has been produced, on the disks of the recovered system according to the description in the /var/lib/rear/layout/disklayout.conf layout file during the recovery process. The storage layout includes partitions, volume groups, logical volumes, file systems, and other storage components.

ReaR creates the layout file when creating the rescue image and embeds this file in the image. You can also create the layout file by using the rear savelayout command. This allows you to quickly create the layout file and examine it, without creating the entire rescue image.

The layout file describes the entire storage layout of the original system with certain exceptions, as ReaR excludes some storage components from the layout file and from being recreated during recovery. The exclusion of storage components from layout is controlled by the following configuration variables:

You can view the default values for the configuration variables in the /usr/share/rear/conf/default.conf file and can change these values in the local /etc/rear/local.conf configuration file.

For more information about the syntax of the layout file and the configuration variables that you can use to exclude some storage components, see the Layout configuration chapter in the ReaR user guide, which is installed with the ReaR package as /usr/share/doc/rear/relax-and-recover-user-guide.html.

You can also configure which files are backed up by the internal NETFS and RSYNC backup methods. By default, files on all mounted local (disk-based) file systems are backed up by the rear mkbackup or rear mkbackuponly commands, if the file systems are included in the layout file. Excluding some file systems from the layout file, which is controlled by variables such as AUTOEXCLUDE_DISKS, AUTOEXCLUDE_MULTIPATH, AUTOEXCLUDE_PATH, and EXCLUDE_RECREATE, also excludes their content from the backup. You can also exclude some files or a directory tree from the backup without excluding a file system from the layout file by using the BACKUP_PROG_EXCLUDE configuration variable. When all files and directories in a file system are excluded in this way, the file system is recreated during recovery, but it will be empty, because the backup does not contain any data to restore into it. This is useful for file systems that contain temporary data and are not required to be preserved, or for data that is backed up by using methods independent of ReaR.

The BACKUP_PROG_EXCLUDE variable is an array of glob(3)-style wildcard patterns that are passed to tar or rsync. Note that the patterns are required to be quoted in order to prevent their expansion by the shell when it reads the configuration file. The default value of this variable is set in the /usr/share/rear/conf/default.conf file. The default value contains, for example, the /tmp/* pattern that excludes all the files and directories under the /tmp directory, but not the /tmp directory itself.

If you need to exclude other files and directories, append further patterns to the variable instead of overriding it in order to preserve the default values. For example, to exclude all files and directories under the directory /data/temp, use:

BACKUP_PROG_EXCLUDE+=( '/data/temp/*' )

# BACKUP_PROG_EXCLUDE+=( '/data/temp/*' )

The rear mkbackup command lists the backup exclude patterns in the log. You can find the log file in the /var/log/rear directory. This can be used to verify the excluded rules before performing a full system recovery. For example, the log can contain the following entries:

2025-04-29 10:17:41.312431050 Making backup (using backup method NETFS)
2025-04-29 10:17:41.314369109 Backup include list (backup-include.txt contents):
2025-04-29 10:17:41.316197323   /
2025-04-29 10:17:41.318052001 Backup exclude list (backup-exclude.txt contents):
2025-04-29 10:17:41.319857125   /tmp/*
2025-04-29 10:17:41.321644442   /dev/shm/*
2025-04-29 10:17:41.323436363   /var/lib/rear/output/*

2025-04-29 10:17:41.312431050 Making backup (using backup method NETFS)
2025-04-29 10:17:41.314369109 Backup include list (backup-include.txt contents):
2025-04-29 10:17:41.316197323   /
2025-04-29 10:17:41.318052001 Backup exclude list (backup-exclude.txt contents):
2025-04-29 10:17:41.319857125   /tmp/*
2025-04-29 10:17:41.321644442   /dev/shm/*
2025-04-29 10:17:41.323436363   /var/lib/rear/output/*

Here, the whole root file system is included in the backup, with the exception of all files and directories under the /tmp, /dev/shm and /var/lib/rear/output directories.