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Revision as of 11:27, 31 July 2013 by Juma93 (Talk | contribs) (Backup Intervals: Changed "interval" keyword to "retain", as the former one is now deprecated.)

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Summary help replacing me
Instructions on using rsnapshot.

Rsnapshot is an open source utility that provides incremental back ups.


Install the rsnapshot package using pacman:

# pacman -S rsnapshot


In the install process, the config file is created. It is recommended you make a back up of this file in case you need to reconfigure the file again.

# cp /etc/rsnapshot.conf /etc/rsnapshot.conf.default

The rsnapshot.conf config file is well commented, and much of it should be fairly self-explanatory. For a full reference of all the various options, please consult the rsnapshot man page. Type:

# man rsnapshot

Root Directory

Choose the directory where you want to store the file system back ups, in this case I will store the back ups in /mnt/backups/

# All snapshots will be stored under this root directory.
snapshot_root   /mnt/backups/
Note: Fields are separated by tabs, not spaces. The reason for this is so it's easier to specify file paths with spaces in them.

External program dependencies

Uncomment the lines refering to the unix commands cp, du, ssh (if you want to do remote back ups) and rsnapshot-diff, etc. This section of the file should look like this:

# LINUX USERS:   Be sure to uncomment "cmd_cp". This gives you extra features.
# EVERYONE ELSE: Leave "cmd_cp" commented out for compatibility.
# See the README file or the man page for more details.
cmd_cp          /usr/bin/cp

# uncomment this to use the rm program instead of the built-in perl routine.
cmd_rm          /usr/bin/rm

# rsync must be enabled for anything to work. This is the only command that
# must be enabled.
cmd_rsync       /usr/bin/rsync

# Uncomment this to enable remote ssh backups over rsync.
cmd_ssh /usr/bin/ssh

# Comment this out to disable syslog support.
cmd_logger      /usr/bin/logger

# Uncomment this to specify the path to "du" for disk usage checks.
# If you have an older version of "du", you may also want to check the
# "du_args" parameter below.
cmd_du          /usr/bin/du

# Uncomment this to specify the path to rsnapshot-diff.
cmd_rsnapshot_diff      /usr/bin/rsnapshot-diff

# Specify the path to a script (and any optional arguments) to run right
# before rsnapshot syncs files
#cmd_preexec    /path/to/preexec/script

# Specify the path to a script (and any optional arguments) to run right
# after rsnapshot syncs files
#cmd_postexec   /path/to/postexec/script
Note: cmd_preexec and cmd_postexec are custom scripts to be run before and after each run of rsnapshot

Backup Intervals

rsnapshot has no idea how often you want to take snapshots. In order to specify how much data to save, you need to tell rsnapshot which intervals to retain, and how many of each. An interval, wich is specified with the keyword retain, in the context of the rsnapshot config file, is a unit of time measurement. These can actually be named anything (as long as it's alphanumeric, and not a reserved word), but by convention we will call ours hourly and daily. In this example, we want to take a snapshot every four hours, or six times a day (these are the hourly intervals). We also want to keep a second set, which are taken once a day, and stored for a week (or seven days). This happens to be the default, so as you can see the config file reads:

retain    hourly  6
retain    daily   7

Back up

This is the section where you tell rsnapshot what files you actually want to back up. You put a “backup” parameter first, followed by the full path to the directory or network path you're backing up. The third column is the relative path you want to back up to inside the snapshot root.


backup  /home/          localhost/

In this example, backup tells us it's a backup point. /home/ is the full path to the directory we want to take snapshots of, and localhost/ is a directory inside the snapshot_root we're going to put them in. Using the word localhost as the destination directory is just a convention. You might also choose to use the server's fully qualified domain name instead of localhost. If you are taking snapshots of several machines on one dedicated backup server, it's a good idea to use their various hostnames as directories to keep track of which files came from which server.

Remote Systems

In addition to full paths on the local filesystem, you can also backup remote systems using rsync over ssh. If you have ssh installed and enabled (via the cmd_ssh parameter), you can specify a path like:



This behaves fundamentally the same way, but you must take a few extra things into account:

  • The ssh daemon must be running on
  • You must have access to the account you specify the remote machine, in this case the root user on
  • You must have key-based logins enabled for the root user at, without passphrases. If you wanted to perform backups as another user, you could specify the other user instead of root for the source (i.e. Please note that allowing remote logins with no passphrase is a security risk that may or may not be acceptable in your situation. Make sure you guard access to the backup server very carefully! For more information on how to set this up, please consult the ssh man page, or a tutorial on using ssh public and private keys. You will find that the key based logins are better in many ways, not just for rsnapshot but for convenience and security in general. One thing you can do to mitigate the potential damage from a backup server breach is to create alternate users on the client machines with uid and gid set to 0, but with a more restrictive shell such as scponly.
  • This backup occurs over the network, so it may be slower. Since this uses rsync, this is most noticeable during the first backup. Depending on how much your data changes, subsequent backups should go much, much faster since rsync only sends the differences between files.

Extra Scripts

There is an extra backup_script line. With this parameter, the second column is the full path to an executable backup script, and the third column is the local path you want to store it in (just like with the "backup" parameter). For example:

backup_script      /usr/local/bin/       localhost/postgres/

In this example, rsnapshot will run the script /usr/local/bin/ in a temp directory, then sync the results into the localhost/postgres/ directory under the snapshot root.

Your backup script simply needs to dump out the contents of whatever it does into it's current working directory. It can create as many files and/or directories as necessary, but it should not put its files in any pre-determined path. The reason for this is that rsnapshot creates a temp directory, changes to that directory, runs the backup script, and then syncs the contents of the temp directory to the local path you specified in the third column. A typical backup script would be one that archives the contents of a database. It might look like this:

/usr/bin/mysqldump -uroot mydatabase > mydatabase.sql
/bin/chmod 644 mydatabase.sql
Note: Make sure the destination path you specify is unique. The backup script will completely overwrite anything in the destination path, so if you tried to specify the same destination twice, you would be left with only the files from the last script. Fortunately, rsnapshot will try to prevent you from doing this when it reads the config file.
Note: Please remember that these backup scripts will be invoked as the user running rsnapshot. In our example, this is root. Make sure your backup scripts are owned by root, and not writable by anyone else. If you fail to do this, anyone with write access to these backup scripts will be able to put commands in them that will be run as the root user. If they are malicious, they could take over your server.

Testing the configuration

When you have made all your changes, you should verify that the config file is syntactically valid, and that all the supporting programs are where you think they are. To do this, run rsnapshot with the configtest argument:

# rsnapshot configtest

If all is well, it should say Syntax OK. If there's a problem, it should tell you exactly what it is. Make sure your config file is using tabs and not spaces, etc.

The final step to test your configuration is to run rsnapshot in test mode. This will print out a verbose list of the things it will do, without actually doing them. To do a test run, run this command:

# rsnapshot -t hourly

This tells rsnapshot to simulate an "hourly" backup. It should print out the commands it will perform when it runs for real.

Note: Please note that the test output might be slightly different than the real execution, but only because the test doesn't actually do things that may be checked for later in the program. For example, if the program will create a directory and then later test to see if that directory exists, the test run might claim that it would create the directory twice, since it didn't actually get created during the test. This should be the only type of difference you will see while running a test.


Now that you have your config file set up, it's time to set up rsnapshot to be run from cron. As the root user, edit root's crontab by typing:

# crontab -e

You could alternately keep a crontab file that you load in, but the concepts are the same. You want to enter the following information into root's crontab:

Crontab file
0 */4 * * *       /usr/local/bin/rsnapshot hourly
30 23 * * *       /usr/local/bin/rsnapshot daily
Note: It is usually a good idea to schedule the larger intervals to run a bit before the lower ones. For example, in the crontab above, notice that daily runs 30 minutes before hourly. This helps prevent race conditions where the daily would try to run before the hourly job had finished. This same strategy should be extended so that a weekly entry would run before the daily and so on.

How it works

We have a snapshot root under which all backups are stored. In this example, this is the directory /mnt/backups/. Within this directory, other directories are created for the various intervals that have been defined. In the beginning it will be empty, but once rsnapshot has been running for a week, it should look something like this:

[root@localhost]# ls -l /mnt/backups/
drwxr-xr-x    7 root     root         4096 Dec 28 00:00 daily.0
drwxr-xr-x    7 root     root         4096 Dec 27 00:00 daily.1
drwxr-xr-x    7 root     root         4096 Dec 26 00:00 daily.2
drwxr-xr-x    7 root     root         4096 Dec 25 00:00 daily.3
drwxr-xr-x    7 root     root         4096 Dec 24 00:00 daily.4
drwxr-xr-x    7 root     root         4096 Dec 23 00:00 daily.5
drwxr-xr-x    7 root     root         4096 Dec 22 00:00 daily.6
drwxr-xr-x    7 root     root         4096 Dec 29 00:00 hourly.0
drwxr-xr-x    7 root     root         4096 Dec 28 20:00 hourly.1
drwxr-xr-x    7 root     root         4096 Dec 28 16:00 hourly.2
drwxr-xr-x    7 root     root         4096 Dec 28 12:00 hourly.3
drwxr-xr-x    7 root     root         4096 Dec 28 08:00 hourly.4
drwxr-xr-x    7 root     root         4096 Dec 28 04:00 hourly.5

Inside each of these directories is a full backup of that point in time. The destination directory paths you specified under the backup and backup_script parameters get stuck directly under these directories. In the example:

backup          /etc/           localhost/

The /etc/ directory will initially get backed up into /mnt/backups/hourly.0/localhost/etc/

Each subsequent time rsnapshot is run with the hourly command, it will rotate the hourly.X directories, and then copy the contents of the hourly.0 directory (using hard links) into hourly.1.

When rsnapshot daily is run, it will rotate all the daily.X directories, then copy the contents of hourly.5 into daily.0.

hourly.0 will always contain the most recent snapshot, and daily.6 will always contain a snapshot from a week ago. Unless the files change between snapshots, the “full” backups are really just multiple hard links to the same files. Thus, if your /etc/passwd file doesn't change in a week, hourly.0/localhost/etc/passwd and daily.6/localhost/etc/passwd will literally be the same exact file. This is how rsnapshot can be so efficient on space. If the file changes at any point, the next backup will unlink the hard link in hourly.0, and replace it with a brand new file. This will now take double the disk space it did before, but it is still considerably less than it would be to have full unique copies of this file 13 times over.

Remember that if you are using different intervals than the ones in this example, the first interval listed is the one that gets updates directly from the main filesystem. All subsequently listed intervals pull from the previous intervals. For example, if you had weekly, monthly, and yearly intervals defined (in that order), the weekly ones would get updated directly from the filesystem, the monthly ones would get updated from weekly, and the yearly ones would get updated from monthly.