Backing up in Linux using tar, gzip an rsync
About TAR and GZIP
Linux has combined the following programs:
TAR
GZIP
The “tar” utility archives but doesn’t compress very well,so we use the “gzip” along with “tar” to compress.
Zipping
The command to zip and compress is “tar -vzcf”
The command to zip only is “tar -vcf”
Exercise:
Back up the /etc directory as follows;
“tar -vcf etc.tar /etc”
Have a look at the size.Now back up using GZIP with TAR as follows;
“tar -vzcf etc.tar.gz /etc” (v=verbose; z=gzip; c=create; f=file) notice the difference in size
Extracting
The command to restore a zipped and compressed file is “tar -vzxf zipfile.tar.gz” The command to restore a zipped only file is
“tar -vxf zipfile.tar.gz”
To extract to a different location you would include the “-C” switch followed by the location, as follows:
tar -vzxf home.tar.gz -C /home/extracted/
To extract selected files use the “tar -vzxf zipfile.tar.gz location/filetoextract.txt” command.
Viewing the content of a tar.gz file
You can view the content of a zipped file with the following command (In this example I have piped the output to “more”)
tar -tzvf /backup/etc.tar.zg | more
How to do an incremental backup:
For an incremental backup, tar needs to generate a file which tells tar which files have been backed up and when. To generate this file you need to use the “-g” switch as follows:
First you need to do a full backup which will generate the “snapshot_file” if it doesn”t exist
tar -cz -g /backup/snapshot_file -f /backup/backup_monday.tar.gz /home
Next you need to do the incremental backup, making use of the “snapshot_file” file
tar -cz -g /backup/snapshot_file -f /backup/backup_tuesday.tar.gz /home
Mirroring directories with the “rsync” command:
The rsync command makes a mirror image of the directory you select. You can mirror to a local folder, or a folder on a remote computer.
Using rsync to mirror locally:
rsync -a /home /mirror
if you wanted to mirror the contents of the home directory, including it”s file structure, but not the home directory its self, type the following:
rsync -a /home/. /mirror
When you run the command again, only files that have changed will be updated
Here are some of the switches you can use:
-a Archive mode
-x Does not follow links etc to other locations
-v Verbose mode
-z Compresses during transfer (suited for remote transfer)
–delete Deletes files on the mirror that no longer exist in the original directory
–exclude-from Does not backup files included in the exclude file
Use the “exclude” option as follows:
rsync -a -exclude-from /home/exclude /home/. /mirror
Using rsync to mirror to a remote location:
You will need “rsync” installed on both the local and remote computers
Example 1
rsync -ave ssh root@remotepc:/data/. /databackup/
This example copies the files from a remote computer to the local computer into a folder called “databackup”
Example 2
rsync -ave ssh /databackup/ root@remotepc:/data/
This example restores the data from the “databackup” folder on the local folder to the remote computer
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