Wednesday, 8 May 2019

Linux: Backup Options

There are countless ways to backup disks easily with Linux - however I'm going to demonstrate some of the more commonly used methods.

Forenote: Always ensure the discs are not in use / mounted while performing the below operations otherwise it is likely that new / changed files will be corrupted and will run into problems with the file system.

Backing up a disk with dd 

sudo dd if=/dev/xvda of=/mnt/usbdrive | sync

or better yet we can use a sane block size (dd uses 512 bytes by default):

sudo dd bs=16M if=/dev/xvda of=/mnt/usbdrive | sync

Backing up a disk with dd over ssh

Utilising SSH provides us with encryption - ideal for remote backups e.g. over public networks:

sudo ssh user@remote "dd if=/dev/xvda1 " | dd of=backup.gz

However it does introduce an overhead due to the encryption - so we can pipe it into gzip in order to speed things up:

sudo ssh user@remote "dd if=/dev/xvda1 | gzip -1 -" | dd of=backup.gz

Backing up a mounted system with rsync

If the system is currently mounted we can use rsync to perform a backup (ensuring we exclude certain directories such as /dev, /mnt etc):

sudo rsync -aAXv / --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"} /mnt

In the above command we employ 'archive' mode that ensures symbolic links, devices, permissions, ownerships, modification times, ACLs, and extended attributes are preserved.

and over rsync over SSH

sudo rsync -aAXve ssh user@remote:/ --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"} /mnt

There are of course many other ways to skin a cat e.g. using netcat (which is significantly faster than dd over SSH - however lacks encryption.) 



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