Relax-and-Recover (ReaR) image as container image

Relax-and-Recover (ReaR) image as container image

Relax-and-Recover (ReaR) root file system creation

You know (or don’t know) that with Relax-and-Recover (Rear) program you can keep the root file system generated by rear for debugging purposes. Simple use the -d flag with the rear command and that’s it. At the end of a rear mkrescue or rear mkbackup run you will see a message like:

You should also rm -Rf /tmp/rear.GZnPEjAbYT5mP4Y

That is the temporary workspace of ReaR that you can examine if needed. It is rare that somebody does this, but it is there if you ever need it for deeper investigation of an issue or whatever you want to see in-depth.

Another purpose is to chroot the temporary root file system created by ReaR to see if all required libraries are there and so on. This is now automatically performed by ReaR if you use a recent version of rear (2.5 or higher).

Running the rear2docker.sh script

Well, instead of simple using chroot to inspect or debug the root file system created by ReaR why not creat a container image? Just for the fun of it! Script rear2docker.sh [1] does this for you. Of course, it requires that rear and docker are installed on your system. Just download the script (or git clone the mismas project [2]) and execute it:

$ sudo ./rear2docker.sh 
Running "rear -d mkrescue"
Relax-and-Recover 2.3 / Git
Using log file: /var/log/rear/rear-noc.log
Using backup archive '/tmp/rear.GZnPEjAbYT5mP4Y/outputfs/noc/backup.tar.gz'
Creating disk layout
Using guessed bootloader 'GRUB'
Creating root filesystem layout
To log into the recovery system via ssh set up /root/.ssh/authorized_keys or specify SSH_ROOT_PASSWORD
Copying logfile /var/log/rear/rear-noc.log into initramfs as '/tmp/rear-noc-partial-2021-05-05T17:20:38+02:00.log'
Copying files and directories
Copying binaries and libraries
Copying kernel modules
Copying all files in /lib*/firmware/
Creating recovery/rescue system initramfs/initrd initrd.cgz with gzip default compression
Created initrd.cgz with gzip default compression (251008115 bytes) in 52 seconds
Making ISO image
Wrote ISO image: /var/lib/rear/output/rear-noc.iso (249M)
Copying resulting files to nfs location
Saving /var/log/rear/rear-noc.log as rear-noc.log to nfs location
You should also rm -Rf /tmp/rear.GZnPEjAbYT5mP4Y

	ReaR image created - continue to create a container image

rear-2.3-noc:20210505 with id=sha256:6f9ecfdae914912dfe30bf23ef1724144965c882825ff647128d8959670bca05 created!
To explore run: docker run -it rear-2.3-noc:20210505 /bin/bash

	Entering the container image rear-2.3-noc:20210505
	It behaves the same as "chroot /tmp/rear.GZnPEjAbYT5mP4Y/rootfs"
	Type "exit" to go back to the normal shell.
	Container rear-2.3-noc:20210505 will be removed automatically.


Welcome to Relax-and-Recover. Run "rear recover" to restore your system !

RESCUE 4668d09dc1c5:/ # ls
bin  boot  dev	etc  init  lib	lib64  mnt  proc  root	run  sbin  selinux  sys  tmp  usr  var

After exiting the docker shell the container is automatically removed, but the image is still there:

$ docker images
REPOSITORY     TAG        IMAGE ID       CREATED          SIZE
rear-2.3-noc   20210505   6f9ecfdae914   32 minutes ago   573MB

To remove the container image you need to run docker rmi 6f9ecfdae914 (the IMAGE ID will be different in your environment).

However, when you exited the container image the script continued with the following:

RESCUE 4668d09dc1c5:/ # exit
exit
Press "y" key to chroot $ROOTFS - any other will remove the temporary rear workspace [time-out 5 sec]: 

Welcome to Relax-and-Recover. Run "rear recover" to restore your system !

RESCUE noc:/ # ls
bin  boot  dev	etc  init  lib	lib64  mnt  proc  root	run  sbin  selinux  sys  tmp  usr  var

We have chrooted into the temporary root file system of the ReaR rescue image. As you can see it is exactly the same as we saw in the container image. That makes sense as it is the same root file system. When you exit this chroot environment the temporary workspace of rear will be removed.

RESCUE noc:/ # exit
exit
Removing temporary rear workspace /tmp/rear.GZnPEjAbYT5mP4Y

Happy debugging.

References

[1] Source of rear2docker.sh

[2] mismas github project

Edit History

• Initial posted on 5 May 2021