For some reason I can't really explain, I woke up the other day with this urgent need to change of Linux distribution.
I have been a long time user of debian or debian-derived distribution.
My laptop has been running Ubuntu since at least 2011.
I didn't know Arch Linux until a few weeks ago.
I read an article about it online, and it took some time before I made up my mind.
After a few days of transition, my laptop is now running Arch Linux.
I felt like sharing the process I went thru, in the event someone would find it useful.
Initial setting: Ubuntu 20.04 LTS, up to date as of september 15th.
Boot and disk settings are critical for such a transition.
So the boot setting was BIOS/MBR. grub2 was installed on /dev/sda The kernel, initrd and settings were stored on /dev/sda1 which is ext2 formatted.
Disk setting: The system was configured with full disk encryption (LUKS) + home directory encryption. To be more specific:
fdisk -l /dev/sda gives this: Device Boot Start End Sectors Size Id Type /dev/sda1 * 2048 499711 497664 243M 83 Linux /dev/sda2 499712 1000214527 999714816 476.7G 5 Extended /dev/sda5 501760 1000214527 999712768 476.7G 83 Linux
/dev/sda1 is unencrypted and ext2 formatted. By the way: 240MB is too small for a /boot partition: I keep running into "No space available on device" when upgrading my system, while I only have 2 or 3 kernels and corresponding initrd installed...
Let's have a look at the LVM configuration:
pvs PV VG Fmt Attr PSize PFree /dev/mapper/sda5_crypt erika-vg lvm2 a-- <476.70g 0 vgs VG #PV #LV #SN Attr VSize VFree erika-vg 1 3 0 wz--n- <476.70g 0 lvs LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert root erika-vg -wi-a----- 476.70g swap_1 erika-vg -wi-a----- 9.00g
Moreover, ecryptfs is installed, and /home/.ecrypt/florian/.Private is mounted on /home/florian when I log in.
Statement of my objective: I want to have my laptop transition to Arch Linux without loosing all my documents. I don't want to do a full backup, wipe the system, install Arch and then restore my files. I find some interesting challenge in the idea of making the transition between the 2 distributions. In the process, I want to get rid of ecryptfs home directory (which is redundant with full disk encryption anyway since I am the only user of the laptop): this will not be described here. You can follow some tutorials to get rid of ecryptfs.
Process I went thru: The arch linux (https://wiki.archlinux.org/index.php/installation_guide) is very detailed, but doesn't cover the transition as I wanted to do it.
Obviously, you need to make up some space to install Arch, while keeping Ubuntu.
I used the tecmint tutorial (https://www.tecmint.com/extend-and-reduce-lvms-in-linux/) about resizing LVM volumes. It is very clear. It requires to boot the system from USB because resizing of a mounted filesystem is not recommanded. Therefore, I made a USB key with a live Arch Linux system following the instructions from the ArchWiki (https://wiki.archlinux.org/index.php/USB_flash_installation_medium)
Once Arch Linux is booted from USB, you need to access the encrypted LVM volumes:
cryptsetup luksOpen /dev/sda5 sda5_crypt
Then udev does its magic and the volumes are available in /dev/mapper.
If not,
vgchange -ay
Then I reduced the size of the root volume by 100G. Once the root volume is resized, you can reboot to Ubuntu and create a new volume for arch linux:
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert arch-root erika-vg -wi-ao---- <166.70g root erika-vg -wi-a----- 301.00g swap_1 erika-vg -wi-a----- 9.00g
Note: this procedure implies that Arch Linux will reside in a fully encrypted (LUKS) LVM logical volume. If you want to have arch linux unencrypted, you need to reduce the root volume, then reduce the sda5 partition and create a new partition which will become your new unencrypted root.
Then, one can follow the ArchWiki installation guide (https://wiki.archlinux.org/index.php/installation_guide): - format this new volume (I chose ext4) - use pacstrap to deploy the base arch system - use arch-chroot to setup essential system parameters (notably the root password...)
Because we want the existing grub to boot the newly installed arch system.
Once your are there, you can update grub so that it becomes arch-aware. grub-mkconfig will do the trick, and should both detect the ArchLinux kernel and initrd, and the fact that Arch Linux is available on the new LVM volume. However, you will have to check the grub.cfg entries. On my system, despite showing the appropriate labels, the grub entries for Arch Linux didn't point the kernel towards the right root device.
Once you are here, you can boot both Ubuntu and Arch Linux from Grub. The most difficult part is over.
You can now configure the new system easily, since you can always reboot to Ubuntu.
This is the last critical step. Until now, GRUB is the grub that was installed from Ubuntu. In order for your transition to Arch to be complete, you will want to reinstall Grub from Arch to /dev/sda, making sure that you can still dual-boot to ubuntu.
For example your documents or any other file that you might want to keep.
Conclusion: It has been 15 days now that I am using Arch as my primary system. I haven't gone thru step 8 yet, because I don't want to rush and regret. But so far, everything is going well, and I am very pleased to have been able to transition from Ubuntu to Arch as explained here. Arch Linux installation is commonly considered as a challenge. Arch linux installation over an existing full disk encrypted system adds some complexity but is achievable if you use method and good thinking.