Resize LVM on LUKS partition without messing everything up

Since forever I run my work computer operating systems on a full-disk-encrypted partition. Currently this is Manjaro Linux. When I set up my current machine I made the following partition scheme:

sda                  238,5G  disk
├─sda1                 260M  part  /boot/efi
├─sda2                 128M  part  /boot
└─sda3                 237G  part
  └─tank               237G  crypt

Somewhere, I can't even remember when, I read that 128M for /boot would be sufficient. And it was for a few years. But kernel images and/or initram disks grew bigger and bigger until I could not upgrade to a newer kernel anymore. The last kernel I ran was Linux 4.16 and the files in /boot took around 75M space and so mhwd-kernel -i linux417 had too little space on the device left.

What I needed to do was to shrink /dev/sda3, move it to the end of the SSD and grow /dev/sda2 as necessary.

But I did not know if this was even possible with my setup. Inside the encrypted partition there is an LVM container with 5 logical volumes including /. I pushed it into the future again and again because most of the time I am working in running projects and can not afford to have a non-functioning machine for <absurd amount of time that you never expect before a hardware near change>.

But in the end it was relatively easy. I had feared that in the worst case I would have to re-setup my whole machine and restore backups for the data and system partitions. Which then maybe would need endless tweaking until it runs again (No, I never had a hard disk failure or similar, so I never had to actually do anything like that).

So, here are the things I needed to do:

1. Backup

List all logcal volumes:

# lvs
LV     VG   Attr       LSize   Pool Origin Data%  Meta%  Move Log Cpy%Sync Convert
docker tank -wi-ao----   5,00g                                        
home   tank -wi-ao---- 100,00g                                        
mongo  tank -wi-ao----   1,00g                                        
root   tank -wi-ao----  25,00g                                        
swap   tank -wc-ao----  32,00g

For each lv do the following:

# lvcreate -s -n <name>snap /dev/tank/<name>
# dd if=/dev/tank/<name>snap of=/path/to/external/storage/<name>.img

Where <name> must be replaced by the actual names of the lvs. Then I backed up both the /boot and the /boot/efi partitions, also with dd.
Finally I made a backup of the LUKS header for the crypto-partition:

# cryptsetup luksHeaderBackup /dev/sda3 --header-backup-file /path/to/external/storage/luks-header.bkp

2. Boot in a live system from an USB stick and decrypt the device

# cryptsetup open /dev/sda3 tank --type luks 

3. Resize the physical volume

Note: I have free space inside my LVM container. As you can see from the output of lvs above I currently use only 143GB out of roughly 238GB. That means I do not have to resize logical volumes before I resize the containing physical volume. If you use all of the available space for logical volumes, look into lvresize(8) first: For example in the Arch Wiki.

I generously shrank the volume from 238,07G to 236G with:

# pvresize --setphysicalvolumesize 236G /dev/mapper/tank

4. Resize the crypto-device

Find out how many sectors is the current size (note that my crypto-device has the same name like my volume group: tank. That could be different in your setup):

# cryptsetup status tank
...
sector size:  512
size:  499122176
...

In the end I want to add about 1G to the /boot partition. That is 1024 * 1024 * 1024 / 512 = 2097152 sectors.

# cryptsetup -b 497025024 resize tank

5. Resize the GUID partition

You see we go from innermost to outermost: LVM -> crypto -> GUID. I use parted to resize the partition /dev/sda3:

# parted
(parted) unit s
(parted) print
...
Number  Begin     End         Size                     Name  Flags
...
3      3100672s  500115455s  497014784s               TANK  lvm

These numbers were actually different as I write this blog post in hindsight. The point is that partition number 3 went all the way to the last sector of the disk and I now must calculate where it should end in the future. Because resizepart takes not the future size but the future end sector of the partition as argument. So I subtract the same sector count as calculated above for cryptsetup (2097152) from the end sector of partition 3 (500115455) which gives 498018303.

(parted) resizepart 3 498018303s

Now we have free space on the SSD after the main partition. But I want to grow partition 2.

6. Reorder partitions and resize partition 2

I did that with GParted instead of a command line tool. Probably there is a way to do it with gdisk but parted has removed its command to move partitions. And because I was in a graphical live system anyway and also read that you could do it with GParted I just went for it.
First I closed the crypto device because GParted would not let me move the partition otherwise:

# vgchange -an tank
# cryptsetup close tank

Then I opened GParted and right-clicked on the crypto partition. I chose "Change size|Move" and moved the free space after the partition before it. Then I opend the same dialog for the /boot partition and extended it to cover all of the free space. Finally I committed the changes.