Arch Linux

theo01

Member

Registered: 2025-01-17

Posts: 5

shrink and move luks encrypted root partition

Hello,

I have a root filesystem encrypted with luks1 and and I need to resize and move it to the right in order to grow my boot partition. How can I proceed ?

# lsblk -f
NAME                                          FSTYPE      FSVER LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINTS
loop0                                         squashfs    4.0                                                    0   100% /var/lib/snapd/snap/core20/2379
loop1                                         squashfs    4.0                                                    0   100% /var/lib/snapd/snap/core20/2434
loop2                                         squashfs    4.0                                                    0   100% /var/lib/snapd/snap/snapd/23258
loop3                                         squashfs    4.0                                                    0   100% /var/lib/snapd/snap/snapd/23545
nvme0n1
├─nvme0n1p1                                   vfat        FAT32       AC41-B686                             133,4M    56% /boot
├─nvme0n1p2                                   crypto_LUKS 1           87550b66-7982-4503-9dec-c23d015351ce
│ └─luks-87550b66-7982-4503-9dec-c23d015351ce ext4        1.0         4604eb05-9aeb-453f-9cd2-6d6e6f30ee9f  663,2G    59% /
└─nvme0n1p3                                   crypto_LUKS 1           1676a75f-b260-453c-890d-75ccaec3292b
  └─luks-1676a75f-b260-453c-890d-75ccaec3292b swap        1     swap  d463e634-4e5a-4ca3-9de7-297df5e0ac08                [SWAP]

# cryptsetup status /dev/mapper/luks-87550b66-7982-4503-9dec-c23d015351ce
/dev/mapper/luks-87550b66-7982-4503-9dec-c23d015351ce is active and is in use.
  type:    LUKS1
  cipher:  aes-xts-plain64
  keysize: 512 bits
  key location: dm-crypt
  device:  /dev/nvme0n1p2
  sector size:  512
  offset:  4096 sectors
  size:    3928465583 sectors
  mode:    read/write
  flags:   discards

frostschutz

Member

Registered: 2013-11-15

Posts: 1,487

Re: shrink and move luks encrypted root partition

I would leave the partition where it is and instead relocate /boot to the end of disk. It's not necessary to shuffle around 600+GB of data, risking data loss in the process.

Otherwise do a full backup and then just set it up from scratch. Probably faster to copy files anyways (since that filesystem is 50% empty).

theo01

Member

Registered: 2025-01-17

Posts: 5

Re: shrink and move luks encrypted root partition

True, moving /boot to then end of disk sounds safer than moving data around. Yet I have no free space at the end of disk. What tool should I use ? resize2fs and cryptsetup resize ? I just don't know what's the sequence there.

gcb

Member

Registered: 2014-02-12

Posts: 183

Re: shrink and move luks encrypted root partition

another option is not needing a larger boot.

I use 1GB for boot and never care about that. but sometimes i get employer machines with those small /boot and have to set it up for 1) compress initramfs https://wiki.archlinux.org/title/Mkinitcpio#COMPRESSION and 2) remove fallback and other things https://bbs.archlinux.org/viewtopic.php … 5#p2154175

kermit63

Member

Registered: 2018-07-04

Posts: 288

Re: shrink and move luks encrypted root partition

How big is your swap partition?

If it is big enough, you may be able to skim off a few hundred MBs from it to create a /boot partition at the end of the disk, as frostschutz suggested. It is a lot easier resizing or even recreating the swap partition.

Another option is to totally do away with the swap partition, then create a swap file in your root partition to take its place. This should free up more than enough space at the end of the disk.

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A journey of a thousand miles begins with a single step.

theo01

Member

Registered: 2025-01-17

Posts: 5

Re: shrink and move luks encrypted root partition

I workaround this by changing the initramfs compression to default: zstd, so I can now fit 2 initramfs in boot but this solution won't last long as there's now only 20Mb left on the boot partition. For now I am good.
My swap partition is 34Gb.
If I need more space I'll consider either removing the fallback images or moving my boot partition to end of disk after swap. Thanks for your help.