[Bug 2111762] [NEW] BTRFS swap not reliably mounted when using keyfile with encrypted Kubuntu

Mon May 26 23:10:27 UTC 2025

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If I install either Kubuntu 24.04.2 or 25.04 with a swapfile & BTRFS on
an encrypted (cryptsetup) partition, and add a keyfile, then usually
(but not always) the /swap subvolume fails to mount, such that
/swap/swapfile doesn't exist, and so "cat /proc/swap" lists nothing.
This occurs on two very different laptops & a desktop PC.

After installing Kubuntu, I perform these very minor changes:
$ sudo cryptsetup luksAddKey /dev/sda3 /media/chris/USB/test.key
$ sudo vim /etc/crypttab
$ sudo update-initramfs -u #-k all

Here is my slightly modified /etc/crypttab:
~~~
#luks-09135e69-3422-4c29-b2a2-691197225802 UUID=09135e69-3422-4c29-b2a2-691197225802     none
luks-09135e69-3422-4c29-b2a2-691197225802 UUID=09135e69-3422-4c29-b2a2-691197225802	/dev/disk/by-label/USB:/test.key	keyscript=passdev
~~~

For reference, these are the relevant (but UNchanged) entries in /etc/fstab:
~~~
/dev/mapper/luks-09135e69-3422-4c29-b2a2-691197225802 /swap          btrfs   subvol=/@swap,defaults 0 0
/swap/swapfile                            swap           swap    defaults   0 0
~~~

But I've also seen similar behaviour if I add a bind mount inside the
/home subvolume, so it's not swap specific.  Instead I suspect it's
because cryptsetup is not ready when it tries to mount the /swap
subvolume, as I see the following in the journal:

~~~
chris at chris-test:~$ journalctl -b -g "cryptsetup|luks|swap|local-fs.target|home.mount"
May 26 22:37:42 chris-test kernel: Command line: BOOT_IMAGE=/vmlinuz-6.14.0-15-generic root=UUID=69898faf-5ddc-425a-9e2f-e4798fa1426e ro rootflags=subvol=@ quiet rd.luks.uuid=09135e69-3422-4c29-b2a2-691197225802 splash vt.handoff=7
May 26 22:37:42 chris-test kernel: Kernel command line: BOOT_IMAGE=/vmlinuz-6.14.0-15-generic root=UUID=69898faf-5ddc-425a-9e2f-e4798fa1426e ro rootflags=subvol=@ quiet rd.luks.uuid=09135e69-3422-4c29-b2a2-691197225802 splash vt.handoff=7
May 26 22:37:42 chris-test kernel: Spectre V1 : Mitigation: usercopy/swapgs barriers and __user pointer sanitization
May 26 22:37:43 chris-test kernel: BTRFS: device label kubuntu_2504 devid 1 transid 140 /dev/mapper/luks-09135e69-3422-4c29-b2a2-691197225802 (252:0) scanned by mount (314)
May 26 22:37:43 chris-test systemd[1]: systemd 257.4-1ubuntu3 running in system mode (+PAM +AUDIT +SELINUX +APPARMOR +IMA +IPE +SMACK +SECCOMP +GCRYPT -GNUTLS +OPENSSL +ACL +BLKID +CURL +ELFUTILS +FIDO2 +IDN2 -IDN +IPTC +KMOD +LIBCRYPTSETUP +LIBCRYPTSETUP_PLUGINS +LIBFDISK +PCRE2 +PWQUALITY +P11KIT +QRENCODE +TPM2 +BZIP2 +LZ4 +XZ +ZLIB +ZSTD +BPF_FRAMEWORK +BTF -XKBCOMMON -UTMP +SYSVINIT +LIBARCHIVE)
May 26 22:37:43 chris-test systemd[1]: Created slice system-systemd\x2dcryptsetup.slice - Encrypted Volume Units Service Slice.
May 26 22:37:43 chris-test systemd[1]: Expecting device dev-mapper-luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.device - /dev/mapper/luks-09135e69-3422-4c29-b2a2-691197225802...
May 26 22:37:43 chris-test systemd[1]: Mounting run-systemd-cryptsetup-keydev\x2dluks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.mount - /run/systemd/cryptsetup/keydev-luks-09135e69-3422-4c29-b2a2-691197225802...
May 26 22:37:47 chris-test mount[384]: mount: /run/systemd/cryptsetup/keydev-luks-09135e69-3422-4c29-b2a2-691197225802: special device /test.key does not exist.
May 26 22:37:47 chris-test umount[438]: umount: /run/systemd/cryptsetup/keydev-luks-09135e69-3422-4c29-b2a2-691197225802: not mounted.
May 26 22:37:43 chris-test systemd[1]: run-systemd-cryptsetup-keydev\x2dluks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.mount: Mount process exited, code=exited, status=32/n/a
May 26 22:37:43 chris-test systemd[1]: run-systemd-cryptsetup-keydev\x2dluks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.mount: Failed with result 'exit-code'.
May 26 22:37:43 chris-test systemd[1]: Failed to mount run-systemd-cryptsetup-keydev\x2dluks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.mount - /run/systemd/cryptsetup/keydev-luks-09135e69-3422-4c29-b2a2-691197225802.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for systemd-cryptsetup at luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.service - Cryptography Setup for luks-09135e69-3422-4c29-b2a2-691197225802.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for cryptsetup.target - Local Encrypted Volumes.
May 26 22:37:43 chris-test systemd[1]: cryptsetup.target: Job cryptsetup.target/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for dev-mapper-luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.device - /dev/mapper/luks-09135e69-3422-4c29-b2a2-691197225802.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for swap.mount - /swap.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for swap-swapfile.swap - /swap/swapfile.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for swap.target - Swaps.
May 26 22:37:43 chris-test systemd[1]: swap.target: Job swap.target/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: swap-swapfile.swap: Job swap-swapfile.swap/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for local-fs.target - Local File Systems.
May 26 22:37:43 chris-test systemd[1]: local-fs.target: Job local-fs.target/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: local-fs.target: Triggering OnFailure= dependencies.
May 26 22:37:43 chris-test systemd[1]: swap.mount: Job swap.mount/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: Dependency failed for home.mount - /home.
May 26 22:37:43 chris-test systemd[1]: home.mount: Job home.mount/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: dev-mapper-luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.device: Job dev-mapper-luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.device/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: systemd-cryptsetup at luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.service: Job systemd-cryptsetup at luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.service/start failed with result 'dependency'.
May 26 22:37:43 chris-test systemd[1]: Reached target blockdev at dev-mapper-luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.target - Block Device Preparation for /dev/mapper/luks-09135e69-3422-4c29-b2a2-691197225802.
May 26 22:37:43 chris-test systemd[1]: Started keydev-luks-09135e69-3422-4c29-b2a2-691197225802-umount.service.
May 26 22:37:43 chris-test systemd[1]: Stopped target blockdev at dev-mapper-luks\x2d09135e69\x2d3422\x2d4c29\x2db2a2\x2d691197225802.target - Block Device Preparation for /dev/mapper/luks-09135e69-3422-4c29-b2a2-691197225802.
May 26 22:37:43 chris-test systemd[1]: keydev-luks-09135e69-3422-4c29-b2a2-691197225802-umount.service: Deactivated successfully.
May 26 22:37:55 chris-test systemd[1]: Mounting home.mount - /home...
May 26 22:37:55 chris-test systemd[1]: Mounted home.mount - /home.
~~~

And after booting I can enable swap with "sudo mount /swap" followed by
"sudo swapon --all".  I've tried working-around this bug myself, but the
problem remains no matter what changes I make to /etc/fstab or
/etc/crypttab - although I'm no expert, so perhaps there is some easy
fix that I've overlooked.

NOTE: Once crypttab uses keyscript=passdev, Kubuntu typically offers
"emergency mode" (presumably due to the above failures) - but as long as
I don't touch it, then it usually finishes booting normally, leaving me
at the Plasma desktop.  However if I touch "emergency mode" at all (even
ctrl-D), then usually the swap is working (I presume it retries
something & finds it's able to mount /swap).

** Affects: cryptsetup (Ubuntu)
     Importance: Undecided
         Status: New

-- 
BTRFS swap not reliably mounted when using keyfile with encrypted Kubuntu
https://bugs.launchpad.net/bugs/2111762
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