Warning message about cryptsetup during boot

I have noticed that since upgrade to 20.04.1 (from 18.04), a warning message appears during boot: "cryptsetup: WARNING: Option 'size' missing in crypttab for plain dm-crypt mapping cryptswap1. Please read /usr/share/doc/cryptsetup-initramfs/README.initramfs.gz and add the correct 'size' option to your crypttab(5).".

AFAICT, there is no problem however. I use ecryptfs to encrypt my home directory but I don't think it's related (since the message is related to swap). This message used to appear during updates under 18.04 but I never paid attention to it. I probably use the same setup since 16.04.

Others have reported the problem (https://askubuntu.com/questions/1109463, https://medium.com/@anirudha/fixing-cryptsetup-wating-for-encrypted-source-device-swapfile-error-on-linux-boot-ubuntu-20-04-5483e0dcf9e9). From what I read:

  - The answers indicate to edit /etc/crypttab and add a value for size but I don't know what value to use.
  - It seems that before 20.04, just editing /etc/crypttab was enough but some users say that they need to manually regenerate the initramfs image after each update which is boring.

I have asked the question at https://answers.launchpad.net/ubuntu/+question/693615 and @bernard010 suggested to open a bug report.

I have found anything worth in dmesg though.

As I said everything seems fine (boot proceeds normally, I can use the computer) but I expect that there is a way to permanently make this warning disappear.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: linux-image-5.4.0-53-generic 5.4.0-53.59
ProcVersionSignature: Ubuntu 5.4.0-53.59-generic 5.4.65
Uname: Linux 5.4.0-53-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.11
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: mathieu 2322 F.... pulseaudio
CasperMD5CheckResult: skip
CurrentDesktop: ubuntu:GNOME
Date: Wed Nov 11 23:02:47 2020
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-01-06 (1405 days ago)
InstallationMedia: Ubuntu 16.04.1 LTS "Xenial Xerus" - Release amd64 (20160719)
MachineType: Hewlett-Packard HP EliteBook 2570p
ProcFB: 0 i915drmfb
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-5.4.0-53-generic root=UUID=74d77edf-b4b7-4815-865f-b7602f3396b4 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 linux-restricted-modules-5.4.0-53-generic N/A
 linux-backports-modules-5.4.0-53-generic N/A
 linux-firmware 1.187.4
SourcePackage: linux
UpgradeStatus: Upgraded to focal on 2020-10-04 (38 days ago)
dmi.bios.date: 02/01/2013
dmi.bios.vendor: Hewlett-Packard
dmi.bios.version: 68ISB Ver. F.40
dmi.board.name: 17DF
dmi.board.vendor: Hewlett-Packard
dmi.board.version: KBC Version 61.21
dmi.chassis.asset.tag: CNU3229ST9
dmi.chassis.type: 10
dmi.chassis.vendor: Hewlett-Packard
dmi.modalias: dmi:bvnHewlett-Packard:bvr68ISBVer.F.40:bd02/01/2013:svnHewlett-Packard:pnHPEliteBook2570p:pvrA1029C1102:rvnHewlett-Packard:rn17DF:rvrKBCVersion61.21:cvnHewlett-Packard:ct10:cvr:
dmi.product.family: 103C_5336AN G=N L=BUS B=HP S=ELI
dmi.product.name: HP EliteBook 2570p
dmi.product.sku: C9S65EC#ABF
dmi.product.version: A1029C1102
dmi.sys.vendor: Hewlett-Packard