swapoff failed: Invalid argument

Question

I recently found that every time I shutdown/reboot my machine, there will be an logged error which says swapoff failed: Invalid argument.

Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopping Update UTMP about System Boot/Shutdown...
Jul 22 21:09:02 Frederick-Kubuntu swapoff[5049]: swapoff: /dev/disk/by-uuid/cc08e210-8609-4cf8-9b7c-6af95b0c38eb: swapoff failed: Invalid argument
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopped target Remote File Systems.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopped target Remote File Systems (Pre).
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopped target User and Group Name Lookups.
Jul 22 21:09:02 Frederick-Kubuntu systemd[5049]: dev-disk-by\x2duuid-cc08e210\x2d8609\x2d4cf8\x2d9b7c\x2d6af95b0c38eb.swap: Executing: /sbin/swapoff /dev/disk/by-uuid/cc08e210-8609-4cf8-9b7c-6af95b0c38eb
Jul 22 21:09:02 Frederick-Kubuntu systemd[5048]: dev-nvme0n1p9.swap: Executing: /sbin/swapoff /dev/nvme0n1p9
Jul 22 21:09:02 Frederick-Kubuntu systemd[5051]: systemd-update-utmp.service: Executing: /lib/systemd/systemd-update-utmp shutdown
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopped Load/Save Random Seed.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopped Load/Save Screen Backlight Brightness of backlight:acpi_video0.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: dev-disk-by\x2duuid-cc08e210\x2d8609\x2d4cf8\x2d9b7c\x2d6af95b0c38eb.swap: Swap process exited, code=exited status=255
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Deactivated swap /dev/disk/by-uuid/cc08e210-8609-4cf8-9b7c-6af95b0c38eb.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: dev-disk-by\x2duuid-cc08e210\x2d8609\x2d4cf8\x2d9b7c\x2d6af95b0c38eb.swap: Unit entered failed state.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Deactivated swap /dev/disk/by-partuuid/3c715e0f-205c-4138-9249-127984925f66.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Deactivated swap /dev/disk/by-partlabel/Linux\x20Swap.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Deactivated swap Swap Partition.
Jul 22 21:09:02 Frederick-Kubuntu systemd[1]: Stopped Update UTMP about System Boot/Shutdown.

I tried to execute the command manually and nothing wrong was found.

frederick@Frederick-Kubuntu:~$ sudo blkid /dev/nvme0n1p9 # this is the swap part
/dev/nvme0n1p9: UUID="cc08e210-8609-4cf8-9b7c-6af95b0c38eb" TYPE="swap" PARTLABEL="Linux Swap" PARTUUID="3c715e0f-205c-4138-9249-127984925f66"
frederick@Frederick-Kubuntu:~$ free -m
            total        used        free      shared  buff/cache   available
Mem:          16000        1828       12462          88        1709       13734
Swap:          7629           0        7629
frederick@Frederick-Kubuntu:~$ sudo /sbin/swapoff /dev/disk/by-uuid/cc08e210-8609-4cf8-9b7c-6af95b0c38eb
frederick@Frederick-Kubuntu:~$ free -m
            total        used        free      shared  buff/cache   available
Mem:          16000        1826       12466          88        1708       13736
Swap:             0           0           0
frederick@Frederick-Kubuntu:~$ sudo /sbin/swapon /dev/disk/by-uuid/cc08e210-8609-4cf8-9b7c-6af95b0c38eb
frederick@Frederick-Kubuntu:~$ free -m
            total        used        free      shared  buff/cache   available
Mem:          16000        1828       12463          88        1708       13734
Swap:          7629           0        7629

I tried to use mkswap to rebuild the swap partition but it didn't work (I specified UUID so /etc/fstab is still correct).

How can I suppress this error? Thanks in advance.

Solution

swapoff tells you swapoff failed: Invalid argument when the device is already not being used for swap. Example:

deltik@node51 [~]$ sudo swapoff /dev/zero
swapoff: /dev/zero: swapoff failed: Invalid argument

This is not an error. It just means that the device isn't being used as swap at the time you shut down your computer.

If you're wondering why systemd even tries to swapoff, it's by design (emphasis mine):

Before shutting down, this binary will try to unmount all remaining file systems, disable all remaining swap devices, detach all remaining storage devices and kill all remaining processes.

Comments

[Frederick Zhang]

Wow, excellent answer. I was exactly wondering why there were several tries to disable the swap.