BTRFS Swap "Not enough swap space for hibernation"

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1

systemctl hibernate says Not enough swap space, but free -h indicates that “free” swap is greater than “total” mem.

$ systemctl hibernate
Call to Hibernate failed: Not enough swap space for hibernation

$ free -h
               total        used        free      shared  buff/cache   available
Mem:            15Gi       6.8Gi       199Mi       2.5Gi       8.4Gi       5.8Gi
Swap:           23Gi       9.0Mi        23Gi

If it matters (which I don’t think it should), my swap partition is a btrfs subvolume on luks encrypted disk.

$ swapon
NAME           TYPE SIZE   USED PRIO
/swap/swapfile file  24G 139.2M   -2

$ mount -v | grep swap
/dev/mapper/crypted on /swap type btrfs (rw,relatime,compress=zstd:3,ssd,noacl,space_cache=v2,subvolid=260,subvol=/swap)

$ cat /etc/fstab | grep -i swap
# To make changes, edit the fileSystems and swapDevices NixOS options
/dev/mapper/crypted /swap btrfs subvol=swap 0 0
# Swap devices.
/swap/swapfile none swap defaults

$ sudo btrfs sub list / | grep swap
ID 260 gen 6590 top level 5 path swap

My disk configuration here. It uses disko, so I found it easier to just nix repl and evaluate whatever attributes you need to answer the question.

$ nix repl '.#nixosConfigurations.laptop'
Welcome to Nix 2.19.2. Type :? for help.

Loading installable 'git+file:///home/sam/box/homelab#nixosConfigurations.laptop'...
Added 9 variables.
nix-repl> config.boot.kernelParams
[ "acpi_osi=\"!Windows 2020\"" "nvme.noacpi=1" "loglevel=4" ]
(some NixOS systems would have "nohibernate" in here; not me.)

nix-repl> config.fileSystems
{ "/" = { ... }; "/boot" = { ... }; "/home" = { ... }; "/nix" = { ... }; "/persist" = { ... }; "/swap" = { ... }; "/var/log" = { ... }; }

nix-repl> config.fileSystems."/swap"
{ autoFormat = false; autoResize = false; depends = [ ... ]; device = "/dev/mapper/crypted"; encrypted = { ... }; formatOptions = null; fsType = "btrfs"; label = null; mountPoint = "/swap"; neededForBoot = false; noCheck = false; options = [ ... ]; stratis = { ... }; }

nix-repl> config.swapDevices               
[ { ... } ]

nix-repl> (builtins.head config.swapDevices).device
"/swap/swapfile"
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2

In journalctl or dmesg you may have the reason why it doesn’t want to hibernate.

For instance, if the swap file is on a BTRFS volume spread across more than 1 disk, it will refuse.

3

Neither journalctl nor dmesg contain the word “swap” or “hibernate” case insensitive. Not sure what’s going on here.

4

same configuration here and same problem
also nothing shows in my journalctl or dmesg

5

I had this error myself (couple releases ago). In my particular issue it was a systemd bug (not sure if its still a bug or the same issue your hitting). In my particular case the workaround (knowing that the swap size is of sufficient size):

# In your NixOS configuration
systemd.services.systemd-logind.environment = {
   SYSTEMD_BYPASS_HIBERNATION_MEMORY_CHECK = "1";
};
6

@Solene
good news I found some new context using @simplejack-src hacks
so at least we know where is the problem
and make this bug report
https://github.com/NixOS/nix/issues/9660

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