A short one. 

If you're trying to hibernate your system but it doesn't shut down, you'll probably try again. After a few attempts[^1], 
you go check `dmesg` and find this error message:

    PM: Image saving failed: -28
    
I only thought about it now, but `-28` is `ENOSPC`, no space error. This means that what you have in memory and swap 
does not fit in swap, even when it's compressed, which is how hibernate works:

    $ free -h
                total        used        free      shared  buff/cache   available
    Mem:            31Gi        14Gi        12Gi       2.7Gi       7.0Gi        16Gi
    Swap:           47Gi        40Gi       7.8Gi

Unluckily, there's nothing that bubbles up this error to the user interface; hence, the retrying.

In my case, the solution was to stop the program that was using a lot of memory, but another one would be to create a 
temporary swap file big enough.

[^1]: my logs say I tried 4 times!