Slow booting and error 'Started Trigger flushing.."

"Started Trigger flushing of journal to persistent storage"    is the error message.
The cause mysterious tll I found this suggestion
I checked my swap UUID in fstab with #blkid and indeed it was wrong.
So solution:
Find out what partition your swap is

$ blkid

And alter the uuid to for instance:

/dev/sda7