I can purge a snap package with
snap remove --purge myPackage
But what if I already removed it, without the --purge flag? With apt, I can still do sudo apt purge myPackage, even after an uninstall, but not with Snap, it seems. Do I have to install it again, to remove it a second time with the purge flag, or is there another way I missed?
See what the Snap Docmentation tells us about removing snaps.
The only difference is a snapshot of user-data and configuration-data which is only taken when you don't use the --purge-option. This snapshot will be kept for 31 days.
So you don't really need to do anything, the snapshot will be removed after that period by the snapd service.
If you are somehow in a hurry or the snapshot contains sensitiv data which you want to remove as soon as possible, take a look with snap saved for existing snapshots and use snap forget to remove a snapshot. Example:
~$ snap saved
Set Snap Age Version Rev Size Notes
4 wire 14.8d 3.24.2939 237 982kB -
~$ snap forget 4
Snapshot #4 forgotten.
~$ snap saved
No snapshots found.
Feel free to take a deep look into man snap.
Just for completeness: Snapshots are stored as zip-archives in /var/lib/snapd/snapshots/.
