What is the best way to leave a file/directory behind (not delete) after removing a snap application?
Use case: cryptocurrency wallet where a user could accidentally remove the application and now the wallet file is gone forever. The user would be upset and out of money if he/she doesn’t backup the file.
Currently there is no way to do this. Speaking in general it would be awesome if snapd could generate and restore backups. Since we know where the data is already this should not be difficult.
As for your specific question I think it is interesting, it is not (perhaps) immediately clear that removing a snap will remove its data. CC @chipaca
snappy (in 15.04) had separate remove and purge steps for this, but we abandoned that in favour of the current simpler model as it wasn’t well received nor understood.
I agree separate purge is confusing but I’d say that as a user I’d like to be able to remove a snap and keep my data easily, without being a developer. We should explore a story for this.
perhaps adding a --keep-user-data switch to “remove” might make sense (so it is an explicit thing)
We can make many small steps but I think what is needed is good overall experience. The person who lost their wallet would not have used --keep-data without knowing about it.
for that case it might perhaps make more sense to allow snaps to add a Y/N question to the removal process via a snapcraft.yaml option … (seems like we have two bugs here … one to keep data on demand, one to make sure a user doesnt accidentially remove an important snap)
Yes, I was thinking about very-precious-data: bool key imagining snap remove home-family-photo-collection but then again, is there any snap that actually keeps data that is not valuable. Will this option degrade to just true.
Maybe we want $SNAP_PRECIOUS_USER_DATA which is like $SNAP_USER_DATA but is automatically backed up and kept until removed explicitly.
Note this is a very old request with specific direction from snappy architects. While I happen personally to agree with the sentiment of the request, if this is going to be revisited, we need an architect to comment and participate in the new direction (cc @niemeyer).
My 2 cents which I guess is similar to zyga
$SNAP_USER_PERMANENT_DATA will store non versioned user data that will persist after removal of the application unless specifically requested to delete via yes/no question, dialog box or command line flag.
snap remove myapp will produce a yes/no question.
snap remove myapp --delete-permanent
I’m hoping we can solve this problem by introducing snapshots, which is a first class representation of the storage and data associated with a snap in the system (not just the data). Such snapshots would not include the snap file itself. Only the data in use at a time and metadata for the snap, including the snap configuration, etc.
This is certainly an important stepping stone towards introducing backups, and perhaps most of the functionality as far as snapd is concerned, but I would reserve the term “backup” for something that actually takes the data offsite.
Quick strawman as a hint of what snapshots would be:
| Command | Summary |
|---|---|
snap saved |
Lists currently stored snapshots |
snap save bitcoin |
Take a snapshot of the bitcoin snap |
snap lose bitcoin |
Delete all snapshots of the bitcoin snap |
snap lose bitcoin 32 |
Delete the specific snapshot of bitcoin |
snap squash bitcoin 32 |
Replace data currently in use by bitcoin with snapshot 32 |
snap remove bitcoin |
Remove bitcoin and save current data in a temporary snapshot |
snap purge bitcoin |
Remove bitcoin snap and immediately drop current data |
The temporary snapshot created on remove is maintained for N weeks, and we can allow the snap to define the amount of time to keep that snapshot (edit: spelled as short/medium/long term, see below). The user should be able to turn that snapshot into a persistent one if desired.
How does that sound?
#1 This type of functionality sounds great! Whether it solves this specific problem or not, it should be added.
#2 Will this user even know this functionality is there? What’s the chance a user removes the app and remembers months later (will the backup snapshot be rotated out by then)? What happens a user runs out of space and starts clearing up things like the app and snapshots (as weird as it sounds, so many users clear backups first)?
The functionality is great. I feel giving developers options to create persistent data directories that would be snapshot’d is the best combination/solution.
There’s indeed some tension between never losing important data and never recovering wasted space. For example, it’s easy to argue that if one removes a snap without saving its data, and doesn’t even go after the data at all for a long time, the data was indeed not very relevant and should have been removed in the first place.
So the intent of the proposal is recognizing that and giving a chance for recovery of important data, while at the same time not wasting space forever on unimportant data.
Instead of defining the number of weeks, we should probably support three levels instead: short term, medium term, and long term, and we can then define and polish over time how each of these behaves. We might end up warning people about the long term ones instead of removing straight out, for example.
Has this issue been solved? I am having the same issue. Someone suggested I use ~/snap/app/common to store app data but on snap remove even that dir is being deleted…
$SNAP_USER_COMMON should be kept around when you remove a snap with snap remove <some-snap>. If it’s not, please start a new forum topic or LP bug to discuss this, as that sounds like a bug if you are seeing it get removed.
I thought they did get removed (I actually experience that myself). A backup is made on snap remove though, which I think can be listed with “snap saved”, but I don’t know if there is a way to export that.
Sorry I guess I am mistaken we do remove all the data, I confirmed this looking at the code. I really thought we changed that but apparently we have not. Indeed if you have not disabled snapshots however when you remove a snap you can restore the data that was removed with snap restore. If you disabled snapshots by setting snapshots.automatic.retention then you will not have these snapshots, but by default the snapshots are enabled.
So, then what is the best way to store the data of a snap so that it is not removed on snap remove? I don’t know if the users of my app will know how to retain their data through snap commands… Is there a place where I can store permanently the data of my app? Is the real home directory the only way? I would prefer avoiding special permissions for my app tho
It is for me completely unexpected that removing the Snap application also removes the user data from the home directory, without warning. This is contrary to how all other GNU/Linux applications / package managers do their file housekeeping, the system wide and home directory specific files management used to be strictly separated, and package managers were never responsible for the contents of the home directories.