SQLite Forum

unable to open a database file in a btrfs readonly snapshot filesystem
Is your DB in *WAL* mode?  
I assume it is, otherwise read-only would have worked.

If so, does it use the *Persistent WAL* option?  
By preventing the -SHM file to be deleted on checkpoints,  
I think you can open still open that DB in readonly mode then.

Although WAL is part of the DB file itself (i.e. persistent),  
keeping the -SHM around is not, all your connections need to set it. (I believe).