Explicit warning when root is needed to upgrade DB

[tigergao99]

Prints an explicit warning when errmsg has the substring "readonly".
Fixes #1771

[ceri]

Could this also check that pkg isn't running as root, otherwise it's possible that this may give a misleading error explanation (if the filesystem is read-only, for example).

[tigergao99]

Thanks for the catch. Now using geteuid() to check if user is root.

[bapt]

You should also check for "install as user" concept

[grahamperrin]

Context:

% pkg update -f
pkg: Insufficient privileges to update the repository catalogue.
% pkg query %v pkg
1.18.4
% 

[kevemueller]

This looks misplaced. The SQL can err for a thousand reasons, not being able to write to the database is just one. Also the repetition does not look nice.

I believe the intention is to catch having a read-only database, which is a possible niche scenario, so not invalid per-se.

IMO the best place for this code fragment is in the error-handler that is invoked by many of the SQLite function call sites. It is located in libpkg/private/utils.h and called ERROR_SQLITE and ERROR_STMT_SQLITE.
The error condition is available and you can give more precise error messages that are pointing in the right direction for the pkg use of SQLite.
E.g. you would switch on SQLITE_IOERR, potentionally further narrow with SQLITE_IOERR_WRITE (778), perform your geteuid test and have the proper explanation in the error message.

Would that be a possible way forward for you?