Is it possible to truncate the pg_largeobject table in postgres?

Question

I would like to discard the contents of the pg_largeobject table and reclaim its disk space. When I try issuing this command:

truncate pg_largeobject

I get this response:

ERROR:  permission denied: "pg_largeobject" is a system catalog

This is even though I am issuing the command as user postgres (a superuser). There is insufficient disk space to do a VACUUM FULL while the table contains a lot of rows. I've also tried just deleting all the rows in preparation for a VACUUM FULL, but this was still going after a whole day, and ended up being interrupted. I'd prefer to truncate if at all possible.

Is truncation of this table possible? It currently contains around 1 TB of images I no longer want. I've removed references to the table from all my other tables (and deleted all rows from pg_largeobject_metadata).

Answer 1

Turning on allow_system_table_mods was the answer. The truncate then took only a few minutes. Thanks to Nick Barnes for this suggestion and to an old article that confirmed this approach.