I keep on getting the above error whenever I run the following command via a postgres user.
$ /usr/lib/postgresql/9.3/bin/pg_upgrade -b /usr/lib/postgresql/9.1/bin/ -B /usr/lib/postgresql/9.3/bin/ -d /var/lib/postgresql/9.1/main -D /var/lib/postgresql/9.3/main
cannot write to log file pg_upgrade_internal.log
Failure, exiting
I'm using Ubuntu 13.10. Both Postgresql 9.1 and 9.3 are running properly.