BUG #2691: Server did not start. Error: Could not create log file.

The following bug has been logged online:

Bug reference:      2691
Logged by:          Ille vieljans
Email address:      vieljans@augea.de
PostgreSQL version: 8.1
Operating system:   debian
Description:        Server did not start. Error: Could not create log file.
Details:

Stopping PostgreSQL 8.1 database server: main.

hostname:/etc/init.d# ./postgresql-8.1 start

Starting PostgreSQL 8.1 database server: main* Use of uninitialized value in
pattern match (m//) at /usr/share/postgresql-common/PgCommon.pm line 433.
Error: Could not create log file
 failed!
---------------
Remark:
I did not change anything at postgres.
I configured postfix, shutdown server.
On restart postgres did not start, error message above.
I repeated, the same error.