The following bug has been logged online:

Bug reference: 1894
Logged by: Gerhard Kirchmann
Email address: gerhard.kirchmann (AT) arcor (DOT) de
PostgreSQL version: 8.1beta2
Operating system: Linux x86
Description: postmaster does not start
Details:

After installing 8.1.beta2 (and 8.1.beta1)
and after having performed an initdb (which produced no error)
starting postmaster always ends in the following error messages within the
file serverlog:
LOG: could not bind IPv4 socket: Die Adresse wird bereits verwendet
HINT: Is another postmaster already running on port 5432? If not, wait a
few seconds and retry.
FATAL: database files are incompatible with server
DETAIL: The database cluster was initialized with PG_CONTROL_VERSION 74,
but the server was compiled with PG_CONTROL_VERSION 811.
HINT: It looks like you need to initdb.

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