Backend crash

I am facing some problem while using postgres (version 7.3.1)

On trying to execute a psql command  from the postges interactive terminal
as user 'test' (which exists in the pg database), pgsql seems to be
crashing.

The postmaster log file contains the following -
--------------------------------------------------------------------------------
WARNING:  ROLLBACK: no transaction in progress
FATAL:  Password authentication failed for user "test"
LOG:  fast shutdown request
LOG:  shutting down
.......
StreamConnection: accept() failed: Connection aborted
------------------------------------------------------------------------------------


Can anyone please tell me why postmaster is shutting down ?   What all
causes the SIGINT signal to be sent to postmaster that causes rollback of
open transactions and  disconnection of open connections ?

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