initdb using option "username" startup log

I initdb like below
"initdb --pgdata=/pg_data --encoding='utf8' --locale='C' --lc-collate='C'
--lc-ctype='C' --username=sys --pwprompt"

When startup database server.
Server wirte log like this
-----------------------------
LOG: database system was shut down at 2012-10-31 12:00:14 KST
LOG: database system is ready to accept connections
LOG: autovacuum launcher started
FATAL: role "postgres" does not exist
-----------------------------

*What is it ? : FATAL: role "postgres" does not exist*

P.S process list
[postgres(at)pg111 pg_log]$ ps auxww | grep ^postgres
postgres 13920 0.0 0.0 108300 1952 pts/1 S 10:54 0:00 -bash
postgres 14588 0.0 0.1 153732 7108 ? S 12:00 0:00
/postgresql/9.2.1/bin/postgres -D /pg_data
postgres 14590 0.0 0.0 153732 940 ? Ss 12:00 0:00 postgres:
checkpointer process
postgres 14591 0.0 0.0 153732 1004 ? Ss 12:00 0:00 postgres:
writer process
postgres 14592 0.0 0.0 153732 900 ? Ss 12:00 0:00 postgres:
wal writer process
postgres 14593 0.0 0.0 154432 1908 ? Ss 12:00 0:00 postgres:
autovacuum launcher process
postgres 14594 0.0 0.0 113420 788 ? Ss 12:00 0:00 postgres:
stats collector process
postgres 14612 0.0 0.0 110224 1152 pts/1 R+ 12:01 0:00 ps auxww
postgres 14613 0.0 0.0 103236 864 pts/1 S+ 12:01 0:00 grep
^postgres

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