Thanks a lot for your advise.
I tried to do
$psql -h localhost -p 5432 -U seruser -W ser
Connecting database ser is success.
But in the log file, these following lines appeared
after SER started using /usr/sbin/ser command.
FATAL: Non_superuser connection limit exceeded
LOG: pq_recvbuf:unexpected EOF on client connection
Maybe this is the reason database doesn't work, I think.
It seems SER can't connect to postgres.
What should I do?
Another problem: SER processes don't stop using /usr/sbin/ser stop.
Many SER processes are surviving.
Is it strange?
Most sincerely
Takefumi