Oracle did not start listener when use "dbstart"

when I try to use dbstart in solaris, I found this error.

oracle# dbstart
ORACLE_HOME_LISTNER is not SET, unable to auto-start Oracle Net Listener
Usage: /oracle/product/10.2.0/db/bin/dbstart ORACLE_HOME
Processing Database instance "wp0": log file /oracle/product/10.2.0/db/startup.log

*** Oracle start the process but did not start listener ***
oracle# ps -ef |grep ora
oracle 8207 1 0 18:48:53 ? 0:00 ora_lgwr_wp0
oracle 8211 1 0 18:48:53 ? 0:00 ora_smon_wp0
oracle 8225 1 0 18:49:01 ? 0:00 ora_qmnc_wp0

oracle# telnet 10.1.40.12 1521
telnet: Unable to connect to remote host: Connection refused

I solved this problem by use dbstart and following parameter $ORACLE_HOME

*** Try again with parameter ***
oracle# dbstart $ORACLE_HOME
Processing Database instance "wp0": log file /oracle/product/10.2.0/db/startup.log

telnet 10.1.40.12 1521
Trying 10.1.40.12...
Connected to 10.1.40.12.
Escape character is '^]'.

It's work!!!!!

== TaTsHuYa ==