How to check if Oracle Database instance is up and running?

I. Log into infrastructure instance  & login as sysdba;

\$ sqlplus /nolog

SQL> conn / as sysdba;

SQL> select status from v$instance;

STATUS

------------------------------------

OPEN

II. Log into database server & issue the following command

\$ ps -ef | grep pmon

ocsinfra 11021     1   0 09:15:15 ?           0:09 ora_pmon_orcl

ocsinfra 17960 17592   0 10:47:15 pts/2       0:00 grep pmon

If DB instance is running, then the above command returns the pmon process running as above.