Lost oratab file ? OR Started the db with wrong ORACLE_HOME ? how to find the right ORACLE_HOME which was used to start up the oracle DB

1. A DB was started by mistake with setting different oracle home their was mutiple homes installed in test environment with 30 database running
2. Used below method
3. find the pmon process id  with ps -ef|grep pmon
4. Navigate to cd /proc folder
5. find a folder under /proc with process id  ls -lrt |grep <pmon_processid>
6. Navigate to process id folder and do ls -lrt you will find the path which was set for that process to spawn.



Example - 1
======
testhost1:orcl1:/opt/app>ps -ef|grep pmon
oracle    6237  6222  0 21:30 pts/1    00:00:00 grep pmon
oracle   28245     1  0 Feb16 ?        00:02:48 ora_pmon_orcl1

testhost1:orcl1:/opt/app>cd /proc


testhost1:orcl1:/proc>ls -lrt |grep 28245
dr-xr-xr-x  5 oracle     oinstall              0 2014-02-16 23:11 28245


testhost1:orcl1:/proc>cd 28245
testhost1:orcl1:/proc/28245>ls -lrt
total 0
-r--r--r-- 1 oracle oinstall 0 2014-02-16 23:11 stat
-r--r--r-- 1 oracle oinstall 0 2014-02-16 23:11 status
-r--r--r-- 1 oracle oinstall 0 2014-02-16 23:11 maps
dr-x------ 2 oracle oinstall 0 2014-02-16 23:11 fd
-r--r--r-- 1 oracle oinstall 0 2014-02-16 23:11 statm
-r-------- 1 oracle oinstall 0 2014-02-16 23:11 limits
-r--r--r-- 1 oracle oinstall 0 2014-02-16 23:11 cmdline
lrwxrwxrwx 1 oracle oinstall 0 2014-02-16 23:30 exe -> /opt/app/oracle/product/11.2.0.4/db_4/bin/oracle
dr-xr-xr-x 3 oracle oinstall 0 2014-02-17 22:11 task
dr-xr-xr-x 2 oracle oinstall 0 2014-02-17 22:11 attr
-rw------- 1 oracle oinstall 0 2014-02-22 01:25 seccomp
-r--r--r-- 1 oracle oinstall 0 2014-02-22 01:25 numa_maps
-rw------- 1 oracle oinstall 0 2014-02-22 01:25 mem
-r-------- 1 oracle oinstall 0 2014-02-22 01:25 environ
lrwxrwxrwx 1 oracle oinstall 0 2014-02-22 01:25 cwd -> /opt/app/oracle/product/11.2.0.4/db_4/dbs
-r-------- 1 oracle oinstall 0 2014-02-22 01:25 auxv
-r--r--r-- 1 oracle oinstall 0 2014-02-22 01:25 wchan
-r--r--r-- 1 oracle oinstall 0 2014-02-22 01:25 smaps
lrwxrwxrwx 1 oracle oinstall 0 2014-02-22 01:25 root -> /
-r--r--r-- 1 oracle oinstall 0 2014-02-22 01:25 oom_score
-rw-r--r-- 1 oracle oinstall 0 2014-02-22 01:25 oom_adj
-r--r--r-- 1 oracle oinstall 0 2014-02-22 01:25 mounts
-rw------- 1 oracle oinstall 0 2014-02-22 01:25 mapped_base
-rw-r--r-- 1 oracle oinstall 0 2014-02-22 01:25 loginuid
-r--r--r-- 1 oracle oinstall 0 2014-02-22 01:25 cpuset
testhost1:orcl1:/proc/28245>

Here the ORACLE HOME is /opt/app/oracle/product/11.2.0.4/db_4

Remember process id folder will exist for current running process.