how to mount / partition as read only

[umer]

Dear All,

I Want to mount / partition is read only.when i use the following command its prompt me that / is busy

mount -o remount,ro /

I am New to Linux please to mount / partition is read only

Thanks

[protocentux]

You can use the lsof command to check which processes are using that filesystem.
i.e.
bash# lsof /

Make sure you are not in a folder that belongs to that filesystem.
Regards,
Protocentux.