While reading online, somewhere I have read that I will need to disable journaling in Mac OS partition to mount it on Ubuntu with writing permission. I wanted to do the same but I saw the Enable/Disable Journaling button is not enabled in Disk Utility. So, after searching I found a command to do that from command line. It is simple.
# diskutil disableJournal /Volumes/Macintosh HDThat’s it. It disabled journaling on that partition. Later on Ubuntu I mounted the drive and I could write on it.
Mounting the partition on Ubuntu
sudo mount -t hfsplus /dev/sda2 /media/mac