Mount Options

How to mount a hard disk as read-only from the terminal
You do not mount '''/dev/sda''', that refers to the entire disk. You mount '''/dev/sda1''' or whatever partition you want. Make a mount point, call it anything you like. 
 sudo mkdir /media/2tb
 
 Mount as Read Only 
 sudo mount -o ro /dev/sda1 /media/2tb
 
 When your done, you should unmount the disk 
 sudo umount /media/2tb
 
 See man mount or https://help.ubuntu.com/community/Fstab

Mount SSH / SSHFS / SFTP
sudo sshfs -o uid=1000 -o gid=1000 -o allow_other user@remotehost:/path/to/folder/ /path/to/local/dir