I have a user that I log in with over SFTP to my Ubuntu box. They have permission to write to the home directory of course. The external hard drive gets mounted to /media folder but I can't write to it over SFTP while logged in with that user. How would I set the permissions to allow me to write to the drive?
Unmount the drive from it's default mount point in /media.
Manually create a folder and give it suitable permissions (let's say 700).
Manually mount the drive to that folder.
Example, if the drive is formated ext4 and is installed on your system as /dev/sdb1:
Obviously you would specify the actual file system type by substituting it with ext4, and the actual device by substituting it with /dev/sdb1
You should now be able to write to the drive.
If you always have the drive plugged in, you might like to add the mount to /etc/fstab.