On this host /mnt has 755 perms while /mnt/backup and /mnt/hd both have 777 perms. I and root can write to /mnt/backup but neither of us can write to /mnt/hd. Both file systems have default options in /etc/fstab.
My web searches haven't found a reason why the one is writable by all and the other is read-only to all. Any ideas why? Rich