from the man page of fstab
auto - file system will mount automatically at boot, or when the command 'mount -a' is issued.
noauto - the filesystem is mounted only when you tell it to.
However, what I want is that usb storage device is not mounted on boot but auto mount once plugged in. Apparently make auto enabled will not automount if usb device is plugged after the system boot. Instead, one has to use #mount -a as root or $ mount blah blah as normal user to make it mounted, with the condiction that auto,nofail,user is enabled.
currently the fstab is like this:
# two entries for 340 G mobile hard disk
UUID="333c9d2f-1c2a-482e-83f7-616fa45a478a" /mnt/MobiC ext4 noauto,rw,users,exec,nofail 0 0
UUID="D0CC0864CC0846E6" /mnt/MobiD ntfs-3g defaults,noauto,users,nofail 0 0
and my system
uname -a
Linux debian 3.2.0-4-amd64 #1 SMP Debian 3.2.46-1+deb7u1 x86_64 GNU/Linux
with I3wm. I normally browse files based on command line.
more comments: I have tried fstab on boot: mount when device is plugged in and it does not work out for me.