[plug] Statically Mounting USB Drives

[Daniel Pittman]

Jason Posavec <jasonposavec at iinet.net.au> writes:

> I can't seem to solve this problem, so I'm trying to find out if it
> *can* actually be solved. 

Yes.

> I want to have USB drives as a permanent part of fstab. More
> specifically, a USB thumb drive connected on one of the internal
> motherboard connecters to run as my swap drive. Problem seems to be
> that depending on what external USB drives may or may not be switched
> on at boot time, Linux (and presumably any OS) seems to be a bit
> random in the order it mounts USB drives.

It is, in large part because scanning the USB bus is an asynchronous
process and, so, multiple devices will report differently on alternate
boots.

> Anyone know of a way it can be done statically?

Yes.  Assuming you are running a relatively recent distribution you
should have a number of persistent names for your device created by the
udev process.

That creates symbolic links from /dev/disk/by-{id,label,path,uuid} to
the device node assigned.  So, it doesn't matter if your USB disk is
/dev/sda, /dev/sdz, or /dev/magic-unicorn, you can refer to one of those
persistent names.


Better still, your mount command almost certainly supports the same sort
of persistence.  You should be able to specify, in fstab, a device of:

    UUID=aoeui....
    LABEL=hello

That will (depending on the version of mount) either scan available
devices to find the matching hardware, or simply use those udev created
aliases.


As an aside, this is a good policy for *all* your drives, not just the
USB or other "dynamic" disks.  Your SATA and PATA disks can renumber if,
say, you connect a USB disk at boot, or plug in an additional controller
card, or even frob random BIOS options in many cases.

Using a persistent name rather than a hardware name makes your system
independent of that renumbering, and makes you happier in the long run.


Most distributions, these days, actually use this sort of persistent
name mounting when you install, also.

Regards,
        Daniel