[Bug 37589] Re: at boot usb hard drive is not always mount

[Martin Pitt]

It should work with your udev and fstab configuration, too; I just wanted to get the debug information under Ubuntu's default configuration.

So, if the device is not automatically mounted, and even 'mount' fails to do it, then the cause is really the sleeping, which would again make it a kernel bug.
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cannot mount usb hard drive when it's in sleep mode
https://launchpad.net/malone/bugs/37589