USB device activity when not mounted

Daniel Feenberg feenberg at
Thu Jun 14 13:55:51 UTC 2012

On Thu, 14 Jun 2012, Mike Clarke wrote:

> On Thursday 14 June 2012 07:05:11 Polytropon wrote:
>> I don't think that's a problem. I've got a USB stick here
>> that has a blinkenlight as soon as it's powered on (plugged
>> in), even if there is no reading / writing / mounting activity.
>> After you've successfully performed umount, the USB stick _is_
>> synced and can safely be removed, no matter what you assume
>> the funny lights want to tell you.

Is it possible that there is volitile memory buffering in the stick that 
may not have been written to flash when umount thinks it is complete, and 
the flashing light is an indication that power is still required to 
complete the write to non-volitile memory?

Futhermore, are we sure that umount even waits for a sync? There is no 
mention of that in the man page and I don't recall any long waits for 
umount to return.

daniel feenberg

More information about the freebsd-questions mailing list