I/O errors when running "head", UNLESS CD is already spinning - how to unload cache?

[FlameWeasel]

Ok, this is a weird one.

I've burned at least five DVDs and/or CDs with 6.0.2, and every single one of them does the same thing.

If I try to run the program "head" (as in, "head -5 stuff.txt", to display the first five lines of the file), and if the DVD or CD isn't already spinning, I get the error, "bash: /usr/bin/head: Input/output error". Moreover, the error is permanent until I reboot -- the error is somehow cached, so that the system *knows* that the optical disk must be hosed, and doesn't bother to retry.

If, on the other hand, I type in a few other commands, doesn't really matter what they are as long as it gets the CD/DVD spinning, then trying to run "head" works just fine and dandy. How do I get the system to un-cache the "disk is hosed" error so that I can actually run the command without having to reboot?

Note that similar problems happen when I put the system into sleep mode and then re-wake it, but they happen on EVERY command, so finding out how to clear out this cache may help prevent more problems.

[FlameWeasel]

By the way, yes, I've searched the forum. All I've turned up are threads in which it is explained that the errors are because of a bad burn to the CD or DVD. THIS IS NOT A BAD BURN. It is replicable across multiple different machines and MANY different DVDs and CDs.

Unless I've got four defective optical drives and every computer I've used the disks in is defective, again, let me reiterate that this is NOT caused by a bad burn.

[kl522]

Unless I've got four defective optical drives and every computer I've used the disks in is defective, again, let me reiterate that this is NOT caused by a bad burn.

By keep reiterating the statement, you can't convince us that it is not a bad burn or a bad knoppix image to start with. No, you can't.

You have to convince us by telling us you have done the necessary tests - testcd and sha1sum thingie. You have to convince us by telling us you have indeed burning it at the lowest speed. But you did not mentioned any of those.

So we are not convinced.