Un-killable Processes : Red Hat Enterprise Linux

By Johnathan Kupferer, Red Hat Certified Engineer

Before Red Hat Enterprise Linux 4, there really wasn’t a good way to handle processes that had entered an
uninterruptible sleep waiting on an unresponsive NFS server. This was particularly frustrating because the
umount man page promises that “-f” will “Force unmount.” This allows an NFS-mounted filesystem to be
unmounted if the NFS server is “unreachable.” That was how it was supposed to work, with the caveat that
the filesystem must have originally been mounted with “soft” or “intr” options.Well, no more. Though the
man page doesn’t say so, umount -f now comes to the rescue and will unmount hard and uninterruptible
mounts.

USB when the Drivers Aren’t Available

By Dominic Duval, Red Hat Certfied Engineer

As a way to save a few valuable pennies on newer PCs, manufacturers are increasingly getting rid of the good old PS/2 keyboard and mouse interfaces. As a result, some recent systems only ship with USB ports to which we need to connect a USB keyboard and mouse.
USB is all well and good, but what if the driver for your USB controller is not loaded? In practice, this is not a problem, as Red Hat loads the ehci- hcd and uhci-hcd drivers automatically at boot time.
There are situations, namely in emergency mode, where the USB drivers won’t be available. So you won’t even be able to enter a command. This is due to the fact that in emergency mode all drivers need to be provided in the initrd file under /boot, and USB is not there by default. The trick is to add those drivers, so that they will be available earlier. The ‘mkinitrd’ command can do precisely that with the ‘–with’ argument (this only works under RHEL4):
mkinitrd –with=ehci-hcd –with=uhci-hcd /boot/newinitrd-`uname -r`.img `uname -r`

Add a new entry in your grub.conf file (always do backups!) that points to this new initrd image, and you’re done! Your USB keyboard now works in emergency mode.

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