Having spent a good amount of time working with the Xen platform, I’ve come across numerous occasions where the guest operating system would sometimes not detect disks and/or networking would not function. If you are having problems with a Linux based Xen guest, try this as a kernel argument at boot time:

xen_emul_unplug=never

I’ve used it with success on Fedora, Ubuntu, and Debian personally.

If for some reason or another you end up with a ton of e-mails in the queue and need them gone quickly, the command below will do the trick:

find /var/spool/exim/input -name '*.*' -exec rm {} \;

Most distros are now using ext4, which is great. We know that ext4 performs better than ext3. Did you know that you can make your system perform even better with a thirty second file modification?

The “relatime” option controls how ext4 records last access time information for files. By default, ext4 will modify a timestamp on a file everytime it is accessed. This may not seem like a significant performance killer, but trust me, it is. Adding relatime stops this from occurring, boosting your performance.

Your /etc/fstab file will looking something like this:

# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
#
proc /proc proc nodev,noexec,nosuid 0 0
/dev/sda3 / ext4 errors=remount-ro 0 1
# /boot was on /dev/sda1 during installation
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /boot ext3 defaults 0 2
# /home was on /dev/sda4 during installation
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /home ext4 defaults 0 2
# swap was on /dev/sda2 during installation
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx none swap sw 0 0
# ramdisk
tmpfs /tmp/ramdisk tmpfs rw,size=2G 0 0

We want to add the “relatime” option to your “/” partition. Also, your “/home” partition, if you have a separate “/home”. When done, your /etc/fstab will look more like this:

# /etc/fstab: static file system information.
#
# Use 'blkid -o value -s UUID' to print the universally unique identifier
# for a device; this may be used with UUID= as a more robust way to name
# devices that works even if disks are added and removed. See fstab(5).
#
#
proc /proc proc nodev,noexec,nosuid 0 0
/dev/sda3 / ext4 relatime,errors=remount-ro 0 1
# /boot was on /dev/sda1 during installation
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /boot ext3 defaults 0 2
# /home was on /dev/sda4 during installation
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx /home ext4 relatime,defaults 0 2
# swap was on /dev/sda2 during installation
UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx none swap sw 0 0
# ramdisk
tmpfs /tmp/ramdisk tmpfs rw,size=2G 0 0

Now, most would say to reboot your computer to have the change take effect. Not necessary. Simply run:

sudo mount -o remount /
sudo mount -o remount /home (if you have a separate /home)

Enjoy your speedier installation.

If you find that incoming mail is rejected by Exim, and you see the following in your logfile, move /var/spool/exim/db/ratelimit out of the way, and then restart Exim. Problem solved.

failed to open DB file /var/spool/exim/db/ratelimit: Bad file descriptor
Berkeley DB error: memp_fopen: page sizes must be a power-of-2