Steve Glendinning » Lenny

Found a new toy: sshfs

Steve — Fri, 06 Nov 2009 10:26:29 +0000

I just discovered sshfs. This allows you to mount a remote filesystem using nothing at the server end other than a standard ssh server.

Once installer, as a non-root user you can just:

mkdir mnt sshfs username@server.domain.com:/path mnt

Then you can access it, copy files etc (both directions) as if it were a local directory

ls mnt

When finished this disconnects it:

fusermount -u mnt

Found at http://home.prea.net/hacking/X2200/NFS

Time went backwards

Steve — Mon, 23 Mar 2009 10:06:42 +0000

I just applied a hotfix to my XenSource virtual servers, which caused all the virtual machines to be suspended & resumed (while the xen host rebooted). This caused a problem on the VMs I’ve upgraded to Debian Lenny: These messages were repeatedly logged:

clocksource/0: Time went backwards: ret=18f26176a5 delta=-8292949932632971 shadow=18e9e0b4b9 offset=880c4ce

This message wasn’t “harmless” – it caused TCP connections to break, so ssh was practically unusable.

The immediate solution: using the XenCenter console, forcefully reboot the affected VM. That’s “force shutdown”, followed by “start”. I tried the simple “reboot” option, but it wouldn’t shut down (probably because it was confused over the time). VMs are now back up and there’s no sign of time going backwards.

It seems this was triggered by suspending & resuming machines running the Debian Lenny kernel. Other VMs which are still running the 2.6.18 based XenSource kernels survived suspend/resume ok.

The actual cause is documented here, here, here & here. I think I’ll be following that advice and decoupling my VM clocks from the host (using NTP to keep them all in sync the old-fashioned way).

Upgrading Xensource Debian Etch guests to Lenny

Steve — Sun, 15 Feb 2009 16:44:21 +0000

Debian Lenny has been released, so I’ve started upgrading some of my Xen virtual servers. For Etch, Xensource shipped their own modified PV kernel package (2.6.18 based). With Lenny the same kernel can be used, or the standard Debian xen kernel (2.6.26 based) can be used instead.

Upgrading the userland is identical to a physical server – instructions are contained within the Debian Lenny release notes.

To use the Debian packaged 2.6.26 kernel, several minor changes have to be made as per this form post:

Install the linux-image-2.6-xen-686 package (which depends on the latest xen kernel)
Re-order the kernels in /boot/grub/menu.lst so the Debian 2.6.26 kernel is the first (and therefore the default)
Add “console=hvc0″ to the end of the 2.6.26 kernel line in /boot/grub/menu.lst, so it reads “kernel /boot/vmlinuz-2.6.26-1-xen-686 root=/dev/xvda1 ro console=hvc0“
edit /etc/inittab, find the line that looks like “1:2345:respawn:/sbin/getty 38400 tty1″ and add another line: “0:2345:respawn:/sbin/getty 38400 hvc0″

Then reboot the system, it should boot the new kernel.

Xensource doesn’t display the grub menu, it just seems to boot straight into the default option (even though I have “timeout 10″ specified in the config). There must be a secret keypress or something to make it show the menu, but I don’t know what it is because the last step just worked for me!

Edit: Theoretically you shouldn’t need to use the -xen kernel variant, as the -686-bigmem kernel also supports running paravirtualised in domU. With Xensource 5.0 this boots fine, but Xensource’s xen-tools refuse to start so XenCenter reports the status as “unknown”. With the -xen kernel xen-tools start fine.