Xen console grabbded /dev/ttyS0 : phaq : http://phaq.phunsites.net

This page was exported from phaq [ http://phaq.phunsites.net ]
Export date: Thu Apr 25 8:06:19 2024 / +0000 GMT

This week I started on evaluating an iSCSI storage system which should get connected to a Xen-enabled host. An article covering this particular topic is in preparation.

Since the iSCSI device offered management capabilities over serial console I though to attach it to COM1 (/dev/ttyS0) of my host system.
This is well the point when I noticed that Xen had already grabbed /dev/ttyS0. Since my host system offered only one serial port and I didn't have a spare serial server at hands I needed to change this behaviour to get it working.

By means of 'dmesg' it can be easily verified if Xen grabbed the serial port:



# dmesg|grep ttyS0

Xen virtual console successfully installed as ttyS0

Then make sure you know which kernel version you're running:



# uname -r

Linux gic-ftp-lin-001.genotec.ch 2.6.18-8.el5xen #1 SMP Fri Jan 26 14:29:35 EST 2007 x86_64 x86_64 x86_64 GNU/Linux

Look for the corresponding kernel section in your grub.conf (or whatever boot loader you use).



title Red Hat Enterprise Linux Server (2.6.18-8.el5xen)

        root (hd0,0)

        kernel /boot/xen.gz-2.6.18-8.el5

        module /boot/vmlinuz-2.6.18-8.el5xen ro root=LABEL=/

        module /boot/initrd-2.6.18-8.el5xen.img

Then add the 'xencons' option to the module line stating the kernel arguments.



title Red Hat Enterprise Linux Server (2.6.18-8.el5xen)

        root (hd0,0)

        kernel /boot/xen.gz-2.6.18-8.el5

        module /boot/vmlinuz-2.6.18-8.el5xen ro root=LABEL=/ xencons=tty6

        module /boot/initrd-2.6.18-8.el5xen.img

In this case I added 'xencons=tty6' to have Xen grab /dev/tty6 for it's console.

Other possibilities are:

xencons=off		disable console at all
xencons=ttyX		attach console to /dev/ttyX
xencons=ttySX		attach console to /dev/ttySX
xencons=xvcX		attach console to /dev/xvcX

After changing this line and rebooting the system I could finally connect my iSCSI's serial terminal.