Xen console grabbded /dev/ttyS0
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.
July 9th, 2007 at 5:00 pm
Thanks much. I’ve spent a week on and off looking around, looking for a good simple fix.
November 13th, 2007 at 1:11 pm
hello,
when I run command:::::::::::::::::dmesg |grep tty
Xen virtual console successfully installed as ttyS0
I am not getting whats actually going on with my serial ports…..
I am writing code which is fully dependent on setial communication….due to this I am not able to use my serial port.
1.)So any method to come out of this problem…….
2.)Moreover can you guide me in details what is this virtual console….and why it is not allowing me to use my serial port…..
3.)Steps to follow while doing serial programming.
4.) Any commands which can verify that my serial port is recieving data or sending data or any tool to do such …..
thanks & regards,
Arun
November 23rd, 2007 at 9:38 pm
@arun
1. my article says exactly how to disable the xen virtual console
2. for information about Xen virtual machine monitor please read the fine manual at http://www.cl.cam.ac.uk/research/srg/netos/xen/
You will have to figure 3. and 4. on your own, I have no experience in serial port programming at all.
Greeetings
Gianpaolo
August 14th, 2008 at 12:17 am
well after much bashing brains i figured it out to get console
working enabling bios redirect -> kernel messages -> booted login console.
disable in grub.conf or bios redirection will cause grub to hang!
Let bios do the redirection not grub!!!!
#serial –unit=0 –speed=9600
#terminal –timeout=0 serial console
set options as so for kernel
kernel /boot/xen.gz-2.6.18-92.1.6.el5 com1=9600 console=com1
module /boot/vmlinuz-2.6.18-92.1.6.el5xen ro root=LABEL=/ xencons=xvc console=xvc
module /boot/initrd-2.6.18-92.1.6.el5xen.img
then in your /etc/inittab add entry
by the runlevels:
SC:12345:respawn:/sbin/mingetty xvc0
1:2345:respawn:/sbin/mingetty tty1
…
There you go finally the xen ttys0 nuisance is consolable!
September 13th, 2010 at 3:17 pm
Thank you! Though this article has been around for awhile it took me a surprising amount of time to find it. I needed ttys0 for the new APC UPS that we installed, and couldn’t figure out how to connect it. I finally found an article from APC that with Xen installed, the APC may not work over a com port. Which eventually led me here. Thanks for documenting the fix.