35.6. Troubleshooting with the serial console

The serial console is helpful in troubleshooting difficult problems. If the Virtualization kernel crashes and the hypervisor generates an error, there is no way to track the error on a local host. However, the serial console allows you to capture it on a remote host. You must configure the host to output data to the serial console. Then you must configure the remote host to capture the data. To do this, you must modify these options in the grub.conf file to enable a 38400-bps serial console on com1 /dev/ttyS0:
title Red Hat Enterprise Linux (2.6.18-8.2080_xen0)
	root (hd0,2)
	kernel /xen.gz-2.6.18-8.el5 com1=38400,8n1 
	module /vmlinuz-2.618-8.el5xen ro root=LABEL=/rhgb quiet console=xvc console=tty xencons=xvc 	
	module /initrd-2.6.18-8.el5xen.img
The sync_console can help determine a problem that causes hangs with asynchronous hypervisor console output, and the "pnpacpi=off" works around a problem that breaks input on the serial console. The parameters "console=ttyS0" and "console=tty" means that kernel errors get logged with on both the normal VGA console and on the serial console. Then you can install and set up ttywatch to capture the data on a remote host connected by a standard null-modem cable. For example, on the remote host you could type:

Note

To access the hypervisor via a serial console on the Itanium® architecture you must enable the console in ELILO. For more information on configuring ELILO, see Chapter 30, Configuring ELILO.
ttywatch --name myhost --port /dev/ttyS0
This pipes the output from /dev/ttyS0 into the file /var/log/ttywatch/myhost.log .