19.6. 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 Xen host to
output data to the serial console. Then you must configure the
remote host to capture the data. To 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 Linix (2.6.18-8.2080_RHEL5xen0)
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:
ttywatch --name myhost --port /dev/ttyS0
This pipes the output from /dev/ttyS0 into the file
/var/log/ttywatch/myhost.log .