KVM Virsh Console Access to Linux VM – CentOS 6
virsh console grub ttyS0
This document will show you how to get virsh console access to guest virtual machines.
The console command within virsh is an excellent feature to have working for your virtual environments. For example, it can be really handy to watch a machine boot without launching a GUI tool ie. virt-manager. I personally find virsh console access a quicker way to configure networking settings which may not be able to be achieved via SSH, other than using virt-manager.
Just note that this document assumes CentOS 6 for all example code and references. Syntax, file locations and codes may vary based on your distribution.
Typically out of the box, when you install a new CentOS 6 virtual machine, the “virsh console” command will not work…
Step 1: Configure Serial Terminal
On your new CentOS 6 virtual machine, you’ll need to configure ttyS0. This serial interface is how “virsh console” gains access to your virtual machine.
Log into your virtual machine…
Create new ttyS0 config file
Copy/Paste the following config
stop on runlevel[016]
start on runlevel[345]
respawn
instance /dev/ttyS0
exec /sbin/mingetty /dev/ttyS0
Step 2: Allow login into ttyS0
By default CentOS will not allow a user to login via ttyS0 unless we modify securetty.
Step 3: Start ttyS0
Make ttyS0 available, from your terminal execute the following command
Step 4: Test Virsh Console
From your KVM server, connect to the console of your virtual machine
# virsh console centos_template
Connected to domain centos_template
Escape character is ^]
CentOS release 6.3 (Final)
Kernel 2.6.32-279.14.1.el6.x86_64 on an x86_64
localhost.localdomain login:
Step 5: Configure Access to Boot Output
To watch your virtual machines boot/shutdown messages we need to make a couple of changes to your boot process.
Edit your grub config
Your kernel entry may look something like this
kernel /vmlinuz-2.6.32-279.14.1.el6.x86_64 ro root=/dev/mapper/VolGroup-lv_root
rd_NO_LUKS LANG=en_US.UTF-8 rd_NO_MD rd_LVM_LV=VolGroup/lv_swap
SYSFONT=latarcyrheb-sun16 crashkernel=auto
rd_LVM_LV=VolGroup/lv_root KEYBOARDTYPE=pc KEYTABLE=us
rd_NO_DM rhgb quiet
You’ll want to remove the “rhgb” option, this is the boot splash screen. The “quiet” entry hides a lot of boot messages, I remove so more detail is outputted.
Finally you’ll want to add “console=ttyS0” to send the boot messages to your virsh console. Your kernel line may now look like this