[CentOS-virt] How to add additional Serial Ports to a KVM guest?

James B. Byrne byrnejb at harte-lyne.ca
Thu Dec 1 12:11:56 EST 2011

The vm host shows this:

#  setserial -g /dev/ttyS*
/dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4
/dev/ttyS1, UART: 16950/954, Port: 0xd040, IRQ: 17
/dev/ttyS2, UART: 16950/954, Port: 0xd048, IRQ: 17
/dev/ttyS3, UART: 16950/954, Port: 0xd050, IRQ: 17
# ll /dev/ttyS*
crw-rw----. 1 root dialout 4, 64 Nov 10 12:18 /dev/ttyS0
crw-rw----. 1 root dialout 4, 65 Nov 10 12:18 /dev/ttyS1
crw-rw----. 1 root dialout 4, 66 Nov 10 12:18 /dev/ttyS2
crw-rw----. 1 root dialout 4, 67 Nov 10 12:18 /dev/ttyS3

By default serial 0 o guests is assigned to pty and has a
device path of '-'.  I have installed on the host a 4-port
serial card, as evidenced above.  When I add the first
additional port to the guest (serial 1) and use
'/dev/ttyS1' as the path the guest will boot.  However, if
I add a second serial port (serial 2) using path
'/dev/ttyS2' then I get this error and the guest will not

Traceback (most recent call last):
  File "/usr/share/virt-manager/virtManager/engine.py",
line 878, in run_domain
  File "/usr/share/virt-manager/virtManager/domain.py",
line 1313, in startup
  File "/usr/lib64/python2.6/site-packages/libvirt.py",
line 333, in create
    if ret == -1: raise libvirtError ('virDomainCreate()
failed', dom=self)
libvirtError: internal error Process exited while reading
console log output: char device redirected to /dev/pts/1
isa irq 4 already assigned

How does one configure additional serial ports on a kvm

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James B. Byrne                mailto:ByrneJB at Harte-Lyne.ca
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Hamilton, Ontario             fax: +1 905 561 0757
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