March 2014 Archives

Direct connect to HVM serial ports

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Me and Luke recently got this question:

"So with both pv and hvm domains you can pull out the virtual tty via xenstore-read /local/domain/[domain]/console/tty . However, with pv domains you can use the tty directly with something like screen /dev/tty/blah but with a hvm domain that ends up giving you a blank screen. What's even weirder is that when you look at the source of xm console it doesn't seem to differentiate between the two, and yet it works fine on both.

Any ideas?"

We are using xl on xen 4.3, not xm, on our test machine but in theory these should be doing mostly the same thing.

Using the command "strace -f xl console ubuntu-1 &> con" I found this in the output of strace:

[pid 30642] access("/dev/pts/2", R_OK|W_OK) = 0
[pid 30642] open("/dev/pts/2", O_RDWR|O_NOCTTY) = 8

Searching back for /dev/pts/2 I found the following:

[pid 30642] write(5, "/local/domain/356/serial/0/tty\0", 31) = 31

Therefore it looks like the key is


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