I had a similar problem, but the cause turned out to be different for
me.
I had changed the GID of group tty from 5 to 11. I later found out that
this contravenes the Ubuntu standard GID policy.
The symptom was similar to the above
chardev: opening backend "pty" failed: Exec format error
It turns out that "Exec format error" is the string given by
errno=ENOEXEC.
After some investigation of my problem, it turns out that (in my case) the
failure was occurring at
qemu-char.c:997 if (openpty(&master_fd, &slave_fd, pty_name, NULL, NULL) <
0) {
The call to openpty was failing because the directory /dev/pts had a gid of 11
instead of a gid of 5.
The error was issued because the directory /dev/pts did not have the
appropriate exec permission to be able to create a new device file within it.
I changed around my GIDs to match the standard values, and that was
enough to fix the problem (for me).
Note that /dev/pts is a MOUNTED filesystem of type devpts. The gid of the mount
can be found by typing mount.
In my case, kvm fails when set as follows
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=11,mode=0620)
GOOD: kvm works:
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
I acknowledge that this problem is a bit different from the subject of
this bug, but this is the closest bug I found to my problem when I
initially came across it.
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https://bugs.launchpad.net/bugs/632696
Title:
libvirt won't start a VM with serial or console
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