Re: QEMU hangs, apparently while polling dbus

[Steve Litt]

This is a piece of information that may or may not relate to what
you're seeing. Over 10 years ago, with Kmail running, one of the
dbus-daemon processes would start consuming 95+% of CPU. This happened
several times a day. I finally fixed it by creating my own daemon,
which would use ps to find any dbus-daemon instances over 90%, and if
it was still over 90% five seconds later, my daemon would kill it.

So, I recommend when this hangs, you take a look at the ps command.

By the way, I gave up Kmail in 2012 and never had this problem again.

SteveT

Steve Litt 
March 2022 featured book: Making Mental Models: Advanced Edition
http://www.troubleshooters.com/mmm


Parke said on Wed, 9 Feb 2022 22:42:32 -0800

>On my system, the command `qemu-system-x86_64` prints no output and
>simply hangs.  No display window appears.  Apparently QEMU hangs while
>polling dbus.
>
>If I run `strace qemu-system-x86_64`, the end of the output is:
>
>socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0) = 8
>connect(8, {sa_family=AF_UNIX, sun_path="/tmp/dbus-4fpXSf1PZL"}, 22) =
>0 fcntl(8, F_GETFL)                       = 0x2 (flags O_RDWR)
>fcntl(8, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
>geteuid()                               = 1000
>getsockname(8, {sa_family=AF_UNIX}, [128 => 2]) = 0
>poll([{fd=8, events=POLLOUT}], 1, 0)    = 1 ([{fd=8, revents=POLLOUT}])
>sendto(8, "\0", 1, MSG_NOSIGNAL, NULL, 0) = 1
>sendto(8, "AUTH EXTERNAL 31303030\r\n", 24, MSG_NOSIGNAL, NULL, 0) = 24
>poll([{fd=8, events=POLLIN}], 1, -1
>
>My system is running Ubuntu, but I installed Ubuntu manually (using
>custom scripts I wrote), so it is entirely possible that dbus is not
>behaving as expected.  (I have deliberately disabled or removed many
>Ubuntu components that are present on a "standard" installation of
>Ubuntu.)
>
>Is it possible to prevent QEMU from attempting to use dbus?
>
>Does anyone have any suggestions for diagnosing the problem?  QEMU is
>not printing any error or diagnostic messages.  If dbus writes any
>error or log messages, I don't know where they would be.
>
>If I move the socket /tmp/dbus-4fpXSf1PZL to some other path, then it
>appears that QEMU runs successfully.  (Presumably, in this case QEMU
>skips trying to connect to dbus.)
>
>Thank you,
>
>Parke
>