Comment 8 for bug 1752411

I ran into this myself today after upgrading a machine to bionic..

two copies of it running at once.. both stuck on host.
If I execute a new 'host' command it works, but the existing ones are stuck.l

root 14181 0.0 0.0 4628 868 ? Ss 13:05 0:00 /bin/sh -c cat /run/systemd/resolve/stub-resolv.conf | /sbin/resolvconf -a systemd-resolved
root 14292 0.0 0.0 4520 752 ? S 13:05 0:00 run-parts --arg=-a --arg=systemd-resolved /etc/resolvconf/update.d
root 14320 0.0 0.0 4520 748 ? S 13:05 0:00 run-parts /etc/resolvconf/update-libc.d
root 14354 0.0 0.0 4628 1672 ? S 13:05 0:00 /bin/sh /usr/lib/avahi/avahi-daemon-check-dns.sh
root 14607 0.0 0.0 187532 8380 ? Sl 13:05 0:00 host -t soa local.

root 13775 0.0 0.0 4628 868 ? Ss 13:05 0:00 /bin/sh -ec ifup --allow=hotplug eno1; ifup --allow=auto eno1; if ifquery eno1
 >/dev/null; then ifquery --state eno1 >/dev/null; fi
root 13787 0.0 0.0 4592 1868 ? S 13:05 0:00 ifup --allow=auto eno1
root 14179 0.0 0.0 4628 772 ? S 13:05 0:00 /bin/sh -c /bin/run-parts --exit-on-error /etc/network/if-up.d
root 14182 0.0 0.0 4520 768 ? S 13:05 0:00 /bin/run-parts --exit-on-error /etc/network/if-up.d
root 14183 0.0 0.0 4628 772 ? S 13:05 0:00 /bin/sh /etc/network/if-up.d/000resolvconf
root 14461 0.0 0.0 4520 752 ? S 13:05 0:00 run-parts --arg=-a --arg=eno1.inet /etc/resolvconf/update.d
root 14479 0.0 0.0 4520 728 ? S 13:05 0:00 run-parts /etc/resolvconf/update-libc.d
root 14503 0.0 0.0 4628 1612 ? S 13:05 0:00 /bin/sh /usr/lib/avahi/avahi-daemon-check-dns.sh
root 14606 0.0 0.0 187532 8384 ? Sl 13:05 0:00 host -t soa local.

(gdb) t a a bt

Thread 4 (Thread 0x7f3231f00700 (LWP 14796)):
#0 0x00007f3237b06bb7 in epoll_wait (epfd=5, events=0x7f3238eb1010, maxevents=64, timeout=timeout@entry=-1)
    at ../sysdeps/unix/sysv/linux/epoll_wait.c:30
#1 0x00007f323804773b in watcher (uap=0x7f3238eb0010) at ../../../../lib/isc/unix/socket.c:4280
#2 0x00007f3237ddd6db in start_thread (arg=0x7f3231f00700) at pthread_create.c:463
#3 0x00007f3237b0688f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 3 (Thread 0x7f3232701700 (LWP 14794)):
#0 0x00007f3237de39f3 in futex_wait_cancelable (private=<optimised out>, expected=0, futex_word=0x7f3238eae0a4)
    at ../sysdeps/unix/sysv/linux/futex-internal.h:88
#1 __pthread_cond_wait_common (abstime=0x0, mutex=0x7f3238eae028, cond=0x7f3238eae078) at pthread_cond_wait.c:502
#2 __pthread_cond_wait (cond=0x7f3238eae078, mutex=mutex@entry=0x7f3238eae028) at pthread_cond_wait.c:655
#3 0x00007f3238039370 in run (uap=0x7f3238eae010) at ../../../lib/isc/timer.c:808
#4 0x00007f3237ddd6db in start_thread (arg=0x7f3232701700) at pthread_create.c:463
#5 0x00007f3237b0688f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 2 (Thread 0x7f3232f02700 (LWP 14791)):
#0 0x00007f3237de39f3 in futex_wait_cancelable (private=<optimised out>, expected=0, futex_word=0x7f3238eac0cc)
    at ../sysdeps/unix/sysv/linux/futex-internal.h:88
#1 __pthread_cond_wait_common (abstime=0x0, mutex=0x7f3238eac028, cond=0x7f3238eac0a0) at pthread_cond_wait.c:502
#2 __pthread_cond_wait (cond=cond@entry=0x7f3238eac0a0, mutex=mutex@entry=0x7f3238eac028) at pthread_cond_wait.c:655
#3 0x00007f32380329e0 in dispatch (manager=0x7f3238eac010) at ../../../lib/isc/task.c:1086
#4 run (uap=0x7f3238eac010) at ../../../lib/isc/task.c:1312
#5 0x00007f3237ddd6db in start_thread (arg=0x7f3232f02700) at pthread_create.c:463
#6 0x00007f3237b0688f in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

Thread 1 (Thread 0x7f3238eeabc0 (LWP 14607)):
#0 0x00007f3237a24236 in __GI___sigsuspend (set=set@entry=0x7ffd71576aa0) at ../sysdeps/unix/sysv/linux/sigsuspend.c:26
#1 0x00007f323803c4d1 in isc__app_ctxrun (ctx0=ctx0@entry=0x7f32382718e0 <isc_g_appctx>) at ../../../../lib/isc/unix/app.c:721
#2 0x00007f323803c7cc in isc__app_run () at ../../../../lib/isc/unix/app.c:754
#3 0x00007f323803d090 in isc_app_run () at ../../../../lib/isc/unix/../app_api.c:198
#4 0x0000563cebce752a in main (argc=4, argv=0x7ffd71576d08) at ../../../bin/dig/host.c:906
(gdb)