mirror of
https://gitlab.com/libvirt/libvirt.git
synced 2024-11-05 12:51:12 +00:00
0c99ef5b05
Signed-off-by: Tim Wiederhake <twiederh@redhat.com> Reviewed-by: Peter Krempa <pkrempa@redhat.com>
130 lines
5.5 KiB
ReStructuredText
130 lines
5.5 KiB
ReStructuredText
=============================
|
|
Capturing core dumps for QEMU
|
|
=============================
|
|
|
|
The default behaviour for a QEMU virtual machine launched by libvirt is to
|
|
have core dumps disabled. There can be times, however, when it is beneficial
|
|
to collect a core dump to enable debugging.
|
|
|
|
QEMU driver configuration
|
|
=========================
|
|
|
|
There is a global setting in the QEMU driver configuration file that controls
|
|
whether core dumps are permitted, and their maximum size. Enabling core dumps
|
|
is simply a matter of setting the maximum size to a non-zero value by editing
|
|
the ``/etc/libvirt/qemu.conf`` file:
|
|
|
|
::
|
|
|
|
max_core = "unlimited"
|
|
|
|
For an adhoc debugging session, setting the core dump size to "unlimited" is
|
|
viable, on the assumption that core dumps will be disabled again once the
|
|
requisite information is collected. If the intention is to leave core dumps
|
|
permanently enabled, more careful consideration of limits is required
|
|
|
|
Note that by default, a core dump will **NOT** include the guest RAM
|
|
region, only memory regions used by QEMU for emulation and backend purposes.
|
|
This is expected to be sufficient for the vast majority of debugging needs.
|
|
|
|
When there is a need to examine guest RAM though, a further setting is
|
|
available:
|
|
|
|
::
|
|
|
|
dump_guest_core = 1
|
|
|
|
This will of course result in core dumps that are as large as the biggest
|
|
virtual machine on the host - potentially 10's or even 100's of GB in size.
|
|
|
|
After changing either of the settings in ``/etc/libvirt/qemu.conf`` the daemon
|
|
hosting the QEMU driver must be restarted. For deployments using the monolithic
|
|
daemons, this means ``libvirtd``, while for those using modular daemons this
|
|
means ``virtqemud``:
|
|
|
|
::
|
|
|
|
systemctl restart libvirtd (for a monolithic deployment)
|
|
systemctl restart virtqemud (for a modular deployment)
|
|
|
|
While libvirt attempts to make it possible to restart the daemons without
|
|
negatively impacting running guests, there are some management operations
|
|
that may get interrupted. In particular long running jobs like live
|
|
migration or block device copy jobs may abort. It is thus wise to check
|
|
that the host is mostly idle before restarting the daemons.
|
|
|
|
Guest core dump configuration
|
|
=============================
|
|
|
|
The ``dump_guest_core`` setting mentioned above will allow guest RAM to be
|
|
included in core dumps for all virtual machines on the host. This may not
|
|
be desirable, so it is also possible to control this on a per-virtual
|
|
machine basis in the XML configuration:
|
|
|
|
::
|
|
|
|
<memory dumpCore="on">...</memory>
|
|
|
|
Note, it is still necessary to at least set ``max_core`` to a non-zero
|
|
value in the global configuration file.
|
|
|
|
Some management applications may not offer the ability to customimze the
|
|
XML configuration for a guest. In such situations, using the global
|
|
``dump_guest_core`` setting is the only option.
|
|
|
|
Host OS core dump storage
|
|
=========================
|
|
|
|
The Linux kernel default behaviour is to write core dumps to a file in the
|
|
current working directory of the process. This will not work with QEMU
|
|
processes launched by libvirt, because their working directory is ``/``
|
|
which will not be writable.
|
|
|
|
Most modern OS distros, however, now include systemd which configures a
|
|
custom core dump handler out of the box. When this is in effect, core dumps
|
|
from QEMU can be seen using the ``coredumpctl`` commands:
|
|
|
|
::
|
|
|
|
$ coredumpctl list -r
|
|
TIME PID UID GID SIG COREFILE EXE SIZE
|
|
Tue 2021-07-20 12:12:52 BST 2649303 107 107 SIGABRT present /usr/bin/qemu-system-x86_64 1.8M
|
|
...snip...
|
|
|
|
$ coredumpctl info 2649303
|
|
PID: 2649303 (qemu-system-x86)
|
|
UID: 107 (qemu)
|
|
GID: 107 (qemu)
|
|
Signal: 6 (ABRT)
|
|
Timestamp: Tue 2021-07-20 12:12:52 BST (48min ago)
|
|
Command Line: /usr/bin/qemu-system-x86_64 -name guest=f30,debug-threads=on ..snip... -msg timestamp=on
|
|
Executable: /usr/bin/qemu-system-x86_64
|
|
Control Group: /machine.slice/machine-qemu\x2d1\x2df30.scope/libvirt/emulator
|
|
Unit: machine-qemu\x2d1\x2df30.scope
|
|
Slice: machine.slice
|
|
Boot ID: 6b9015d0c05f4e7fbfe4197a2c7824a2
|
|
Machine ID: c78c8286d6d74b22ac0dd275975f9ced
|
|
Hostname: localhost.localdomain
|
|
Storage: /var/lib/systemd/coredump/core.qemu-system-x86.107.6b9015d0c05f4e7fbfe4197a2c7824a2.2649303.1626779572000000.zst (present)
|
|
Disk Size: 1.8M
|
|
Message: Process 2649303 (qemu-system-x86) of user 107 dumped core.
|
|
|
|
Stack trace of thread 2649303:
|
|
#0 0x00007ff3c32436be n/a (libc.so.6 + 0xf56be)
|
|
#1 0x000055a949c0ed05 qemu_poll_ns (qemu-system-x86_64 + 0x7b0d05)
|
|
#2 0x000055a949c0e476 main_loop_wait (qemu-system-x86_64 + 0x7b0476)
|
|
#3 0x000055a949a36d27 qemu_main_loop (qemu-system-x86_64 + 0x5d8d27)
|
|
#4 0x000055a94979e4d2 main (qemu-system-x86_64 + 0x3404d2)
|
|
#5 0x00007ff3c3175b75 n/a (libc.so.6 + 0x27b75)
|
|
#6 0x000055a9497a1f5e _start (qemu-system-x86_64 + 0x343f5e)
|
|
|
|
Stack trace of thread 2649368:
|
|
#0 0x00007ff3c32435bf n/a (libc.so.6 + 0xf55bf)
|
|
#1 0x00007ff3c3af547c g_main_context_iterate.constprop.0 (libglib-2.0.so.0 + 0xa947c)
|
|
#2 0x00007ff3c3aa0a93 g_main_loop_run (libglib-2.0.so.0 + 0x54a93)
|
|
#3 0x00007ff3c17a727a red_worker_main.lto_priv.0 (libspice-server.so.1 + 0x5227a)
|
|
#4 0x00007ff3c3326299 start_thread (libpthread.so.0 + 0x9299)
|
|
#5 0x00007ff3c324e353 n/a (libc.so.6 + 0x100353)
|
|
|
|
...snip...
|