重新启动后，libvirtd拒绝开始使用 systemv，且不产生任何有用的错误：
systemctl status libvirtd.service
● libvirtd.service - Virtualization daemon
Loaded: loaded (/lib/systemd/system/libvirtd.service; enabled)
Active: failed (Result: start-limit) since Mon 2016-11-28 17:03:16 GMT; 1min 6s ago
Docs: man:libvirtd(8)
http://libvirt.org
Process: 8295 ExecStart=/usr/sbin/libvirtd $libvirtd_opts (code=exited, status=1/FAILURE)
Main PID: 8295 (code=exited, status=1/FAILURE)
Nov 28 17:03:16 localhost systemd[1]: Failed to start Virtualization daemon.
Nov 28 17:03:16 localhost systemd[1]: Unit libvirtd.service entered failed state.
Nov 28 17:03:16 localhost systemd[1]: libvirtd.service holdoff time over, scheduling restart.
Nov 28 17:03:16 localhost systemd[1]: Stopping Virtualization daemon...
Nov 28 17:03:16 localhost systemd[1]: Starting Virtualization daemon...
Nov 28 17:03:16 localhost systemd[1]: libvirtd.service start request repeated too quickly, refusing to start.
Nov 28 17:03:16 localhost systemd[1]: Failed to start Virtualization daemon.
Nov 28 17:03:16 localhost systemd[1]: Unit libvirtd.service entered failed state.
尝试使用journalctl来获取输出：
journalctl -xn
-- Logs begin at Mon 2016-11-28 16:02:48 GMT, end at Mon 2016-11-28 17:03:16 GMT. --
Nov 28 17:03:16 localhost libvirtd[8295]: /usr/sbin/libvirtd: initialization failed
Nov 28 17:03:16 localhost systemd[1]: libvirtd.service: main process exited, code=exited, status=1/FAILURE
Nov 28 17:03:16 localhost systemd[1]: Failed to start Virtualization daemon.
-- Subject: Unit libvirtd.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit libvirtd.service has failed.
--
-- The result is failed.
Nov 28 17:03:16 localhost systemd[1]: Unit libvirtd.service entered failed state.
Nov 28 17:03:16 localhost systemd[1]: libvirtd.service holdoff time over, scheduling restart.
Nov 28 17:03:16 localhost systemd[1]: Stopping Virtualization daemon...
-- Subject: Unit libvirtd.service has begun shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit libvirtd.service has begun shutting down.
Nov 28 17:03:16 localhost systemd[1]: Starting Virtualization daemon...
-- Subject: Unit libvirtd.service has begun with start-up
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit libvirtd.service has begun starting up.
Nov 28 17:03:16 localhost systemd[1]: libvirtd.service start request repeated too quickly, refusing to start.
Nov 28 17:03:16 localhost systemd[1]: Failed to start Virtualization daemon.
-- Subject: Unit libvirtd.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
--
-- Unit libvirtd.service has failed.
--
-- The result is failed.
也没什么帮助。有趣的是，当我直接执行守护进程时，它运行起来没有错误或警告，而且[info]没有任何问题！
- 我怎样才能找出导致此现象的原因？
- 我如何才能找出导致服务失败但直接守护进程成功的原因？
__编辑__
我已按照journalctl -u libvirtd.service -b建议尝试过：
Nov 28 16:03:00 localhost systemd[1]: Starting Virtualization daemon...
Nov 28 16:03:01 localhost libvirtd[1090]: /usr/sbin/libvirtd: initialization failed
Nov 28 16:03:01 localhost systemd[1]: libvirtd.service: main process exited, code=exited, status=1/FAILURE
Nov 28 16:03:01 localhost systemd[1]: Failed to start Virtualization daemon.
Nov 28 16:03:01 localhost systemd[1]: Unit libvirtd.service entered failed state.
Nov 28 16:03:01 localhost systemd[1]: libvirtd.service holdoff time over, scheduling restart.
Nov 28 16:03:01 localhost systemd[1]: Stopping Virtualization daemon...
Nov 28 16:03:01 localhost systemd[1]: Starting Virtualization daemon...
Nov 28 16:03:01 localhost libvirtd[1167]: /usr/sbin/libvirtd: initialization failed
Nov 28 16:03:01 localhost systemd[1]: libvirtd.service: main process exited, code=exited, status=1/FAILURE
Nov 28 16:03:01 localhost systemd[1]: Failed to start Virtualization daemon.
Nov 28 16:03:01 localhost systemd[1]: Unit libvirtd.service entered failed state.
Nov 28 16:03:01 localhost systemd[1]: libvirtd.service holdoff time over, scheduling restart.
Nov 28 16:03:01 localhost systemd[1]: Stopping Virtualization daemon...
Nov 28 16:03:01 localhost systemd[1]: Starting Virtualization daemon...
但输出并没有什么帮助，它只指出守护进程没有启动，但没有指出失败原因的详细信息。