[Libguestfs] virt-inspector command hung up

Hi, I met a problem when using libguestfs-1.28.1 (centos 7.1) on a virtual machine. Execute virt-inspector command to get OS information and the command hangs . ....................... Launching appliance, timeout set to 600 seconds libguestfs: launch: program=virt-inspcetor libguestfs: launch: version=1.28.1rhel=7,release=1.18.el7,libvirt libguestfs: launch: backend registered: unix libguestfs: launch: backend registered: uml libguestfs: launch: backend registered: libvirt libguestfs: launch: backend registered: direct libguestfs: launch: backend=libvirt libguestfs: launch: tmpdir=/tmp/libguestfsQp28Qo libguestfs: launch: umask=0027 libguestfs: launch: euid=2016 libguestfs: libvirt version = 1002008 (1.2.8) libguestfs: guest random name = guestfs-w8hcve9rhu0dve4a libguestfs: [00000ms] connect to libvirt libguestfs: opening libvirt handle: URI = qemu://session, auth = default+wrapper, flags = 0 command hung on here.We review the libguestfs soure code It seems that libguestfs call libvirt API virConnetOpenAuth failed but no returns. And I set LIBVIRT_DEBUG=debug,and execute virt-inspect command again. I find the command hung after function virFileFindResourceFull from libvirt debug log. ......... 2017-03-11 07:19:09.246+000: 114046: debug: doRemoteOpen:882 : Peoceeding with sockname /run/user/2016/libvirt/libvirt-sock 2017-03-11 07:19:09.246+000: 114046: debug: virFileFindResourceFull:1608 : Resolved 'libvirtd' to ‘/usr/sbin/libvirtd’ there is no more debug log. System run well about half of a year before this problem happened. Any ideas? PS: can I reboot virtual machine to resume it? Thanks Gao Lin