[Libguestfs] guestfs_launch() fails when C application is started as a systemd service

Peter Dimitrov peterd at telco.com
Wed Nov 7 10:32:48 UTC 2018

Thank you, Rich,
This was the issue indeed. export LIBGUESTFS_BACKEND=direct fixed it.

The next step I tried was to integrate libguestfs in collectd virt plugin
to collect this data automatically.
In this case I'm having an unknown error in add_libvirt_dom() (same with
add_domain) when it's invoking qemu-img to create overlay image.

There is no difference between manual and service execution.
I tried setting LIBGUESTFS_BACKEND to direct,
libvirt, libvirt:qemu:///session with no success.
Also tried using a different tmp dir just in case - nothing.

Maybe something is wrong with how collectd runs its plugins (dynamic
Invoking virt-df from collectd's plugin gives the same error message.
I tried running the same qemu-img command from collectd and it passes
though! Confusing...

Do you have any hints what to try?

Here is the complete output from collectd:

[2018-11-07 12:21:54] plugin_load: plugin "logfile" successfully loaded.
[2018-11-07 12:21:54] plugin_load: plugin "syslog" successfully loaded.
Before guestfs_create()
UID: 0
Effective UID: 0
Before guestfs_set_verbose()
Before guestfs_set_trace()
Before guestfs_add_domain()
libguestfs: trace: add_domain "wer" "readonly:true"
libguestfs: opening libvirt handle: URI = NULL, auth = default+wrapper,
flags = 0
libguestfs: successfully opened libvirt handle: conn = 0x7f7e70005210
libguestfs: trace: add_libvirt_dom (virDomainPtr)0x7f7e70005fa0
libguestfs: original domain XML:\n<domain type='kvm' id='9'>\n
<name>wer</name>\n  <uuid>03fde334-92a5-4e5e-9247-924c9d40230f</uuid>\n
<memory unit='KiB'>2097152</memory>\n  <currentMemory
unit='KiB'>2097152</currentMemory>\n  <vcpu placement='static'>1</vcpu>\n
<resource>\n    <partition>/machine</partition>\n  </resource>\n  <os>\n
<type arch='x86_64' machine='pc-i440fx-2.7'>hvm</type>\n    <bootmenu
enable='yes'/>\n  </os>\n  <features>\n    <acpi/>\n    <apic/>\n
<vmport state='off'/>\n  </features>\n  <cpu mode='custom'
match='exact'>\n    <model fallback='allow'>Westmere</model>\n  </cpu>\n
<clock offset='utc'>\n    <timer name='rtc' tickpolicy='catchup'/>\n
<timer name='pit' tickpolicy='delay'/>\n    <timer name='hpet'
present='no'/>\n  </clock>\n  <on_poweroff>destroy</on_poweroff>\n
<on_reboot>restart</on_reboot>\n  <on_crash>destroy</on_crash>\n  <pm>\n
<suspend-to-mem enabled='no'/>\n    <suspend-to-disk enabled='no'/>\n
</pm>\n  <devices>\n    <emulator>/usr/bin/qemu-kvm</emulator>\n    <disk
type='file' device='disk'>\n      <driver name='qemu' type='qcow2'/>\n
<source file='/home/peterd/TVE/wer.qcow2'/>\n      <backingStore/>\n
<target dev='sda' bus='sata'/>\n      <boot order='1'/>\n      <alias
name='sata0-0-0'/>\n      <address type='drive' controller='0' bus='0'
target='0' unit='0'/>\n    </disk>\n    <disk type='file' device='disk'>\n
    <driver name='qemu' type='qcow2'/>\n      <source
file='/var/lib/libvirt/images/wer.qcow2'/>\n      <backingStore/>\n
<target dev='sdb' bus='sata'/>\n      <alias name='sata0-0-1'/>\n
<address type='drive' controller='0' bus='0' target='0' unit='1'/>\n
</disk>\n    <disk type='file' device='cdrom'>\n      <driver name='qemu'
type='raw'/>\n      <source file='/home/peterd/boot_new.iso'/>\n
<backingStore/>\n      <target dev='hda' bus='ide'/>\n      <readonly/>\n
    <boot order='2'/>\n      <alias name='ide0-0-0'/>\n      <address
type='drive' controller='0' bus='0' target='0' unit='0'/>\n    </disk>\n
<controller type='usb' index='0' model='ich9-ehci1'>\n      <alias
name='usb'/>\n      <address type='pci' domain='0x0000' bus='0x00'
slot='0x06' function='0x7'/>\n    </controller>\n    <controller type='usb'
index='0' model='ich9-uhci1'>\n      <alias name='usb'/>\n      <master
startport='0'/>\n      <address type='pci' domain='0x0000' bus='0x00'
slot='0x06' function='0x0' multifunction='on'/>\n    </controller>\n
<controller type='usb' index='0' model='ich9-uhci2'>\n      <alias
name='usb'/>\n      <master startport='2'/>\n      <address type='pci'
domain='0x0000' bus='0x00' slot='0x06' function='0x1'/>\n
</controller>\n    <controller type='usb' index='0' model='ich9-uhci3'>\n
    <alias name='usb'/>\n      <master startport='4'/>\n      <address
type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x2'/>\n
</controller>\n    <controller type='ide' index='0'>\n      <alias
name='ide'/>\n      <address type='pci' domain='0x0000' bus='0x00'
slot='0x01' function='0x1'/>\n    </controller>\n    <controller
type='sata' index='0'>\n      <alias name='sata0'/>\n      <address
type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>\n
</controller>\n    <controller type='virtio-serial' index='0'>\n
<alias name='virtio-serial0'/>\n      <address type='pci' domain='0x0000'
bus='0x00' slot='0x07' function='0x0'/>\n    </controller>\n    <controller
type='scsi' index='0' model='virtio-scsi'>\n      <alias name='scsi0'/>\n
    <address type='pci' domain='0x0000' bus='0x00' slot='0x09'
function='0x0'/>\n    </controller>\n    <controller type='pci' index='0'
model='pci-root'>\n      <alias name='pci.0'/>\n    </controller>\n
<interface type='direct'>\n      <mac address='52:54:00:2c:7a:bf'/>\n
<source dev='macvlan0' mode='bridge'/>\n      <target dev='macvtap0'/>\n
  <model type='e1000'/>\n      <alias name='net0'/>\n      <address
type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>\n
</interface>\n    <serial type='pty'>\n      <source path='/dev/pts/8'/>\n
    <target port='0'/>\n      <alias name='serial0'/>\n    </serial>\n
<console type='pty' tty='/dev/pts/8'>\n      <source path='/dev/pts/8'/>\n
    <target type='serial' port='0'/>\n      <alias name='serial0'/>\n
</console>\n    <channel type='spicevmc'>\n      <target type='virtio'
name='com.redhat.spice.0' state='disconnected'/>\n      <alias
name='channel0'/>\n      <address type='virtio-serial' controller='0'
bus='0' port='1'/>\n    </channel>\n    <input type='mouse' bus='ps2'>\n
  <alias name='input0'/>\n    </input>\n    <input type='keyboard'
bus='ps2'>\n      <alias name='input1'/>\n    </input>\n    <graphics
type='spice' port='5900' autoport='yes' listen=''>\n      <listen
type='address' address=''/>\n      <image compression='off'/>\n
</graphics>\n    <sound model='ich6'>\n      <alias name='sound0'/>\n
<address type='pci' domain='0x0000' bus='0x00' slot='0x04'
function='0x0'/>\n    </sound>\n    <video>\n      <model type='qxl'
ram='65536' vram='65536' vgamem='16384' heads='1' primary='yes'/>\n
<alias name='video0'/>\n      <address type='pci' domain='0x0000'
bus='0x00' slot='0x02' function='0x0'/>\n    </video>\n    <redirdev
bus='usb' type='spicevmc'>\n      <alias name='redir0'/>\n      <address
type='usb' bus='0' port='1'/>\n    </redirdev>\n    <redirdev bus='usb'
type='spicevmc'>\n      <alias name='redir1'/>\n      <address type='usb'
bus='0' port='2'/>\n    </redirdev>\n    <memballoon model='virtio'>\n
<alias name='balloon0'/>\n      <address type='pci' domain='0x0000'
bus='0x00' slot='0x08' function='0x0'/>\n    </memballoon>\n  </devices>\n
<seclabel type='none' model='none'/>\n  <seclabel type='dynamic'
model='dac' relabel='yes'>\n    <label>+0:+0</label>\n
<imagelabel>+0:+0</imagelabel>\n  </seclabel>\n</domain>\n
libguestfs: trace: clear_backend_setting "internal_libvirt_norelabel_disks"
libguestfs: trace: clear_backend_setting = 0
libguestfs: disk[0]: filename: /home/peterd/TVE/wer.qcow2
libguestfs: trace: add_drive "/home/peterd/TVE/wer.qcow2" "readonly:true"
libguestfs: creating COW overlay to protect original drive content
libguestfs: trace: get_tmpdir
libguestfs: trace: get_tmpdir = "/tmp"
libguestfs: trace: disk_create "/tmp/libguestfsUIZbDK/overlay1.qcow2"
"qcow2" -1 "backingfile:/home/peterd/TVE/wer.qcow2" "backingformat:qcow2"
libguestfs: command: run: qemu-img
libguestfs: command: run: \ create
libguestfs: command: run: \ -f qcow2
libguestfs: command: run: \ -o
libguestfs: command: run: \ /tmp/libguestfsUIZbDK/overlay1.qcow2
Formatting '/tmp/libguestfsUIZbDK/overlay1.qcow2', fmt=qcow2
size=107374182400 backing_file=/home/peterd/TVE/wer.qcow2 backing_fmt=qcow2
encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16
libguestfs: error: command: waitpid: No child processes
libguestfs: error: qemu-img: /tmp/libguestfsUIZbDK/overlay1.qcow2: qemu-img
exited for an unknown reason (status -1), see debug messages above
libguestfs: trace: disk_create = -1 (error)
libguestfs: trace: add_drive = -1 (error)
libguestfs: trace: add_libvirt_dom = -1 (error)
libguestfs: trace: add_domain = -1 (error)
libguestfs: trace: close
libguestfs: closing guestfs handle 0x7f7e700049f0 (state 0)
libguestfs: command: run: rm
libguestfs: command: run: \ -rf /tmp/libguestfsUIZbDK
libguestfs: error: command: waitpid: No child processes

Best Regards,

On Fri, Nov 2, 2018 at 9:48 PM Richard W.M. Jones <rjones at redhat.com> wrote:

> On Fri, Nov 02, 2018 at 06:04:08PM +0200, Peter Dimitrov wrote:
> > Hello,
> >
> > I have a simple C program that uses libguestfs to extract info about disk
> > usage from a libvirt domain. It works when ran manually as root, but
> fails
> > when started as a systemd service.
> >
> > I'm attaching the service file, source code and verbose logs from both
> the
> > successful manual run and from the service journal.
> >
> > SELinix is disabled.
> >
> > Error messages:
> > libguestfs: set_socket_create_context: getcon failed: (none): Invalid
> > argument [you can ignore this message if you are not using SELinux +
> sVirt]
> > libguestfs: clear_socket_create_context: setsockcreatecon failed: NULL:
> > Invalid argument [you can ignore this message if you are not using
> SELinux
> > + sVirt]
> > libguestfs: error: chown: /tmp/libguestfsvMMaec/guestfsd.sock: Operation
> > not permitted
> > libguestfs: clear_socket_create_context: setsockcreatecon failed: NULL:
> > Invalid argument [you can ignore this message if you are not using
> SELinux
> > + sVirt]
> > libguestfs: trace: launch = -1 (error)
> > failed to launch domain: Invalid argument
> I cannot see what the problem is immediately, but I guess that systemd
> is confining the service in such a way that libvirt has problems.
> Firstly I would try using the direct backend:
>   export LIBGUESTFS_BACKEND=direct
> If it's still not fixed, then it's something to do with systemd
> confining affecting qemu.
> If that fixes it, then it's a problem with libvirt, and you will need
> to find the libvirt log file.  Usually that's in
> /var/log/libvirt/qemu/guestfs-*.log or in
> $HOME/.cache/libvirt/qemu/log/guestfs-*.log  But I've no idea where it
> will end up when you're running everything under systemd.
> Rich.
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
> virt-p2v converts physical machines to virtual machines.  Boot with a
> live CD or over the network (PXE) and turn machines into KVM guests.
> http://libguestfs.org/virt-v2v
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