If you run Linux in a VM on Xen, you need to install the kernel and use pygrub (see https://wiki.debian.org/PyGrub) and update to docker version 19.03.0.

install pygrub

1. In your VM execute:

mkdir /boot/grubapt-get install -y linux-image-amd64cat > /boot/grub/menu.lst << EOFdefault         0timeout         2title           Debian GNU/Linuxroot            (hd0,0)kernel          /vmlinuz root=/dev/xvda2 roinitrd          /initrd.imgtitle           Debian GNU/Linux (recovery mode)root            (hd0,0)kernel          /vmlinuz root=/dev/xvda2 ro singleinitrd          /initrd.imgEOF

2. halt your VM, for example:

xen destroy vm01

3. edit your xen config

for example for your VM /etc/xen/vm01.cfg in your DOM0 (comment out the first two lines and add the last three):

#kernel      = '/boot/vmlinuz-4.9.0-9-amd64'#ramdisk     = '/boot/initrd.img-4.9.0-9-amd64'extra       = 'elevator=noop'bootloader  = '/usr/lib/xen-4.8/bin/pygrub'bootloader_args = [ '--kernel=/vmlinuz', '--ramdisk=/initrd.img', ]

4. start your vm:

xen create /etc/xen/vm01.cfg

I have the same problem in a Debian 9 VM and the same in Debian 8 VM both on the same Debian XEN 4.8 host.

loopback seems not to exist:

# losetup -flosetup: cannot find an unused loop device: No such device

You can create those with

#!/bin/bashensure_loop(){  num="$1"  dev="/dev/loop$num"  if test -b "$dev"; then    echo "$dev is a usable loop device."    return 0  fi  echo "Attempting to create $dev for docker ..."  if ! mknod -m660 $dev b 7 $num; then    echo "Failed to create $dev!" 1>&2    return 3  fi  return 0}ensure_loop 0ensure_loop 0

But this is just a tip to find the right solution, it didn't solve it completely, now since /dev/loop0 exists, I have the error:

Error opening loopback device: open /dev/loop0: no such device or address[graphdriver] prior storage driver devicemapper failed: loopback attach failed

Update:

I installed apt-get install docker-ce docker-ce-cli containerd.io like described in the latest docs and now with the latest version:

$ docker --versionDocker version 19.03.0, build aeac9490dc

still the same issue:

failed to start daemon: error initializing graphdriver: loopback attach failed

This is the full log:

level=info msg="Starting up"level=warning msg="failed to rename /var/lib/docker/tmp for background deletion: rename /var/lib/docker/tmp /var/lib/docker/tmp-old: file exists. Deleting synchronously"level=info msg="parsed scheme: \"unix\"" module=grpclevel=info msg="scheme \"unix\" not registered, fallback to default scheme" module=grpclevel=info msg="ccResolverWrapper: sending update to cc: {[{unix:///run/containerd/containerd.sock 0  <nil>}] }" module=grpclevel=info msg="ClientConn switching balancer to \"pick_first\"" module=grpclevel=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc0005e8660, CONNECTING" module=grpclevel=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc0005e8660, READY" module=grpclevel=info msg="parsed scheme: \"unix\"" module=grpclevel=info msg="scheme \"unix\" not registered, fallback to default scheme" module=grpclevel=info msg="ccResolverWrapper: sending update to cc: {[{unix:///run/containerd/containerd.sock 0  <nil>}] }" module=grpclevel=info msg="ClientConn switching balancer to \"pick_first\"" module=grpclevel=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc0007f5b10, CONNECTING" module=grpclevel=info msg="pickfirstBalancer: HandleSubConnStateChange: 0xc0007f5b10, READY" module=grpclevel=error msg="There are no more loopback devices available."level=error msg="[graphdriver] prior storage driver devicemapper failed: loopback attach failed"failed to start daemon: error initializing graphdriver: loopback attach failed

Update 2:

In the end I found out, that pygrub was missing in the VM, which seems to be a new dependency since some version.

This answer was a dead end path, I added another answer, but I leave this here for other users, that have a different problem to get some hints.