How can I migrate an lxc container from Proxmox 6 to Debian 10 ?

[Marc Ballat]

Hi,

I am having difficulties migrating a Debian container running on a Proxmox 6 host (5.4.106-1-pve) to a plain Debian 10 server (kernel 4.19.0-16-amd64).

I tried the following :
- restore from Proxmox backup
- restore from tar archive with --numeric-owner option
- run lxc-start as user and as root, with unprivileged: 0 and unprivileged: 1

Here is one of the log outputs I get (this one is when I run sudo lxc-start) :

lxc-start 100 20210516145622.172 INFO     lsm - lsm/lsm.c:lsm_init:40 - Initialized LSM security driver AppArmor
lxc-start 100 20210516145622.175 DEBUG    terminal - terminal.c:lxc_terminal_peer_default:672 - Using terminal "/dev/tty" as proxy
lxc-start 100 20210516145622.175 DEBUG    terminal - terminal.c:lxc_terminal_winsz:61 - Set window size to 265 columns and 47 rows
lxc-start 100 20210516145622.178 INFO     start - start.c:lxc_init:837 - Container "100" is initialized
lxc-start 100 20210516145622.178 WARN     cgfsng - cgroups/cgfsng.c:cgroup_tree_create:1168 - Success - The /sys/fs/cgroup/freezer//lxc.monitor.100 cgroup already existed
lxc-start 100 20210516145622.178 DEBUG    cgfsng - cgroups/cgfsng.c:cgfsng_monitor_create:1355 - Failed to create cgroup "(null)"
lxc-start 100 20210516145622.180 WARN     cgfsng - cgroups/cgfsng.c:mkdir_eexist_on_last:1152 - File exists - Failed to create directory "/sys/fs/cgroup/cpuset//lxc.monitor.100
-1"
lxc-start 100 20210516145622.182 INFO     cgfsng - cgroups/cgfsng.c:cgfsng_monitor_create:1368 - The monitor process uses "lxc.monitor.100-1" as cgroup
lxc-start 100 20210516145622.182 WARN     cgfsng - cgroups/cgfsng.c:cgroup_tree_create:1168 - File exists - The /sys/fs/cgroup/freezer//lxc.payload.100 cgroup already existed
lxc-start 100 20210516145622.182 DEBUG    cgfsng - cgroups/cgfsng.c:cgfsng_payload_create:1458 - Failed to create cgroup "(null)"
lxc-start 100 20210516145622.184 WARN     cgfsng - cgroups/cgfsng.c:mkdir_eexist_on_last:1152 - File exists - Failed to create directory "/sys/fs/cgroup/cpuset//lxc.payload.100
-1"
lxc-start 100 20210516145622.186 INFO     cgfsng - cgroups/cgfsng.c:cgfsng_payload_create:1471 - The container process uses "lxc.payload.100-1" as cgroup
lxc-start 100 20210516145622.191 ERROR    utils - utils.c:lxc_can_use_pidfd:1853 - Kernel does not support pidfds
lxc-start 100 20210516145622.192 INFO     start - start.c:lxc_spawn:1700 - Cloned CLONE_NEWNS
lxc-start 100 20210516145622.192 INFO     start - start.c:lxc_spawn:1700 - Cloned CLONE_NEWPID
lxc-start 100 20210516145622.192 INFO     start - start.c:lxc_spawn:1700 - Cloned CLONE_NEWUTS
lxc-start 100 20210516145622.192 INFO     start - start.c:lxc_spawn:1700 - Cloned CLONE_NEWIPC
lxc-start 100 20210516145622.192 INFO     start - start.c:lxc_spawn:1700 - Cloned CLONE_NEWNET
lxc-start 100 20210516145622.192 DEBUG    start - start.c:lxc_try_preserve_namespaces:167 - Preserved mnt namespace via fd 35
lxc-start 100 20210516145622.192 DEBUG    start - start.c:lxc_try_preserve_namespaces:167 - Preserved pid namespace via fd 36
lxc-start 100 20210516145622.193 DEBUG    start - start.c:lxc_try_preserve_namespaces:167 - Preserved uts namespace via fd 37
lxc-start 100 20210516145622.193 DEBUG    start - start.c:lxc_try_preserve_namespaces:167 - Preserved ipc namespace via fd 38
lxc-start 100 20210516145622.193 DEBUG    start - start.c:lxc_try_preserve_namespaces:167 - Preserved net namespace via fd 39
lxc-start 100 20210516145622.198 INFO     start - start.c:do_start:1198 - Unshared CLONE_NEWCGROUP
lxc-start 100 20210516145622.200 ERROR    conf - conf.c:lxc_mount_rootfs:1234 - Permission denied - Failed to recursively turn root mount tree into dependent mount
lxc-start 100 20210516145622.200 ERROR    conf - conf.c:lxc_setup_rootfs_prepare_root:3142 - Failed to setup rootfs for
lxc-start 100 20210516145622.200 ERROR    conf - conf.c:lxc_setup:3278 - Failed to setup rootfs
lxc-start 100 20210516145622.201 ERROR    start - start.c:do_start:1218 - Failed to setup container "100"
lxc-start 100 20210516145622.201 ERROR    sync - sync.c:__sync_wait:36 - An error occurred in another process (expected sequence number 5)
lxc-start 100 20210516145622.202 DEBUG    network - network.c:lxc_delete_network:3672 - Deleted network devices
lxc-start 100 20210516145622.203 ERROR    start - start.c:__lxc_start:1999 - Failed to spawn container "100"
lxc-start 100 20210516145622.203 WARN     start - start.c:lxc_abort:1018 - No such process - Failed to send SIGKILL to 883
lxc-start 100 20210516145622.690 ERROR    lxc_start - tools/lxc_start.c:main:308 - The container failed to start

I can't find what's wrong...