Description of problem: Fedora 31 and newer uses the unfied cgroup hierarchy. LXC (Linux Container) needs special container config on Fedora 31 and newer. These three trick (written below) should be explained at https://fedoraproject.org/wiki/LXC and possibly pages under https://fedoraproject.org/wiki/Category:Common_bugs Version-Release number of selected component (if applicable): How reproducible: [Item A] On Fedora 31 and newer, a user needs to add lxc.cgroup.devices.allow = lxc.cgroup.devices.deny = to an LXC container config file. Otherwise he or she gets error message ERROR cgfsng - cgroups/cgfsng.c:cg_legacy_set_data:2415 - Failed to setup limits for the "devices" controller. The controller seems to be unused by "cgfsng" cgroup driver or not enabled on the cgroup hierarchy ERROR start - start.c:lxc_spawn:1910 - Failed to setup legacy device cgroup controller limits [Item B] In addition, if /sbin/init is systemd with hybrid cgroup hierarchy as its default hierarchy, the user needs to add lxc.init.cmd = /sbin/init systemd.unified_cgroup_hierarchy=1 Otherwise she or he gets the error message Failed to mount cgroup at /sys/fs/cgroup/systemd: Operation not permitted [!!!!!!] Failed to mount API filesystems. Exiting PID 1... [Item C] The above applies to a privileged LXC container started by root. When a non-root user start an unprivileged container, he or she needs to run lxc-start as systemd-run --user --scope -p "Delegate=yes" lxc-start -F ... otherwise he or she gets the error message $ lxc-start -F -n nonroot-fedora31 lxc-start: nonroot-fedora31: cgroups/cgfsng.c: mkdir_eexist_on_last: 1279 Permission denied - Failed to create directory "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: monitor_create_path_for_hierarchy: 1300 Failed to create cgroup "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/nonroot-fedora31" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: cgfsng_monitor_create: 1389 Failed to create cgroup "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/nonroot-fedora31" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: mkdir_eexist_on_last: 1279 Permission denied - Failed to create directory "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: monitor_create_path_for_hierarchy: 1300 Failed to create cgroup "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/nonroot-fedora31-1" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: cgfsng_monitor_create: 1389 Failed to create cgroup "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/nonroot-fedora31-1" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: mkdir_eexist_on_last: 1279 Permission denied - Failed to create directory "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: monitor_create_path_for_hierarchy: 1300 Failed to create cgroup "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/nonroot-fedora31-2" lxc-start: nonroot-fedora31: cgroups/cgfsng.c: cgfsng_monitor_create: 1389 Failed to create cgroup "/sys/fs/cgroup/user.slice/user-1000.slice/session-2.scope/lxc.monitor/nonroot-fedora31-2" Steps to Reproduce: 1. dnf install lxc lxc-templates on Fedora 31 or newer 2. lxc-create -n fedora31 -t download -- -d fedora -r 31 -a amd64 3. lxc-start -F -n fedora31 Actual results: There is no instruction for users to start an LXC container on Fedora 31 and newer. Expected results: There is some friendly documentation and Fedora users do not suffer from lack of documantation. Additional info: Related bug reports against the LXC fedora package bugs 1765821, 1787093, 1787097
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