在将结点注册到master时，出错！

CGROUPS_MEMORY: missing

[preflight] Running pre-flight checks
[WARNING IsDockerSystemdCheck]: detected “cgroupfs” as the Docker cgroup driver. The recommended driver is “systemd”. Please follow the guide at https://kubernetes.io/docs/setup/cri/
[preflight] The system verification failed. Printing the output from the verification:
KERNEL_VERSION: 5.4.0-1025-raspi
CONFIG_NAMESPACES: enabled
CONFIG_NET_NS: enabled
CONFIG_PID_NS: enabled
CONFIG_IPC_NS: enabled
CONFIG_UTS_NS: enabled
CONFIG_CGROUPS: enabled
CONFIG_CGROUP_CPUACCT: enabled
CONFIG_CGROUP_DEVICE: enabled
CONFIG_CGROUP_FREEZER: enabled
CONFIG_CGROUP_SCHED: enabled
CONFIG_CPUSETS: enabled
CONFIG_MEMCG: enabled
CONFIG_INET: enabled
CONFIG_EXT4_FS: enabled
CONFIG_PROC_FS: enabled
CONFIG_NETFILTER_XT_TARGET_REDIRECT: enabled (as module)
CONFIG_NETFILTER_XT_MATCH_COMMENT: enabled (as module)
CONFIG_OVERLAY_FS: enabled (as module)
CONFIG_AUFS_FS: enabled (as module)
CONFIG_BLK_DEV_DM: enabled
DOCKER_VERSION: 18.09.0
DOCKER_GRAPH_DRIVER: overlay2
OS: Linux
CGROUPS_CPU: enabled
CGROUPS_CPUACCT: enabled
CGROUPS_CPUSET: enabled
CGROUPS_DEVICES: enabled
CGROUPS_FREEZER: enabled
CGROUPS_MEMORY: missing

解决办法：

编辑 /boot/cmdline.txt 这个文件，加入下面两句：

cgroup_enable=memory cgroup_memory=1

然后 reboot 重启一下即可。

但是！！！！！！！！！

我的树莓派4B Ubuntu1804 并找不到这个文件，仔细搜索发现，该文件被转移到了/boot/firmware/nobtcmd.txt 中，故只需要在nobtcmd.txt 中加入

cgroup_enable=memory cgroup_memory=1，然后 reboot 重启一下即可。