如何判断系统是不是处在docker中

可以通过运行命令 `cat /proc/1/cgroup` 查看当前进程所在的 cgroup 路径，如果路径中包含 `/docker` 关键词，则说明该进程运行在 Docker 容器中。例如：

$ cat /proc/1/cgroup
11:blkio:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
10:memory:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
9:hugetlb:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
8:cpuset:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
7:perf_event:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
6:net_prio:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
5:net_cls:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
4:freezer:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
3:devices:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
2:cpu,cpuacct:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef
1:name=systemd:/docker/1234567890abcdef1234567890abcdef1234567890abcdef1234567890abcdef

在上面的输出中，可以看到 `/docker` 出现在每个 cgroup 路径中，因此可以判断系统当前运行在 Docker 容器中。