没有ping工具如何确定机器是否联网

Answer useful for Docker

Ping is ICMP, if you blocked ICMP you can't ping.

You might still be able to test TCP or UDP ports if you are accepting TCP/UDP connections.

If you are running your test on containers, which lack ping, nc, telnet and other tools, you can use this trick:

(echo >/dev/tcp/${host}/${port}) &>/dev/null && echo "open" || echo "closed"

This will attempt to connect through tcp/udp through the device (wow, I know) and echo "open" if the port is open or "closed" if it is closed.

It will hang for a while before echoing "close" when that is the case.

link: https://serverfault.com/questions/13780/how-can-i-determine-if-a-machine-is-online-without-using-ping/923193#923193

nsenter 命令也是也可以实现宿主机的命令调试容器网络.