Solution for problem: rootless Docker container cannot ping outside networks

I am running a rootless docker container on a Ubuntu host (24.04 LTS). However, I cannot ping the host where the container is running and the outside network. The workaround I created are two steps:

1. Run the container with the --privileged option, as in

   docker container run --privileged 

2. On the host where the container is running, set Linux kernel parameber `net.ipv4.ping_group_range` to include the group id that runs the container. For instance, if the group id of the user that runs the container is 3000, we can set the parameter as follows:

   echo "3000 3000" > /proc/sys/net/ipv4/ping_group_range

If tests indicate that pings are successful in the container, we can set the kernel parameter through a configuration file so that the setting can survive reboot, e.g.,

• On the host that the container is running, create a file, e.g., /etc/sysctl.d/99-ping-group-range.conf as in:

  echo "net.ipv4.ping_group_range=3000 3000" \
         > /etc/sysctl.d/99-ping-group-range.conf

The idea of these is from

1. https://github.com/containers/podman/issues/2488
2. https://opennms.discourse.group/t/how-to-allow-unprivileged-users-to-use-icmp-ping/1573