Some programs might create network namespaces without registering them in /run/netns
as iproute2 does.
This makes it hard to access them with readily available tools like ip netns exec
.
However, there is a way to register those network namespace, after they have been created.
The following session creates and enters an unnamed namespace:
# unshare -n bash
# ip a l
1: lo: mtu 65536 qdisc noop state DOWN group default qlen 1000