OpenWrt has no ss: the listening-socket command fell through to [no-ss]
and the reading raised ListeningSocketsUnavailable. Without ss it now runs
netstat -lntup (busybox and net-tools both), and the cgroups are read for
its PIDs alike.
- netstat names a socket's process as PID/Program; a UDP line has no
state column, "-" is a socket without a process, and net-tools prints
tcp6/udp6 and program names with a space ("sshd: /usr/sbin").
- On OpenWrt the cgroup is /services/<name>/<instance>, so the unit is
the procd service -- a jailed one too, whose PID is not the one procd
reports (dnsmasq under ujail).
- A host with neither tool still raises ListeningSocketsUnavailable.
Checked against a real OpenWrt 25.12.2 access point, and that a Linux and
a Proxmox host still read the same sockets with the longer command.
2.5.0. For netOrk#673.