Basic ethernet setup with minibase

February 08, 2019 — BarryK

I posted a couple of days ago about minibase, created by Alex Suykov:

http://bkhome.org/news/201902/minibase-super-tiny-static-system.html

Since then, I have been learning how it works, and posting questions:

...to which he has patiently and helpfully replied.

Initially, I have explored ethernet network connection, as this is one of the areas in EasyOS (and Quirky and Puppy) that has issues. When I introduced NetworkManager to EasyOS, the ethernet connection problems went away. Basically, NetworkManager automatically detects which ethernet interface is "alive" and connected to a router/modem, and you can turn off the router, turn it back on, change cable to a different ethernet socket on the PC, and NetworkManager automatically adjusts.

I think that Puppy Forum member Jemimah originally created Frisbee network manager with this kind of flexibility in mind (project now maintained by rerwin), but I don't know to what extent that flexibility was achieved.

Anyway, fast-forward to now, testing minibase, and yippee, it has the same automatic flexibility as NetworkManager. Note, NetworkManager is no longer in Easy, as posted yesterday, I removed it:

http://bkhome.org/news/201902/networkmanager-removed-from-easyos.html

The rest of this post will be a mini-tutorial, explaining how I have setup minibase, or rather, just the utilities concerned with ethernet networking. There are these networking utilites, in /sbin:

dhcp  ifctl  ifmon  ip4addr  ip4info  wifi  wsupp

Actually, Alex places 'ifmon' and 'wsupp' in /sbin/service. 'wifi' and 'wsupp' are for wifi, so will leave those out of the discussion for now. Note, the total size of these utilities is 100KB and they are statically-linked.

'ifmon' is a daemon, that is intended to be started at bootup. To easily show output, I have started it in a terminal. I deliberately left the network cable unplugged:

# mkdir /run/ctrl
# ifmon
+++ identify eth0
+++ identify eth1
+++ identify wlan0
+++ mode-lan0 eth0
+++ mode-lan1 eth1

I then plugged in the network cable (between PC and router):

+++ conf-request eth0
+++ dhcp-gw 192.168.1.1
+++ dhcp-dns 192.168.43.1 168.126.63.2

Unplugged the cable:

+++ conf-cancel eth0

Plugged it in again:

+++ conf-request eth0
+++ dhcp-gw 192.168.1.1
+++ dhcp-dns 192.168.43.1 168.126.63.2

The network connection went up when I plugged in the cable, down, then back up when I replugged the cable. The network_tray icon faithfully showed the status.

Technical note:
"aliveness" detection is not done by a polling loop. It is done efficiently by a netlink socket, waiting on notifications from the kernel.

This is great, exactly what I want. Now, some explanation about the messages that 'ifmon' puts out. 'ifmon' relies upon scripts to do any real action. Those scripts are in /etc/net:

conf-cancel  conf-request  dhcp-gw   identify  mode-wifi
conf-renew   dhcp-dns      dhcp-ntp  mode-lan  wifi-wpa

At startup, 'ifmon' calls /etc/net/identify, for each interface that it discovers, passing the interface name, as you can see above. This is what I put into 'identify':

#!/bin/sh
echo "+++ identify $1"
IF="$1"

IDflg=""; NET='lan'
[ -d /sys/class/net/${IF}/wireless ] && NET='wifi'

#test if id already assigned...
[ -s /var/local/interfaces ] && IDflg="$(ifctl | grep "${IF}: ${NET}")"
#if not, assign it...
if [ ! "$IDflg" ];then
 NUM="${IF/*[a-z]/}"
 if [ ! -f /etc/net/mode-${NET}${NUM} ];then
  cp -a /etc/net/mode-${NET} /etc/net/mode-${NET}${NUM}
  sed -i -e "s%\+\+\+ mode-${NET} %+++ mode-${NET}${NUM} %" /etc/net/mode-${NET}${NUM}
 fi
 ifctl ${IF} mode ${NET}${NUM}
fi

ifctl $IF identify

I won't spend much time explaining this. Minibase determines a persistent name for the interface, independent whether the actual interface name "eth0", "eth1" or whatever, changes. This persistent name is assigned to a script. What I have done in the above script is assign eth0 to script /etc/net/mode-lan0 --which will get called even if the name assigned to that interface changes. In other words, script 'mode-lan0' is locked to that physical interface.

Technical note:
"eth0", "eth1" etc., are the names assigned by the linux kernel. Most linux distributions rename these, or rather, udev does, to a name unique to each physical interface. I do not like this, and EasyOS does not have this renaming (it is simply a matter of removing a certain rules file from the udev (or systemd) package). The method employed by Alex, is, I think, much more intelligent, and we get to keep the kernel-assigned names.

If you look above, you will see that next, /etc/net/mode-lan0 got called, with the kernel-assigned name (in this case "eth0") passed in. This is the content of 'mode-lan0':

#!/bin/sh
echo "+++ mode-lan0 $1"
ifconfig $1 up
ifctl $1 auto-dhcp

Then, after plugging in the ethernet cable, /etc/net/conf-request got called:

#!/bin/sh
echo "+++ conf-request $1"
dhcp $1 request

The 'dhcp' utility responds by obtaining a lease from the DHCP server on the router. Note, 'dhcp' is just a client. It is tightly integrated with the other utilities.

When the lease is obtained, 'ifmon' calls /etc/net/dhcp-dns, passing in the nameserver IP addresses, as you can see above. This is the content of 'dhcp-dns':

#!/bin/sh
echo "+++ dhcp-dns $@"
[ "$1" == "" ] && exit
echo "#written by /etc/net/dhcp-dns" > /etc/resolv.conf
for aIF in $@
do
 echo "nameserver ${aIF}" >> /etc/resolv.conf
done

...I had to do that, as apps such as the browser need that info in /etc/resolv.conf for Internet access.

When I unplugged the cable, 'conf-cancel' got called:

#!/bin/sh
echo "+++ conf-cancel $1"
dhcp $1 cancel

So, the only thing that we need to do is run 'ifmon' at bootup. Which I will be integrating into EasyOS.

EDIT: Alex has read this blog post, and responded here:
https://github.com/arsv/minibase/issues/5#issuecomment-461873169

I have not got onto wifi yet, and that is most exciting, as Alex has written the utilities from scratch. There is 'wsupp' which replaces 'wpa_supplicant'. The latter has been troublesome, and I am eagerly anticipating what is coming...

Tags: easy