IP address and routes are gone after a reboot

Likely causes

1. The address and routes were set with ip commands only, never written to a file.
2. They were written, but to a file this system does not read (ifupdown, netplan and NetworkManager each have their own), or with a mistake in it.

Diagnose

Run these in order. The output is what each printed on a lab's real Linux machines.

laptop:~# ip addr show eth0

After the restart the card is DOWN with no inet line: no address.

11: eth0@if60211: <BROADCAST,MULTICAST> mtu 1500 qdisc noqueue state DOWN group default 
    link/ether 6e:a3:88:cd:55:09 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    altname homeNetwork

laptop:~# ip route

And the routing table is empty.

Fix

/etc/network/interfaces on laptop

On a Debian-style system (ifupdown), the card's address, mask, gateway and DNS server go in /etc/network/interfaces.

auto eth0
iface eth0 inet static
    address 10.0.1.10
    netmask 255.255.255.0
    gateway 10.0.1.2
    dns-nameservers 10.0.1.2

laptop:~# ip route

After the next restart, the routes come back by themselves.

default via 10.0.1.2 dev eth0 
10.0.1.0/24 dev eth0 proto kernel scope link src 10.0.1.10 

laptop:~# curl -sS -m 5 http://webServer.lab/

And the page loads by name.

hello from webServer

Break it and fix it yourself

Each lab is a small network of real Linux machines in your browser, where this fault happens.

• A bare machine: networking by hand Free: its challenge "Written down, still lost at boot" set the fault for you to find and fix.

Open A bare machine: networking by hand