I notice /etc/hosts has a line with current IP address and hostname and possible domain just after localhost.
How do you keep it correct when getting its IP address from DHCP (since it changes)?
I'm using debian, by the way.

Did you change it and why?

Is myhost your machine name? check it with hostnamectl

Edit it, delete all and add:

127.0.0.1 localhost
127.0.1.1 myhost.lan myhost

If you using IPV6 settings on DHCP you also should have this:

::1 localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters


You don't need to change your ip there only to test dns for locally purposes, and it's not recommended.

In other words you will have another ip via dhcp working regardless of that file and you don't need to restart services.

The DHCP server (modem/router) should have a way to make that address permanent or a never ending lease.

Otherwise just set it static.

1 members found this post helpful.

Sorry it seems I misunderstood the question but anyway that's not the way to make it permanent like was said is via your router or /etc/network/interfaces configuration or your network manager graphically.

I don't necessarily have control over DHCP servers everywhere I connect my laptop to...

Yes, myhost is the hostname.
example.com is my domainname.

I still lag behind regarding IPv6 configurations! I'll have to look into that...

I thought of just deleting the line with the hostname (with the transient IP address) leaving just the one with "localhost", but I am aiming for correctness - I'd like to have tools like hostname and others report correct hostname, domainname, FQDN...

Next question will be the same but for /etc/networks. :-)

You want to use debian as server? Or just set static ip in every lan you connect? (this later not every networks support)

I was thinking more of laptops with DHCP.
They get carried around between several networks, some controlled by me, some not so. Some are friendly some are not...
I'd like to have the current (transient, correct) domain name appear on the login screen, tools like route report the correct networks...

Having the local domain name appear on the login screen would be (almost) a magic trick since the laptop would have no communication with that network (not even the AP) until powered on and would have nothing from dns on the network until already logged in and authenticated. The connection to the AP does not AFAIK do any DNS handshaking.

You need some sort of script to do that. I have never done it before, even with radius, when you login that is.
Otherwise you can add a conky file with that info or add it to conky.

FQDN you don't need it since you're not a server. But should be something like this:

hostnamectl set-hostname ninguem

You can edit hosts, and comment line 127.0.1.1 - it's debian related and no need for it.

127.0.0.1 ninguem.myhostname.org ninguem

hostaname
ninguem
hostname -f
ninguem.myhostname.org
dnsdomainname
myhostname.org

The debian wiki page about setting IP is very complete: https://wiki.debian.org/NetworkConfiguration

you can set the interfaces depending on what are you using as network manager in that wiki you have explanation

ip addr show

a simple static for interface wlp2s0 should be:

allow-hotplug wlp2s0
iface wlp2s0 inet static
#wpa-ssid xxxxx
#wpa-psk xxxxx
address 192.168.1.66
network 192.168.1.0
netmask 255.255.255.0
broadcast 192.168.1.255
gateway 192.168.1.1
dns-nameservers 208.67.222.222 208.67.220.220


trouble with ipv6
- systemd
echo "net.ipv6.conf.all.disable_ipv6 = 1" >> /etc/sysctl.conf
sysctl -p

-openrc
echo "net.ipv6.conf.all.disable_ipv6 = 1" >> /etc/openrc/sysctl.d/sysctl.conf

-runit
edit file /etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1"
GRUB_CMDLINE_LINUX="ipv6.disable=1"

and
update-grub

You might be right. The solution I think will have to be creating a script for post-dhcp. A script in /etc/dhcp/dhclient-exit-hooks.d/, I guess.
I'm not sure what you mean with conky. Those applets floating on the desktop? Nahhh! :-)
Why do you say this? Shouldn't all computers have its FQDN correctly set?
Hum!...
I don't have that line. But what is it for, really?
Thank you. I'll have a look into it. Again...

This quest aims for correctness, not a practical necessity I have right now. I'm being pedantic, I guess...
But picture this situation: You BYOD to a place to start working there (It could be a friend you want to help debugging network issues at home).
You connect to a network, but you want which network to be immediately apparent so you don't hack his neighbor network by mistake.
Makes sense?

I have always understood that you should NEVER remove the
part in the /etc/hosts file since a lot of what happens locally depends on that.

I have understood that additional hostnames can be inserted with those same IPs, but that those should not be removed.

Is that information no longer valid?

We where talking about 127.0.1.1 , not 127.0.0.1.
Notice the third number.
I certainly still have 127.0.0.1.