Re: hostname is being reset, killing net on reboot
On Fri, Jan 21, 2022 at 09:34:35PM -0500, gene heskett wrote:
> /etc/resolv.conf has:
> search coyote.den
> nameserver 192.168.xx.1
>
> the search line says to look in the /etc/hosts file, failing that, the
> nameserver line sends the dns lookup query to the router
No, that's not correct.
The config file that says "look in /etc/hosts first, then look in DNS
next" is /etc/nsswitch.conf. Specifically, it's the line that begins
with "hosts:" in that file.
The "search" line in /etc/resolv.conf means "if I type ftp roadrunner,
I want it to act as if I had typed ftp roadrunner.coyote.den".
In other words, it's the default DNS search domain for looking up the
*other computers* on your local area network.
> However when I set hostname with hostname, the 169.bs stays out of the
> picture and networking works the world until a reboot.
Well, yes. The "hostname" command sets the current hostname, which resides
in memory only. It has no permanent effect.
And it has nothing at all to do with IP addresses. Or DNS.
> Setting the hostname with hostnamectl to the alias in /etc/hosts for this
> machine, gets me exactly the same hostname but then the route reported by
> "ip a" is the 169.bs.bs.bs and I can't get out of my shirt pocket to even
> ping the router at 192.168.xx.1.
Routing has nothing to do with your system's hostname. At all.
At the most basic level, your system's default route is set by whatever
mechanism sets up your network interfaces. On Debian, this can be any
of *several* different pieces of software, depending on what's installed
and what you've got in your config files.
In the *most* basic possible configuration, your routing table will be
one automatic entry for your ethernet interface (created from the IP
address and netmask which are assigned to that interface), and then one
"default" route which is assigned for reaching every host that's *not*
part of your LAN.
E.g. in /etc/network/interfaces you'd have something like this:
auto enp2s0
iface enp2s0 inet static
address 192.168.1.21/24
gateway 192.168.1.1
This tells the "ifupdown" software package that you'd like it to manage
the enp2s0 network interface, assigning the IP address 192.168.1.21 with
a 24-bit netmask, which automatically creates a route to the 192.168.1.0/24
network. In addition, it will create a default route via the 192.168.1.1
address.
None of this has *anything* to do with your system's hostname.
None of this has *anything* to do with your /etc/hosts file.
None of this has *anything* to do with DNS.
Of course, there are many other ways to configure network interfaces in
Debian. You might be using Network-Manager, for example. Or systemd's
systemd-networkd(8). Or you might be using /etc/network/interfaces but
telling it to ask for configuration from DHCP.
Also, by the way, "ip a" does not report routes. That's "ip r".
unicorn:~$ ip r
default via 10.0.0.1 dev lan0
10.0.0.0/24 dev lan0 proto kernel scope link src 10.0.0.7
------------------------------------
You're probably still confused. Let's go over everything again, from
the beginning.
Your computer has a *network interface*. This interface has some kind of
name. The names are very complicated and I don't want to introduce that
particular piece of complexity here. Let's say that you've somehow
managed to determine your interface's name. Let's say, for this example,
that your interface's name is enp2s0.
In order for your network interface to *work*, it has to be assigned an
IP address and a netmask. This can come from DHCP, or it can come from
files that you configure on your system.
With an IP address and a netmask, you will be able to communicate with
other computers on your *local area network*, by using their IP addresses.
If you have a default route, then you can potentially talk to computers
*outside* of your LAN. This default route can come from DHCP, or from
local files. E.g. with a properly configured default route, you will be
able to run commands like "ping 8.8.8.8" and get responses.
If you'd like to communicate with other computers by name instead of by
IP addresses, you can either put their names and IP addresses in the
/etc/hosts file (a simple text file), *or* you can configure your
computer to use DNS.
DNS is configured in the /etc/resolv.conf file. The most basic piece
consists of "nameserver" lines which contain the IP addresses of DNS
resolvers which will look up computer names for you. These nameservers
can come from DHCP, or they can be configured in your local files.
Your computer can also have a hostname. This is how your computer
identifies itself when it logs things, so that you can tell which computer
wrote which piece of the logfile. Your computer can be named whatever
you like. Its name has meaning only to you. Other computers do not
know what your hostname is, and they do not care.
If you want other computers to be able to contact you by a name, then
you add that name to DNS, *or* to the /etc/hosts files of those other
computers. The name that you put in DNS or other machines' /etc/hosts
files does *not* have to be the same as your hostname. Your hostname
is private. It's what your computer calls itself. It's not what
other computers call you.
Your computer can also have a *list of search domains* for use in
hostname lookups. This is typically something you'd only care about
if you have a LAN with multiple computers on it, which all want to
talk to each other. If you're just a single computer that's on the
Internet, you *do not care* about this at all.
The main purpose of a list of search domains is to save typing. Let's
say you've got a LAN with hosts that are (publically) called
"cat.coyote.den" and "dog.coyote.den". If you want to log into the
first one, you could type "ssh cat.coyote.den". But that's a lot of
typing. If you have "coyote.den" in your list of search domains, then
you can simply type "ssh cat". The host resolver will try each of the
domains in your search list, one by one, as suffixes, until one of
them works.
This list of search domains is configured in your local /etc/resolv.conf
file. It can be a static entry, or it can come from DHCP.
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