Karl O. Pinc wrote:
>> Whether I'm accessing it physically or via ssh, can't I use something
>> like:
>> udevadm test /sys/class/net/$ETHX 2>/dev/null | grep NET
>> or
>> udevadm test-builtin net_id /sys/class/net/$ETHX 2>/dev/null
>> ...? That worked for me even on Jessie machine.
>
> I don't know. I just tried both the above on a
> jessie box running on a VM and it did not show me
> an ID_NET_NAME_PATH, which I presume is what
> shows me the new-style interface name?
(By "$ETHX" I mean "eth0 or whatever you've currently got"...)
Is the VM one that supports the ports-and-slots scheme? Some
apparently don't. I don't know exactly what happens instead, but
udevadm seems the most reliable way of narrowing that down.
> I don't have a stretch box with old-style names to test on.
If I boot a physical stretch box with the net.ifnames=0 option, it
comes up with an eth0 but udevadm says ID_NET_PATH=enp1s0.
I know udevadm worked for me on physical machines running jessie,
since that's how I predicted their names for my own upgrades. But if
it *is* the officially approved way of predicting predictable names, I
wish the upstream docs would say so.
Okay, here's a significantly trimmed-down version that we might be
able to use if it's bulked out with good external references.
In issues.dbk:
<section id="migrate-interface-names">
<title>Migrating from legacy network interface names</title>
<para>
If your system was upgraded from an earlier release, and still uses
the old-style network interface names that were deprecated with
stretch (such as <literal>eth0</literal> or <literal>wlan</literal>),
you should be aware that <systemitem role="package">udev</systemitem>
in buster no longer supports the mechanism of defining their names via
<filename>/etc/udev/rules.d/70-persistent-net.rules</filename>. To
avoid the danger of your machine losing networking after the upgrade
to buster, it is recommended that you migrate in advance to the new
naming scheme (usually meaning names like <literal>enp0s1</literal> or
<literal>wlp2s5</literal>, which incorporate PCI bus- and
slot-numbers). Take care to update any interface names hard-coded in
configuration for firewalls, <systemitem
role="package">ifupdown</systemitem>.
and so on.
</para>
<para>
The alternative is to switch to a supported mechanism for enforcing
the old naming scheme, such as the <literal>net.ifname=0</literal>
kernel commandline option or a systemd <filename>.link</filename>
file.
</para>
<para>
To find the new-style names that will be used, first find the
current names of the relevant interfaces:
</para>
<screen
$ echo /sys/class/net/[ew]*
</screen>
<para>
For each one, check whether it is used in configuration files:
</para>
<screen>
$ sudo rgrep -w eth0 /etc
</screen>
<para>
And what name <systemitem role="package">udev</systemitem> would prefer to
use for it:
</para>
<screen>
$ udevadm test-builtin net_id /sys/class/net/eth0 2>/dev/null
</screen>
<para>
(One of these may be a fallback MAC-based name, sometimes needed
for USB network hardware.)
</para>
[Possibly add extra details there for other special cases]
<para>
To switch over, disable <filename>70-persistent-net.rules</filename>
either by renaming it or by commenting out individual lines.
On virtual machines you will need to remove the files
<filename>/etc/systemd/network/99-default.link</filename> and
(if using virtio network devices)
<filename>/etc/systemd/network/50-virtio-kernel-names.link</filename>.
Then rebuild the <filename>initrd</filename>:
</para>
<screen>
$ sudo update-initramfs -u
</screen>
<para>
and reboot. Your system should now have new-style network interface
names. Adjust any remaining configuration files, and test your system.
</para>
[possibly a paragraph about safe upgrades over SSH]
<para>
See the
<ulink
url="https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/";>upstream
documentation</link> and the <literal>udev</literal>
<filename>README.Debian</file> for further information.
</para>
</section>
And/or maybe a pointer to some useful page in the Debian Wiki, but I
suspect we'd need to write one first.
Then in upgrading.dbk
<section id="review-interface-names">
<title>Verify network interface name support</title>
<para>
Systems upgraded from older releases that still use network interfaces
with names like <literal>eth</literal> or <literal>wlan</literal> are
at risk of losing networking once they switch to buster; see
<xref linkend="migrate-interface-names"/> for migration instructions.
</para>
</section>
--
JBR with qualifications in linguistics, experience as a Debian
sysadmin, and probably no clue about this particular package
