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Udev: Ugly? Bad? Good?… Or Bleeding Edge?

02/04/2013 @ 7:30 pm - 11:00 pm

Reminder:

This is on Tuesday 02/04/2013

 

Or: How not to do an update!

This talk is a little story for one example where a few bits went astray for my own experience of a slightly messy update to Gentoo… This is also a bit of an ‘expośe’ of how FLOSS works 🙂

Don’t worry about all the cryptic names. It’s the surrounding stories and bun-fight that’s fun! 😉

Udev…

linux-modular-tux_1k

… is changing and merging into/with something new and something controversial. All a very radical change to replace a critical part that has for too long many years remained almost unchanged since SysV Unix!…

Never heard of udev? Don’t worry… It’s one of those kernel-thingies that should never be seen. Which is all well and fine when it “Just Simply Works”… And full credit to Linus and many others for where the “Just Simply Works” usually works very well in the world of Linux.

The ‘working well’ has to include not ‘breaking’ other system details. One of Linus’ more famous rants is that of: “WE DO NOT BREAK USERSPACE! Seriously.” (That Slashdot discussion of the LKML thread goes off rambling somewhat. A more succinct summary is given on “YOU DO NOT BREAK USER SPACE!”.)

So… This is a little story of when udev unexpectedly became ‘visible’ for my one small example, dragging in the controversy surrounding systemd and OpenRC and “how ‘best’ to do things”. All ‘just’ for the sake of a something different init?…

 

All at:

Fellows Morton and Clayton
54 Canal Street
Nottingham, NG1 7EH
Telephone: 0115 9506795

latitude = 52.948615
longitude = -1.148431
Google map

Food is also served up until 8pm.

For the expected cold evening, we’ll be initially huddled near the bar to then later move over to a quiet area with promised hot air to warm our meeting. Just look for the Linux mags and gadgets (or ask the friendly bar staff where to find us 🙂 ).

 

Tuesday 02/04/2013:

  • 7:30pm: Meet
  • 8:00pm: Discussions/Talks

 

All welcome!

Cheers,
Martin

 

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Details

Date:
02/04/2013
Time:
7:30 pm - 11:00 pm
Event Category:

Venue

Fellows Morton and Clayton
54 Canal Street
Nottingham, NG1 7EH United Kingdom + Google Map
Phone:
0115 9506795

2 comments to Udev: Ugly? Bad? Good?… Or Bleeding Edge?

  • Martin L
    04/05/2013 at 1:27 am

    There is now a wiki-page to explain fixing up after the recent udev update:

    Udev/upgrade

    Be careful when upgrading udev, you will need to consider the changes listed below; ignoring them can break your system!…

    udev 200 …

    Note the code example to see what you’ll get for your network interfaces:

    udevadm test-builtin net_id /sys/class/net/eth0 2>/dev/null

  • Martin L
    26/06/2013 at 3:37 pm

    A timely reminder for the udev (re)naming of network interfaces: From the emerge messages for udev 204:

    * Messages for package sys-fs/udev-204:
    *
    * The new predictable network interface names are used by default, see:
    * https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames
    *
    * Example command to get the information for the new interface name before booting
    * (replace with, for example, eth0):
    * # udevadm test-builtin net_id /sys/class/net/     2> /dev/null
    *
    * You can use kernel commandline net.ifnames=0 to disable this feature.
    *
    * You need to restart udev as soon as possible to make the upgrade go
    * into effect. The method you use to do this depends on your init system.
    *
    * For more information on udev on Gentoo, upgrading, writing udev rules, and
    * fixing known issues visit:
    * https://wiki.gentoo.org/wiki/Udev/upgrade
    * https://www.gentoo.org/doc/en/udev-guide.xml

    OK… So the “udevadm test-builtin” can be used to find out what you should get after moving to the new udev. To find out what you actually have once updated/rebooted, you can use:

    cat /proc/net/dev

    One good check to see what needs changing for the udev ‘persistent’ interface names is to run for example:

    egrep -R 'eth[0-9]' /etc

    Note to update any net.xxxxxx symlinks in /etc/init.d/ as necessary if you start your interfaces there. Also, /etc/conf.d/net will need to be updated.

    A few links for further details:

    One pertinent comment by Lennart on Flameeyes’ Weblog is:

    … We specifically bind names to the “stable” bits of device paths, since we want to allow people to replace broken hw. As long as you plug things in at the same physical location the naming won’t change. If you plug in your hw into another location the name will change, however. If you prefer binding the naming to actual specific devices you bought, you can choose to name things after the MAC address, but that’s just an option. In general we chose to default to fixed-by-path rather than fixed-by-identity since we had to pick some default and it appeared to be smarter to allow replacing bad hw than anything else. …

    Hopefully of help!

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