Gentoo FTW!

posted 4 years ago by Ben Cordero

These past few weeks, there have been some pretty disturbing disruptions for Linux users on rolling release distros.The biggest upset in recent times I'll describe as "The udev-200 issue", where the symptoms of an unsupervised update/reboot cycle will present you with a) a system that won't boot, b) a system without network or c) both.

Disruptions of this kind are not pleasant for end users. In the time that I've been using Linux, I have seen the effect of quite a number of transitions: KDE 3/4, Gnome 2/3, X11 automatic configuration, libpng2, Linux 2.6/3. Thankfully, future generations need not worry about these things since all distributions have made these jumps and the remnants are bitrotting in Google's index.

We are still going through some, python2/3 (and packaging in general), sysvinit/systemd, X11/Wayland, Grub2/UEFI, IPv4/v6. These won't be solved overnight. The problems should resolve themselves over a time span of years, but I suspect that they will be solved.

Gentoo has just come through some particularly nasty ones in the past few months: udev-200 is the most recent, but EAPI=5 with an out-of-date portage back in February, I now have a habit of trialling upgrades on VMs these days which are easy to do with the prolific tooling available.

In the more usual distros, time release or feature release based worlds can not handle the adaptability. I have never had an upgrade of Ubuntu work flawlessly, something always breaks, I don't even know how to approach the problem in Fedora/RedHat land. Debian has a whole chapter devoted to this.

Typically, when an upgrade of magnitude is about to occur, it is time for the annual "dd if=/dev/zero of=/dev/sda" and reinstall. Biannual if you use Windows.

In Gentoo, this is unacceptable. Changes to a rolling release cycles must be gradual. A transition plan in place and users notified and prepared beforehand about what the technical issues are. It is good that in most cases, upstream developers and distro developers find a way to make the upgrade process seemless.

(I think it is still good to know what could have broken, and especially how to fix it if it did. None of this re-install from scratch/golden image+backups absurdity.)

Gentoo has the tools to handle these advances properly. Often, I am asked why I still use it when "Arch is obviously better" (configurability with none of the compiling) or "Just use Ubuntu, everyone else is!". I cry a little inside. So I've put together a short list of features that need to be available before I could ever consider distro-hopping again.

Modular Networking using key=value pairs

I've tried debian-esque /etc/network/interfaces. It's terribly inconsistent and requires constant referencing to do anything but basic dhcpv4.

Here's my current conf.d/net.

modules="dhclient iproute2"
bridge_add_eth0="br0"  
bridge_add_eth1="br0"  
bridge_add_enp3s0="br0"  
bridge_add_enp1s6="br0"
config_eth0="null"  
config_eth1="null"  
config_enp3s0="null"  
config_enp1s6="null"
config_br0="192.168.1.2/24  
2001:xxxx:xxxx:xxxx::2/64"  
routes_br0="default via 192.168.1.1  
default via 2001:xxxx:xxxx:xxxx::1"  
dns_domain="my.domain"  
dns_search="192.168.1.1 2001:xxxx:xxxx:xxxx::1"

This is will be my network configuration for a little while until udev-200 issues blow over and I have a bit more confidence. In particular:

Attaching VMs to the network is easily achieved by adding them to the bridge. I have personal experience that both Xen4 and LXC handle this nicely. Qemu/KVM need a separate if-up/down.sh script which can get tricky, but nonetheless works.

I have more complicated setups too, my gateway/firewall has a few extra stanzas to handle ppp. At work I have deployed Gentoo on Cisco UCS which pulls VLANs out of two Bonded/Etherchannel 10 Gig fiber cards.

revdep-rebuild

DLL-hell was a big problem. Upgrading a library would cause untold havoc on applications that depended on installed-at-build-time dependencies. In modern Windows, programs are completely housed under their C:\Program Files\ namespace. OS X Frameworks takes this even further. And Ubuntu still breaks on dist-upgrade.

The effect isn't as noticeable these days, but the install/uninstall/upgrade breakages got annoying. Gentoo's solution was to recompile broken packages against the newly installed libraries. FEATURES=preserved-libs mitigates the issue in an efficient way. Portage will keep the old library around (without name clashing) until the reverse dependencies have been upgraded or recompiled against the newer version of the library. When no more packages depend on the old files, they are removed.

CONFIG_PROTECT and dispatch-conf

Another problem with upgrades is that configuration files and init-scripts evolve. New options are added, defaults are changed, hacks are removed. The etc-update mechanism is a neat wrapper to diff and $EDITOR for sysadmn intervention. OpenSUSE just gained this ability.

epatch-user, egit-src

Compiling from source. More specifically, modifying the source before it is installed. This could be modifying some source code for a failed build, then resuming. Adding a custom patch during the build process via epatch-user hooks, or just living on the edge with code fresh from the repo.

More commonly, I use this feature to repair broken emerge runs, or fixing some build options before a package is fully merged into the real filesystem.

# Example taken from my personal overlay  
ebuild /usr/local/portage/net-misc/balance-fm/balance-fm-1.0.1-r1.ebuild compile
# Hack hack hack  
cd /var/tmp/portage/net-misc/balance-fm-1.0.1-r1/work/balance-fm-1.0.1/  
$EDITOR Makefile  
# Don't forget to make patches to record changes, and save them somewhere safe.
# recompile  
rm /var/tmp/portage/net-misc/balance-fm-1.0.1-r1/.compiled  
ebuild /usr/local/portage/net-misc/balance-fm/balance-fm-1.0.1-r1.ebuild compile
# install the changed package  
ebuild /usr/local/portage/net-misc/balance-fm/balance-fm-1.0.1-r1.ebuild merge

This is a good technique during ebuild development that keeps everything installed tracked by portage and uninstallable.

Philosophically, I find this morally pleasing because there is a direct correlation between what is installed on my filesystem and the GNU definition of corresponding source.

I might come back to this topic later because this blog post is getting long and you have probably ctrl+w'ed by now.

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