Nix and Guix for Gentoo

Gentoo overlay for Nix and GNU Guix functional package managers.

Enabling the overlay

Use standard repos.conf configuration for the overlay:

# make sure 'repos.conf' is present:
mkdir -p /etc/portage/repos.conf

# Add an entry
cat > /etc/portage/repos.conf/nix-guix.conf <<EOF
[nix-guix]
location = /var/db/repos/nix-guix
sync-type = git
sync-uri = https://github.com/trofi/nix-guix-gentoo.git
EOF

# Sync the overlay
emerge --sync

Finally, we need to unmask the overlay (this does not apply if your system is already running ~arch):

# create keywords directory:
mkdir -p /etc/portage/package.accept_keywords

# Unmask ~testing versions for your arch:
echo "*/*::nix-guix" >> /etc/portage/package.accept_keywords/nix-guix

# (guix only) Unmask hard-masked guile and guix:
mkdir -p /etc/portage/package.unmask
echo "sys-apps/guix::nix-guix" >> /etc/portage/package.unmask/nix-guix
echo "dev-scheme/guile"        >> /etc/portage/package.unmask/nix-guix
echo "dev-scheme/guile"        >> /etc/portage/package.accept_keywords/nix-guix

Setup

Nix

Installation

The installation follows typical process of installing a daemon in gentoo:

emerge nix
# on systemd systems:
systemctl enable nix-daemon && systemctl start nix-daemon
# on openrc systems:
rc-update add nix-daemon && /etc/init.d/nix-daemon start

Then relogin as your user to import profile variables and pull in package definitions:

nix-channel --add https://nixos.org/channels/nixpkgs-unstable
nix-channel --update

You are done!

Now it's a good idea to check basic functionality:

# run a program without installation:
nix-shell -p re2c --run "re2c --version"
> re2c 3.0

# install and run a program:
nix-env -iA nixpkgs.re2c --no-sandbox
> installing 're2c-3.0'

re2c --version
> re2c 3.0

nix-env -e re2c
> uninstalling 're2c-3.0'

Next steps to try nix in action:

• https://trofi.github.io/posts/196-nix-on-gentoo-howto.html
• https://nixos.org/manual/nixpkgs/stable/

Guix

Installation

The installation follows typical process of installing a daemon in gentoo:

emerge guix
# on systemd systems:
systemctl enable guix-daemon && systemctl start guix-daemon
# on openrc systems:
rc-update add guix-daemon && /etc/init.d/guix-daemon start

You will likely want to enable binary cache:

guix archive --authorize < /usr/share/guix/ci.guix.gnu.org.pub

First run

Upon first package installation Guix will create ~/.guix-profile symlink to /var/guix/profiles/per-user/${USER} (where ${USER} is your user account name in current shell).

In order to allow Guix to set all variables correctly execute those commands:

export GUIX_PROFILE="${HOME}/.guix-profile"
export GUIX_LOCPATH="${GUIX_PROFILE}/lib/locale"
source "${GUIX_PROFILE}/etc/profile"

The best way is to add the commands to your ${SHELL} profile file: ~/.profile / ~/.bash_profile / ~/.zprofile or equivalent.

To install a GNU hello package to test out Guix execute:

guix package -i hello

If you plan to use guix pull (and you probably are) you'll need to add it's PATH to your shell as well by following guix pull's suggestion:

export PATH="$HOME/.config/guix/current/bin:$PATH"
export INFOPATH="$HOME/.config/guix/current/share/info:$INFOPATH"

Next steps to try guix in action:

• http://trofi.github.io/posts/197-guix-on-gentoo-howto.html
• https://guix.gnu.org/manual/

Known problems and workarounds

Ideally the above setup should Just Work. In practice sometimes bugs happen outside nix or guix environments. When they come up and are not yet fixed upstream we will list them here with possible workarounds.

Missing sandbox support

The typical symptom is a failure to set the sandbox up when the build is required. Example test at rebuilding the package:

# fetching from cache:
$ nix-build --no-link '<nixpkgs>' -A hello
...
/nix/store/s66mzxpvicwk07gjbjfw9izjfa797vsw-hello-2.12.1

$ nix-build --check --no-link '<nixpkgs>' -A hello
error: this system does not support the kernel namespaces that are required for sandboxing; use '--no-sandbox' to disable sandboxing

Here error: this system does not support the kernel namespaces that are required for sandboxing is a symptom that your system fails to enable chroot sandbox that relies on kernel's PID and USER (mount) namespaces.

There are a few possible reasons for it:

1. Missing namespace support in the kernel

   Make sure you have those enabled:

   # zcat /proc/config.gz | grep -P 'CONFIG_USER_NS|PID_NS'
   CONFIG_USER_NS=y
   CONFIG_PID_NS=y
   

   Fix: build kernel with USER_NS and PID_NS support.

2. Already present read-only mounts within /proc

   These read-only entries are usually placed by by container managers like docker and systemd-nspawn. Example entries:

   # mount | grep proc
   proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
   proc on /proc/sys type proc (ro,nosuid,nodev,noexec,relatime)
   proc on /proc/acpi type proc (ro,nosuid,nodev,noexec,relatime)
   proc on /proc/asound type proc (ro,nosuid,nodev,noexec,relatime)
   proc on /proc/bus type proc (ro,nosuid,nodev,noexec,relatime)
   proc on /proc/fs type proc (ro,nosuid,nodev,noexec,relatime)
   proc on /proc/irq type proc (ro,nosuid,nodev,noexec,relatime)
   proc on /proc/scsi type proc (ro,nosuid,nodev,noexec,relatime)
   tmpfs on /proc/sys/kernel/random/boot_id type tmpfs (ro,nosuid,nodev,noexec,size=26371500k,nr_inodes=819200,mode=755)
   tmpfs on /proc/sys/kernel/random/boot_id type tmpfs (rw,nosuid,nodev,size=26371500k,nr_inodes=819200,mode=755)
   tmpfs on /proc/kmsg type tmpfs (rw,nosuid,nodev,size=26371500k,nr_inodes=819200,mode=755)
   

   Multiple ro mounts under /proc are a problem here. You need to find which mounts are causing the problem here. Some of them are safe and some are interfering with nix-daemon's /proc remount:

   See this post for more details on why it fails.

   Fix: TODO. Not sure what the correct fix here is yet. As a workaround to make sure it's the /proc masking issue you can unmount all of the /proc sub-mounts in the container:

   # umount /proc/kmsg /proc/scsi /proc/irq ...
   

   and restart nix-daemon.

   Maybe systemd's ProtectKernelTunables=no could help as a workaround?

   Healthy state should look like this:

   # mount | fgrep proc
   proc on /proc type proc (rw,nosuid,nodev,noexec,relatime)
   
   $ nix-build --check --no-link '<nixpkgs>' -A hello
   ...
   checking outputs of '/nix/store/ib3sh3pcz10wsmavxvkdbayhqivbghlq-hello-2.12.1.drv'...
   unpacking sources
   ...
   stripping (with command strip and flags -S -p) in  /nix/store/...-hello-2.12.1/bin
   /nix/store/...-hello-2.12.1
   

If you absolutely must disable sandbox then you can set sandbox-fallback = false in /etc/nix/nix.conf and restart nix-daemon. But things will leak out and break. You have been warned.

Environment variables breaking emerge

The symptom

/usr/sbin/gtk-encode-symbolic-svg: symbol lookup error: /guix/...-glibc-2.33/lib/libpthread.so.0:
  undefined symbol: __libc_pthread_init, version GLIBC_PRIVATE

This usually means your current environment contains unhandled variables. You can look at env output to find which ones mention /nix/* or /gnu/* store paths. Those are primary suspects.

Known problematic variables:

• none so far

Past examples:

• debugging poisoning by GDK_PIXBUF_MODULE_FILE (fixed)

The workaround

Once you figured out what variable causes problems you can add it to the list of ENV_UNSET variables in /etc/portage/make.conf. For example if it was a FOO_VARIABLE:

# /etc/portage/make.conf
#  can be removed once fix lands in ::gentoo:
#     https://bugs.gentoo.org/...
ENV_UNSET="${ENV_UNSET} FOO_VARIABLE"

Longer term fix

Longer term those variables should be reported in ::gentoo. See Past examples below for possible reports and fixes.

Pending fixes:

• none so far.

Past examples:

• GDK_PIXBUF_MODULE_FILE

Detailed description

Some nixpkgs and guix packages set various environment variables to redirect library loading from a default location to version-specific directory. Usually it is done via scripts wrapping binaries. For example firefox is a shell script that sets LD_LIBRARY_PATH, XDG_DATA_DIRS, GIO_EXTRA_MODULES, PATH and then calls .firefox-wrapped ELF executable.

Wrappers like that are usually contained to the wrapped program and don't normally cause problems to other packages. Unless such packages are able to spawn shells on their own. For example konsole exports QT_PLUGIN_PATH in it's wrapper. Another typical example is PATH variable.

The problem is not specific to nixpkgs or guix. Those are just most extensive environment variable users with many parallel incompatible environments available.

Normally emerge filters out problematic user variables by using profiles' defaults specified in ENV_UNSET in ::gentoo repository. For example it's current value is:

gentoo.git $ git grep ENV_UNSET | tr ' ' $'\n'

profiles/base/make.defaults:ENV_UNSET="DBUS_SESSION_BUS_ADDRESS
DISPLAY
CARGO_HOME
GDK_PIXBUF_MODULE_FILE
XAUTHORITY
XDG_CACHE_HOME
XDG_CONFIG_HOME
XDG_DATA_HOME
XDG_STATE_HOME
XDG_RUNTIME_DIR
PERL_MM_OPT
PERL5LIB
PERL5OPT
PERL_MB_OPT
PERL_CORE
PERLPREFIX
GOBIN
GOPATH"

Some (many!) variables are not yet filtered by it. They are either handled by portage explicitly (like PATH variables) or not handled at all.

Why use this overlay? Why not use official installation instructions?

That's a great question!

Here are installation instructions for:

• nix
  • one liner
  • step by step
• guix
  • one liner and step by step

Why not just run those?

The aspirational goal of this overlay is to make both nix and guix closer to typical packages one normally installs with emerge: installation, upgrade and uninstall should not require extra actions or special cleanups.

I'll list of some individual aspects below with their pros and cons to give the reader to decide on their own:

Install, Upgrade and Uninstall

Ebuild pros:

• install, upgrade and uninstall are done just like any other package via emerge (and via service registration). No need to update nix-daemon via nix package mechanism. Daemon just works.
• no need to manage separate root-based nix package just to update nix-daemon. Managing user's configurations is enough.
• rollbacks are done by emerging previous package version
• the binaries are built from source package using user's USE, CFLAGS and libraries. That makes nix and guix more adaptable to the environments where official binaries don't work as is.
• needed users and groups are installed and uninstalled along with the package. Adding extra groups to builders (like kvm) can be done via make.conf overrides with all power of man acct-user.eclass.
• the nix and guix binaries are installed to their usual /usr locations (nixpkgs packages still use nix as expected).
• all created files and directories are tracked by package manager, allow for natural cleanup on uninstall (apart from /nix/).
• ebuild does a bit of environment validation to make sure host kernel supports enough features to run nix build containers.

Ebuild cons:

• ebuild retraces the steps of the official install script: it very occasionally gets them wrong (usually on major updates). That might cause overlay-specific bugs.
• the binaries are built from source package using user's USE, CFLAGS and libraries (same as cons): feature set (and bug set) might be different from official upstream binary.
• by default nix-daemon version is defined by the ebuild, not by the package version installed via nix. It should not be an issue, but it's a deviation from typical setup.