Fix my Gentoo

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This guide has been elaborated in response to repeated posts to the forum by users that "nothing works". This article covers rescuing an installation when a chroot is not possible, when almost nothing seems to work but there is a need for certain binary packages to fix the system.

The case where gcc is broken after a --depclean isn't covered here. gcc-config is probably what is needed - be more careful using the --depclean option in the future.

It is actually very difficult to break Gentoo so badly that it can't be fixed.

Prerequsites

Some binary packages may be necessary to fix the system.

Binary packages may be found on a binhost or tinderbox on the web but they are unlikely to be built for the local system, with corresponding USE flags and CFLAGS.

This guide provides instructions on building binary packages that will work to use to fix a system. Neither another system, a spare partition or even another install will be required. All that is needed is:

  • A working internet connection.
  • A way to boot the broken box with some recovery media, e.g. SystemRescue, if it won't boot
  • About 20 GiB of free space on in the broken installation. 5 GiB may do, depending on what needs to be built.

Summary

As the bootable install is not working and a working install is needed to build binary packages, another install is needed (just an extracted stage3 somewhere). This install doesn't need to be bootable.

It is sufficient to be able to chroot into it and run emerge. This rescue install will share some elements with the broken install which saves space and makes things easier in the final steps.

Getting started

Terminology

  • /mnt/gentoo: Mount the broken installation here.
  • /mnt/gentoo/home/rescue: The new rescue install, it can be anywhere but it needs to be on a hard disk.

The rescue install

  • Mount the broken install at /mnt/gentoo to be able to use its hard drive space and its /var/db/repos/gentoo.
  • Make a directory at /mnt/gentoo/home/rescue or somewhere with free space:
    root #mkdir /mnt/gentoo/home/rescue
  • Follow the handbook to fetch a stage3 tarball and untar it to /mnt/gentoo/home/rescue.
  • Do not get a Portage snapshot, the one in the main install will be utilized.
  • Follow the Handbook for all the odds and ends, like copying /etc/resolv.conf.

Mounts

  • Mount /dev and friends in /mnt/gentoo/home/rescue just as if doing a new install but do not chroot yet.
  • Bind mount the main ebuild repository to the rescue system:
    root #mount -o bind /mnt/gentoo/var/db/repos/gentoo /mnt/gentoo/home/rescue/var/db/repos/gentoo
  • Bind mount the distfiles directory:
    root #mount -o bind /mnt/gentoo/var/cache/distfiles /mnt/gentoo/home/rescue/var/cache/distfiles
  • Bind mount the binary package directory:
    root #mount -o bind /mnt/gentoo/var/cache/binpkgs /mnt/gentoo/home/rescue/var/cache/binpkgs
  • Copy over /mnt/gentoo/etc/portage to /mnt/home/rescue/etc/portage:
    root #cp -r /mnt/gentoo/etc/portage /mnt/gentoo/home/rescue/etc/portage

Now the rescue install has all the settings from the broken installation.

Chroot in to rescue install

Follow the chroot instructions from the handbook but into the /mnt/gentoo/home/rescue directory instead.

Edit /etc/portage/make.conf

Inside of the new working rescue chroot, Portage must be told to create and save binary packages of everything we build.

Edit /etc/portage/make.conf by adding buildpkg to FEATURES.

This causes Portage to save binary tarballs of every package built to /var/cache/binpkgs.

Warning
Do not emerge --sync. Packages that match the state of the broken installation are needed; this requires the repository to be in the same state.

Building packages

Two choices:

  1. quickpkg
  2. emerge

Quick package (quickpkg)

Warning
Take care with quickpkg, it either drops configuration files or copies them in their current state from the install. This may be undesirable.

If the package needed is part of the stage3, use the quickpkg tool to make a binary package.

Emerge

emerge will just work within the stage3 extracted. Build something small as a test like sys-apps/sed then check that the package has appeared in /var/cache/binpkgs.

More packages

emerge whatever is needed. /home/rescue will stay around until deleted and it is only a chroot away. Upon return, don't forget to redo the bind mounts.

Installing binary packages

After creating binary packages using any of the methods described above, they must be installed somehow to the broken system.

The best method to install binary packages depends on what is broken. The options below are presented in increasing order of risk (least risky first):

  1. Install "properly" using emerge where it works.
  2. Use qmerge (which doesn't need Python, it's part of app-portage/portage-utils.
  3. Raw extract with tar the binpkgs (tarballs) onto the broken system until the safer option can be used.

Using emerge

This requires chrooting into the install to be rescued. If a part of the toolchain is missing, this should work. Run:

root #emerge -K <package/atom>

This will either install the binary tarball and its dependencies or fail if the binaries cannot be found.

Using qmerge

Outside of the chroot, run:

root #qmerge <package/atom>

Using tar

If a chroot canot be created, emerge is not an option. Maybe sys-libs/glibc is missing and there is no statically linked sys-apps/busybox?

Each binary package is like a single package stage3. It has some extra information on the end that Portage uses, which will provoke a warning from tar that can be safely ignored.

Warning
There is no safety net, tar will just spray files all over the filesystem.

Extracting tar step-by-step method

For safety's sake, unmount the rescue install at /mnt/gentoo/home/rescue.

root #umount /mnt/gentoo/home/rescue

It may be necessary to unmount all the things mounted inside /mnt/gentoo/home/rescue first.

Sanity checks

Before issuing the tar command, verify:

  • The install is mounted at /mnt/gentoo
  • Understand the -xpf and -C options to tar. Review the man page if unsure:
    root #man tar
Understanding the tar command
Warning
The -p option is essential. Without it, tar will work, the files will be installed but execute permissions will be dropped.
Warning
Check the destination path: -C /mnt/gentoo, this is where all the output files will be sent.
Tip
tar will work out the compression for itself, so the -j option is not required.
root #tar --xattrs -xpf /mnt/gentoo/var/cache/binpkgs/<package/atom> -C /mnt/gentoo

This tells tar to extract, preserving permissions, the file /mnt/gentoo/var/cache/binpkgs/<package/atom> and Change directory to /mnt/gentoo before it does anything else.

In fact, the input file name above is not correct. The full path to the tarball is required. Tab completion helps a lot.

Nervous users can add the -v option to tar.

Extract

As described above, unpack the tarball (binary package) into the broken system.

root #tar --xattrs -xpf /mnt/gentoo/var/cache/binpkgs/<package/atom> -C /mnt/gentoo

The package is now effectively installed to the broken install. Repeat as necessary for all packages until emerge can be used (see above) instead.

Tidying up

Once the damage is fixed, delete /home/rescue, or keep it around for next time.

With adequate space, it may be desirable to add buildpkg to the FEATURES variable as a regular thing. Then, the tarballs needed for rescuing the system will already exist.

Both /var/cache/distfiles and /var/cache/binpkgs will grow without limit. Run eclean occasionally to prune them.

See also