I really wanted to look into the new kernel building solutions for Gentoo and maybe migrate to dracut, but last time I tried, ~1.5 years ago, the initreamfs was now working for me.

And now in 2023 I’m still running genkernel for my personal boxes as well as other servers running Gentoo.

I guess some short term solutions really become defined tools :P

So this is how I rebuild my kernel nowadays:

1. Copy old config

   1 2	cd /usr/src cp linux-6.1.38-gentoo/.config linux-6.1.41-gentoo/

2. Remove old kernel build directories

   1	rm -r linux-6.1.31-gentoo

3. Run initial preparation

   1	( eselect kernel set 1 && cd /usr/src/linux && make olddefconfig )

4. Call genkernel

   1 2 3 4 5 6 7 8 9 10 11 12

   genkernel \ --no-menuconfig \ --no-clean \ --no-clear-cachedir \ --no-cleanup \ --no-mrproper \ --lvm \ --luks \ --mdadm \ --nfs \ --kernel-localversion="-$(hostname)-$(date '+%Y.%m.%d')" \ all

5. Rebuild the modules

   If in your /etc/genkernel.conf you have MODULEREBUILD turned off, then also call emerge:

   1	emerge -1 @module-rebuild

Intro

Backing up using this method takes a lot less space - ~60MB (without distfiles) and can be restored on almost any system (running portage) and tweaked afterwards for, say, CPU architecture. I've created a a short script with similar method in here.

What we need

• ebuild repositories are installed with git
• distfiles (those might be gone when we want to replicate)

Backup

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24

# System info
emerge --info > info.txt

# Portage tree
cp -Lr /etc/portage .

# Portage layout
tree -a -L 2 /etc/portage > layout.txt

# Packages in @world
cp /var/lib/portage/world .

# Installed sets
cp /var/lib/portage/world_sets .

# Installed packages (with versions)
qlist --installed --nocolor --umap > qlist-use.txt
qlist --installed --nocolor --verbose > qlist-ver.txt

# Distfiles
cp -rv "$(portageq envvar DISTDIR)" distfiles

# Ebuild database
cp -r /var/db/pkg pkgdb

Restoration

To faithfully restore the system perform those actions as root

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17

# Copy the portage tree to /etc
rm -dr /etc/portage
cp -r portage /etc/portage

# Checkout the gentoo repo to a commit specified in info.txt
cd "$(portageq get_repo_path / gentoo)"
git checkout # <commit ID>

# Copy distfiles
cp -r distfiles/* "$(portageq envvar DISTDIR)"/

# Fake-install @world and sets
cp world /var/lib/portage/world
cp world_sets /var/lib/portage/world_sets

# Emerge the exact packages from qlist-ver.txt
emerge --keep-going=y -1Oav $(sed 's/^/=/' qlist-ver.txt)