dnf-plugin-ovl

Workaround to run dnf on overlayfs. A port of yum-plugin-ovl to dnf.

When you need it

Running dnf (or yum or rpm) with the RPM database on an overlayfs mount (e.g. in a container) will result in errors similar to

rpmdb: BDB0060 PANIC: fatal region error detected; run recovery

or

error: rpmdbNextIterator: skipping h# 173 blob size(4836): BAD, 8 + 16 * il(70) + dl(3708)

as soon as you run dnf on different layers when building an image.

Install

It is included in Fedora's repository and EPEL:

dnf install -y dnf-plugin-ovl

Verifying installation

dnf updateinfo -v

Should show (second line only if an overlayfs system detected):

Loaded plugins: ..., ovl, ...
OverlayFS detected

Background

Opening a file on an OverlayFS in read-only mode causes the file from lower layer to be opened, then later on, if the same file is re-opened in write mode, a copy-up into the upper layer takes place, resulting into a new file being opened.

Since dnf opens the RPMdb first read-only, and then also with write access, we need to copy-up the files beforehand to make sure that the access is consistent.

Building

rpmbuild --nobuild --nodeps dnf-plugin-ovl.spec  # Will fail, but creates missing dirs on new machine
spectool -g -R dnf-plugin-ovl.spec
rpmbuild --clean -v -bb dnf-plugin-ovl.spec