Changes/RelocateRPMToUsr

Relocate RPM database to /usr

Summary

Currently, the RPM databases is located in /var. Let's move it to /usr. The move is already under way in rpm-ostree-based installations, and in (open)SUSE.

Owner

• Name: Chris Murphy, Michel Alexandre Salim, Neal Gompa
• Email: bugzilla@colorremedies.com, michel@michel-slm.name, ngompa13@gmail.com

Current status

• Targeted release: Fedora Linux 36
• Last updated: 2022-01-18
• devel thread
• FESCo issue: #2731
• Tracker bug: #2042099
• Release notes tracker: #791

Detailed Description

Current location

/var/lib/rpm

New location

/usr/lib/sysimage/rpm

/var/lib/rpm will be a symlink pointing to /usr/lib/sysimage/rpm

• The RPM database primarily describes the state of /usr. Storing the databases in /usr will more easily facilitate OS snapshots and rollback, without affecting /var.
• The need for moving rpmdb to /usr was brought up in a 2017 thread on the upstream rpm-maint@ list. Various locations for rpmdb (and similar databases) is discussed in the thread, with the end result being /usr/lib/sysimage/rpm.
• There's upstream RPM, rpm-ostree, and (open)SUSE agreement for this location.

Note: Changing the file system layout to accommodate a snapshot+rollback regime is implied, but not required by this proposal. For example, Fedora has long placed /home on a separate subvolume (or file system) so it can be isolated from system root. Likewise, it makes sense to isolate /var/log and possibly /var/lib/libvirt/images so these locations continue to carry forward in time, even if the system root does a rollback.

Feedback

There will be no change to DNF as part of this change proposal. DNF's history will remain in /var until DNF 5. Discussion continues about the effect of a snapshot+rollback regime on DNF history. Relocate DNF history to /usr.

Upstream RPM accepts the change, but institutionally don't like the loss or weakening of a very well known location for the database, and anticipate complaints.

Benefit to Fedora

• Helps align Fedora variants with each other
  • rpm-ostree based systems (including CoreOS, IoT, Silverblue, Kinoite) already use /usr/lib/sysimage for rpmdb.
• Consistency with another RPM-based distro, (open)SUSE have made this change.
• Accounts for various snapshot+rollback regimes, i.e. it's a beneficial change whether Btrfs or device-mapper based.
• Is a preparatory step to support boot-to-snapshot and transactional update methods for dealing with problematic updates and upgrades.

Scope

• Proposal owners:
  • changes in rpm package
    • create the new path
    • create a symlink for the old path pointing to new path
• Other developers:
  • changes in SElinux policy
  • tracking bug for supermin: test if a package has been installed/updated/removed so that we can rebuild our cache
  • tracking bug for libguestfs: build a "phony" Fedora image for testing with a fake RPM database
  • possible bug in DNF when doing dnf list which writes to one or more rpmdb files (these might be file metadata changes not file data changes)

• Release engineering: #Releng issue 10441
• Policies and guidelines: N/A (not needed for this Change)
• Trademark approval: N/A (not needed for this Change)
• Alignment with Objectives:

Upgrade/compatibility impact

Change will be applied to offline upgrades, similar to the RPM sqlite database change. A systemd service will move the rpmdb from /var to /usr, then create a symlink pointing to /usr from /var.

1. Create /usr/lib/sysimage/rpm (rpm package will do this at preinst)
2. Create symlinks in /usr/lib/sysimage/rpm/ pointing to files in /var/lib/rpm/ (rpm package will do this at preinst)
3. Change the dbpath in /usr/lib/rpm/macros to /usr/lib/sysimage/rpm (rpm package will be patched to do this on F36+)
4. Request rpm rebuild the database (done via systemd service)
5. Remove /var/lib/rpm and create a symlink /var/lib/rpm -> /usr/lib/sysimage/rpm (done via systemd service)

How To Test

1. Perform a new clean install, or upgrade a system
2. Check that /var/lib/rpm is a symlink to /usr/lib/sysimage/rpm
3. Check that /usr/lib/sysimage/rpm is populated with at least rpmdb.sqlite, possibly also rpmdb.sqlite-shm and rpmdb.sqlite-wal
4. Confirm rpm -q <package> and/or rpm -qa still work

User Experience

• symlink /var/lib/rpm -> /usr/lib/sysimage/rpm

Otherwise, the change should be invisible to users.

Dependencies

• rpm-ostree probably should make /usr/share/rpm a symlink to /usr/lib/sysimage/rpm, rather than the reverse as it is currently.
• PackageKit might use inotify on /var/lib/rpm need to check if it does and whether it should be changed or add the additional path

Contingency Plan

• Contingency mechanism: Revert the change, try again the next Fedora release.
• Contingency deadline: Beta freeze
• Blocks release? Yes