Ubuntu 26.04 LTS: Three Breaking Changes You Must Prepare For

Overview

Ubuntu 26.04 LTS (Resolute Raccoon) deliberately removes several legacy features, turning the upgrade into a forced migration rather than an optional enhancement. Three major changes have no rollback path: cgroup v1 is dropped, sudo is replaced by sudo‑rs (a Rust implementation), and GNU coreutils are replaced by the Rust‑based uutils/coreutils.

cgroup v1 Removal

systemd 259, shipped with Ubuntu 26.04, eliminates all cgroup v1 support. The upgrade tool checks for cgroup v1 usage and aborts if it is still present. Environments still using Docker < 20.10, older Kubernetes kubelet configurations, or LXC/LXD containers that mount cgroup v1 will fail to start.

To remediate, administrators should verify the current cgroup version with cat /proc/cgroups or mount | grep cgroup, update container runtimes to use cgroup v2, and test each workload on a temporary VM. This typically requires an afternoon for a single server and a sprint for a Kubernetes cluster.

sudo Rewritten in Rust (sudo‑rs)

Canonical now ships sudo‑rs as the default sudo provider. The command syntax, sudoers file format, and supported flags remain the same, but the binary is different. The most visible change is password feedback: asterisks are shown by default, which can be disabled with Defaults !pwfeedback.

Compatibility concerns include the lack of support for sudo plugins, LDAP‑based sudoers, I/O logging, and sendmail integration. Enterprise environments relying on these features will see clear error messages, but the upgrade will halt any automated sudo calls until the issues are addressed.

GNU coreutils Replaced by uutils/coreutils

Ubuntu 26.04 replaces traditional GNU coreutils (ls, cp, mv, cat, date, sort, etc.) with the Rust‑based uutils/coreutils 0.7.0. While most commands behave similarly, edge‑case differences exist—for example, the Rust date command initially omitted the -r flag, breaking tools like unattended‑upgrades.

The uutils project reports 94.59% compatibility with the GNU test suite, but even a 5% failure rate can cause widespread issues across many servers. Administrators should test scripts that parse coreutils output, especially those using ls, sort, date, or cp, before upgrading.

APT 3.1 and GNOME 50 Changes

APT 3.1 removes apt-key, requiring the use of signed‑by in source lists. The transition period ends with Ubuntu 26.04, so any third‑party repositories added via apt-key add must be migrated.

GNOME 50 drops X11 sessions from GDM; only Wayland (or XWayland) is available. Users relying on the “Ubuntu on Xorg” session, particularly those with NVIDIA proprietary drivers, need to verify Wayland compatibility before the upgrade.

Impact Matrix

The three breaking changes affect most system types, with cgroup v1 removal impacting container workloads, sudo‑rs affecting privileged automation, and coreutils replacement affecting scripts and CI/CD pipelines. A concise impact matrix can be visualized as follows:

Containers & Kubernetes – cgroup v1

Enterprise automation – sudo‑rs

Shell scripts & CI/CD – coreutils

Migration Checklist (Before April 23)

Week 1 – Audit : Run cat /proc/cgroups on every server, list all third‑party sources using apt-key, and identify scripts that parse coreutils output.

Week 2 – Resolve Blockers : Migrate cgroup v1 to v2, replace apt-key entries with signed‑by, and test sudo‑rs with your PAM configuration on a temporary VM.

Week 3 – Validate : Execute your CI/CD pipelines against an Ubuntu 26.04 test environment, compare coreutils outputs, and verify Wayland support for desktop users.

Week 4 – Upgrade Staging : Run a full production‑like workload for at least one work week in a pre‑production environment before touching production.

Skipping any of these steps will likely result in broken services after the upgrade, as Ubuntu 26.04 is the first LTS that refuses to upgrade an unready system.

Long‑Term Support Considerations

Ubuntu Pro extends support for up to 15 years, meaning 26.04 could be in production until 2041. Ensure your infrastructure can remain compatible for the long term before committing.