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blog: Add one for transient root with composefs #42

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blog: Add one for transient root with composefs
cgwalters Jun 5, 2026
944f2f1
blog: Fix broken link in sealed-images-building post
cgwalters Jun 5, 2026
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3 changes: 3 additions & 0 deletions config.toml
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Expand Up @@ -71,3 +71,6 @@ footer = ""

[extra.authors.jeckersb]
name = "John Eckersberg"

[extra.authors.cgwalters]
name = "Colin Walters"
34 changes: 34 additions & 0 deletions content/blog/2026-jun-05-transient-root-etc-var.md
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+++
title = "Video: sealed bootc with transient /etc and /var"
date = 2026-06-05
slug = "2026-jun-05-transient-root-etc-var"

[extra]
author = "cgwalters"
+++

# Video: sealed bootc with transient /etc and /var

I recorded a short demo of the new composefs mount configuration
support that landed in [bootc#2201](https://github.com/bootc-dev/bootc/pull/2201).

[![Video: sealed bootc with transient /etc and /var](https://img.youtube.com/vi/VJYLtUOCqgA/0.jpg)](https://youtu.be/VJYLtUOCqgA)

The PR adds a `/usr/lib/bootc/setup-root-conf.toml` file that image
authors can ship in their container image to control how the
composefs-backed root filesystem is mounted at boot:

- `[root] transient = true` wraps the composefs lower in a tmpfs
overlay, so all writes to `/` are discarded on reboot.
- `[etc] mount = "transient"|"overlay"|"bind"|"none"` controls how
`/etc` is mounted from the deployment state directory.
- `[var] mount = "none"|"bind"` controls whether `/var` is
bind-mounted from persistent state. When set to `none`, `/var` is left as an
empty composefs directory, and `systemd.volatile=state` on the
kernel command line causes bootc to automatically skip the bind-mount
so systemd can place a fresh tmpfs there.

This builds directly on the
[sealed images series](@/blog/2026-may-04-sealed-images-security-chain.md):
with a transient root and `/etc`, each boot starts from a clean,
verified image with no persistent mutation to the OS layer.
3 changes: 1 addition & 2 deletions content/blog/2026-may-06-sealed-images-building.md
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Expand Up @@ -180,8 +180,7 @@ $ just build # build the sealed image

## Secret handling in CI

The examples repository includes a
[GitHub Actions workflow](https://github.com/redhat-cop/rhel-bootc-examples/blob/main/sealing/.github/workflows/build-sealed.yml)
The examples repository includes a GitHub Actions workflow
that demonstrates how to handle key material in CI. The db private
key is stored as a GitHub Actions secret and written to a temporary
file during the build.
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