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93 lines
3.8 KiB
Markdown
93 lines
3.8 KiB
Markdown
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nav_order: 70
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---
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<!-- SPDX-License-Identifier: (CC-BY-SA-3.0 OR GFDL-1.3-or-later) -->
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# OSTree and /var handling
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{: .no_toc }
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1. TOC
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{:toc}
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## Default commit/image /var handling
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As of OSTree 2024.3, when a commit is "deployed" (queued to boot),
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the initial content of `/var` in a commit will be placed into the
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"stateroot" (default `var`) if the stateroot `var` is empty.
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The semantics of this are intended to match that of Docker "volumes";
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consider that ostree systems have the equivalent of
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`VOLUME /var`
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by default.
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It is still strongly recommended to use systemd `tmpfiles.d` snippets
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to populate directory structure and the like in `/var` on firstboot,
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because this is more resilent.
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Even better, use `StateDirectory=` for systemd units.
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## Pitfalls
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On subsequent upgrades, normally `/var` would not be empty anymore
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(as it's typically expected that basics like `/var/tmp` etc. are created,
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if not also other local state such as `/var/log` etc.). Hence,
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*no updates* from the commit/container will be applied.
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To be clear then:
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- Any files which already exist will *not* be updated.
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- Any files which are deleted in the new version will not be deleted on existing systems.
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## Examples
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### debs/RPMs which drop files into `/opt` (i.e. `/var/opt`)
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The default OSTree "strict" layout has `/opt` be a symlink to `/var/opt`.
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Including any packaged content that "straddles" `/usr` and `/var` (i.e. `/var/opt`)
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will over time cause drift because changes in the package will not be reflected on disk.
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For situations like this, it's strongly recommended to enable either
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`composefs.enabled = true` or the `root.transient = true` option for `ostree-prepare-root.conf`
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and change ensure your commit/container image has `/opt` as a plain directory. In the former case,
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content in `/opt` will be immutable at runtime, the same as everything else in `/usr`.
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In the latter case content it will be writable but transient.
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There's also a currently-experimental [../man/ostree-state-overlay@.service.xml](ostree-state-overlay@.service)
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which can manage stateful writable overlays for individual mounts.
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### Apache default content in `/var/www/html`
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In general, such static content would much better live in `/usr` - or even better, in an application container.
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### User home directories and databases
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The semantics here are likely OK for the use case of "default users".
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### `/var/lib/containers`
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Pulling container images into OSTree commits like this would be a bad idea; similar problems as RPM content.
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### dnf `/var/lib/dnf/history.sqlite`
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For $reasons dnf has its own database for state distinct from the RPM database, which on rpm-ostree systems is in `/usr/share/rpm` (under the read-only bind mount, managed by OS updates).
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In an image/container-oriented flow, we don't really care about this database which mainly holds things like "was this package user installed". This data could move to `/usr`.
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## Previous ostree /var and tmpfiles.d /usr/share/factory/var
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From OSTree versions 2023.8 to v2024.3 the `/usr/lib/tmpfiles.d/ostree-tmpfiles.conf` file included this snippet:
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```text
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# Automatically propagate all /var content from /usr/share/factory/var;
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# the ostree-container stack is being changed to do this, and we want to
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# encourage ostree use cases in general to follow this pattern.
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C+! /var - - - - -
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```
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Until version 0.13.2 of the ostree-ext project, content in `/var` in fetched container images is moved to `/usr/share/factory/var`, but this no longer happens when targeting ostree v2024.3.
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Together, this will have the semantic that on OS updates, on the next boot (early in boot), any new files/directories will be copied. For more information on this, see [`man tmpfiles.d`](https://man7.org/linux/man-pages/man5/tmpfiles.d.5.html).
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This has been reverted, and the semantics defer to the above ostree semantic.
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