From 6df18abee7521d872fe12fe37c030033b2a4e171 Mon Sep 17 00:00:00 2001 From: Colin Walters Date: Mon, 12 Feb 2024 11:59:39 -0500 Subject: [PATCH] docs/var: Update for latest This reorients things here around the latest `VOLUME /var` approach. --- docs/var.md | 74 +++++++++++++++++++++++++++++------------------------ 1 file changed, 40 insertions(+), 34 deletions(-) diff --git a/docs/var.md b/docs/var.md index 61480d8c..62535989 100644 --- a/docs/var.md +++ b/docs/var.md @@ -26,54 +26,43 @@ because this is more resilent. Even better, use `StateDirectory=` for systemd units. -### ostree container /var - -Some earlier versions of the ostree-container stack migrated content in `/var` -in container images into `/usr/share/factory/var` (per below). This has -been reverted, and the semantics defer to the above ostree semantic. - -## Previous /var handling via /usr/share/factory/var - -As of OSTree 2023.8, the `/usr/lib/tmpfiles.d/ostree-tmpfiles.conf` file gained this snippet: - -```text -# Automatically propagate all /var content from /usr/share/factory/var; -# the ostree-container stack is being changed to do this, and we want to -# encourage ostree use cases in general to follow this pattern. -C+! /var - - - - - -``` - -This is inert by default. As of version 0.13 of the ostree-ext project, content in `/var` in fetched container images is moved to `/usr/share/factory/var`. This is no longer recommended. - -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). - -However, `tmpfiles.d` is not a package system: - ## Pitfalls -- Large amounts of data will slow down firstboot while the content is copied (though reflinks are used if available) +On subsequent upgrades, normally `/var` would not be empty anymore +(as it's typically expected that basics like `/var/tmp` etc. are created, + if not also other local state such as `/var/log` etc.). Hence, +*no updates* from the commit/container will be applied. + +To be clear then: + - Any files which already exist will *not* be updated. - Any files which are deleted in the new version will not be deleted on existing systems. ## Examples +### debs/RPMs which drop files into `/opt` (i.e. `/var/opt`) + +The default OSTree "strict" layout has `/opt` be a symlink to `/var/opt`. +Including any packaged content that "straddles" `/usr` and `/var` (i.e. `/var/opt`) +will over time cause drift because changes in the package will not be reflected on disk. + +For situations like this, it's strongly recommended to enable either +`composefs.enabled = true` or the `root.transient = true` option for `ostree-prepare-root.conf` +and change ensure your commit/container image has `/opt` as a plain directory. In the former case, +content in `/opt` will be immutable at runtime, the same as everything else in `/usr`. +In the latter case content it will be writable but transient. + +There's also a currently-experimental [../man/ostree-state-overlay@.service.xml](ostree-state-overlay@.service) +which can manage stateful writable overlays for individual mounts. + ### Apache default content in `/var/www/html` -The `tmpfiles.d` model may work OK for use cases that wants to treat this content as locally mutable state. But in general, such static content would much better live in `/usr` - or even better, in an application container. +In general, such static content would much better live in `/usr` - or even better, in an application container. ### User home directories and databases The semantics here are likely OK for the use case of "default users". -### debs/RPMs which drop files into `/opt` (i.e. `/var/opt`) - -The default OSTree "strict" layout has `/opt` be a symlink to `/var/opt`. -However, `tmpfiles.d` is not a package system, and so over time these will slowly -break because changes in the package will not be reflected on disk. - -For situations like this, it's recommended to enable the `root.transient = true` option for `ostree-prepare-root.conf` -and change your build system to make `/opt` a plain directory. - ### `/var/lib/containers` Pulling container images into OSTree commits like this would be a bad idea; similar problems as RPM content. @@ -83,3 +72,20 @@ Pulling container images into OSTree commits like this would be a bad idea; simi 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). 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`. + +## Previous ostree /var and tmpfiles.d /usr/share/factory/var + +From OSTree versions 2023.8 to v2024.3 the `/usr/lib/tmpfiles.d/ostree-tmpfiles.conf` file included this snippet: + +```text +# Automatically propagate all /var content from /usr/share/factory/var; +# the ostree-container stack is being changed to do this, and we want to +# encourage ostree use cases in general to follow this pattern. +C+! /var - - - - - +``` + +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. + +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). + +This has been reverted, and the semantics defer to the above ostree semantic.