shaba/ostree
1
0
Fork 0
mirror of https://github.com/ostreedev/ostree.git synced 2024-12-22 17:35:55 +03:00
Code Issues Projects Releases Wiki Activity

docs/var: Update for latest

Browse Source 
This reorients things here around the latest `VOLUME /var` approach.
This commit is contained in:
Colin Walters 2024-02-12 11:59:39 -05:00
parent 87dcc801a2
commit 6df18abee7
1 changed files with 40 additions and 34 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

74
docs/var.md
View File

@ -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.