From 566e4b3a19e8cba2fee588b101560269b8dae033 Mon Sep 17 00:00:00 2001 From: Kai Lueke Date: Fri, 22 Jul 2022 15:03:12 +0200 Subject: [PATCH 1/2] man: Do not recommend to overlay files with sysext even if possible While overlaying files with a sysext can be useful, it may lead to unexpected problems depending on when a process got started and which version of the file it gets. Call out that overlaying files is possible but don't recommend to make use of it. --- man/systemd-sysext.xml | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/man/systemd-sysext.xml b/man/systemd-sysext.xml index 60ae4aa8bf..d7f5d2f37f 100644 --- a/man/systemd-sysext.xml +++ b/man/systemd-sysext.xml @@ -64,7 +64,7 @@ System extensions are supposed to be purely additive, i.e. they are supposed to include only files that do not exist in the underlying basic OS image. However, the underlying mechanism (overlayfs) also - allows removing files, but it is recommended not to make use of this. + allows overlaying or removing files, but it is recommended not to make use of this. System extension images may be provided in the following formats: From 519c2f0d6b343d140f7e08e3eb0f46708c023b4a Mon Sep 17 00:00:00 2001 From: Kai Lueke Date: Fri, 22 Jul 2022 15:09:21 +0200 Subject: [PATCH 2/2] man: Document mask workaround for sysext images A read-only /usr may ship a sysext image by default and the user wants to opt out. Currently it's not clear how to do this. Document that a /dev/null symlink in /etc/extensions/ works to "mask" a sysext image in a folder with lower precedence. --- man/systemd-sysext.xml | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/man/systemd-sysext.xml b/man/systemd-sysext.xml index d7f5d2f37f..42e8e12df9 100644 --- a/man/systemd-sysext.xml +++ b/man/systemd-sysext.xml @@ -108,7 +108,9 @@ accessed. Note that there is no concept of enabling/disabling installed system extension images: all - installed extension images are automatically activated at boot. + installed extension images are automatically activated at boot. However, you can place a symlink + to /dev/null in /etc/extensions/ to "mask" an image with + the same name in a folder with lower precedence. A simple mechanism for version compatibility is enforced: a system extension image must carry a /usr/lib/extension-release.d/extension-release.$name