diff --git a/man/ostree-prepare-root.xml b/man/ostree-prepare-root.xml index 70371b7bc5..a92ad79907 100644 --- a/man/ostree-prepare-root.xml +++ b/man/ostree-prepare-root.xml @@ -120,20 +120,24 @@ License along with this library. If not, see . root.transient A boolean value; the default is false. - If this is set to true, then the / filesystem will be a writable overlayfs, - with the upper directory being a hidden directory (in the underlying system root filesystem) that will persist across reboots by default. - However, changes will be discarded on OS updates! + Setting this flag to true requires composefs (See composefs.enabled). + When enabled, the root mount point / will be an overlayfs whose contents will be stored + in a tmpfs, and hence discarded on OS upgrade or reboot. - Enabling this option can be very useful for cases such as packages (dpkg/rpm/etc) that write content into /opt, - particularly where they expect the target to be writable at runtime. To make that work, ensure that your /opt - directory is *not* a symlink to /var/opt, but is just an empty directory. - - - Note the /usr mount point remains read-only by default. This option is independent of etc.transient and sysroot.readonly; + This option is independent of etc.transient and sysroot.readonly; it is supported for example to have root.transient=true but etc.transient=false in which case changes to /etc continue to persist across updates, with the default OSTree 3-way merge applied. - + Also related to persistence it is important to emphasize that /sysroot (the physical root filesystem) is still persistent + by default; in-place OS upgrades can be applied. + + + Enabling this option can make it significantly easier to adopt an image-based model in some circumstances. + For example, if you have a configuration management system that is inspecting machine-specific state and + e.g. dynamically installing packages or applying configuration, it can more easily be adapted to + run on each boot, while still shifting a portion (or ideally most) image configuration to build time + as part of the base image/commit. + composefs.enabled