Concepts in Action
Now that we have a fresh installed host (either as [[default|Photon-RPM-OSTree:-2-Installing-a-host-against-default-server-repository]] or [[custom|Photon-RPM-OSTree:-7-Installing-a-host-against-a-custom-server-repository]]), I can explain better the OStree concepts and see them in action.
Querying the deployed filetrees
The first thing to do is to run a command that tells us what is installed on the machine and when. Since it's a fresh install from the CD, there is only one bootable filetree image deployed.
root@photon-host [ ~ ]# rpm-ostree status * ostree://photon:photon/3.0/x86_64/minimal Version: 3.0_minimal (2019-08-29T11:20:19Z) Commit: a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84f20833650
Bootable filetree version
3.0_minimal is not the Linux Photon OS release version, nor daily build, but rather a human readable, self-incrementing version associated with every commit that brings file/package updates. Think of this as version 0. The following versions are going to be 3.0_minimal.1, 3.0_minimal.2, 3.0_minimal.3 and so on.
The ID listed is actually the first 5 bytes (10 hex digits) of the commit hash. If you want to see the verbose mode, use the
root@photon-host [ ~ ]# rpm-ostree status -v State: idle AutomaticUpdates: disabled Deployments: * ostree://photon:photon/3.0/x86_64/minimal Version: 3.0_minimal (2019-08-29T11:20:19Z) Commit: a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84f20833650 `- photon (2019-08-29T11:18:53Z) Staged: no StateRoot: photon
RPM OStree Options
To see the list of options available with the rpm-ostree command, use the -h option.
root@photon-host [ ~ ]# rpm-ostree -h Usage: rpm-ostree [OPTION?] COMMAND Builtin Commands: compose Commands to compose a tree cleanup Clear cached/pending data db Commands to query the RPM database deploy Deploy a specific commit rebase Switch to a different tree rollback Revert to the previously booted tree status Get the version of the booted system upgrade Perform a system upgrade reload Reload configuration usroverlay Apply a transient overlayfs to /usr cancel Cancel an active transaction initramfs Enable or disable local initramfs regeneration install Overlay additional packages uninstall Remove overlayed additional packages override Manage base package overrides reset Remove all mutations refresh-md Generate rpm repo metadata kargs Query or modify kernel arguments Help Options: -h, --help Show help options Application Options: --version Print version information and exit
The OS Name identifies the operating system installed. All bootable filetrees for the same OS will share the /var directory, in other words applications installed in one booted image into this directory will be available in all other images.
If a new set of images are created for a different OS, they will receive a fresh copy of /var that is not shared with the previous OS images for the initial OS. In other words, if a machine is dual boot for different operating systems, they will not share each other's /var content, however they will still merge 3-way /etc.
The Refspec is a branch inside the repo, expressed in a hierarchical way. In this case, it's the default branch that will receive package updates for the Photon OS 1.0 Minimal installation profile on Intel platforms. There could be other branches in the future, for example photon/3.0/x86_64/full that will match the Full installation profile (full set of packages installed).
Think of Refspec as the head of the minimal branch (just like in git) at the origin repo. On the replicated, local repo at the host, minimal is a file that contains the latest commit ID known for that branch.
root@photon-host [ ~ ]# cat /ostree/repo/refs/remotes/photon/photon/3.0/x86_64/minimal a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84f20833650
Why are there two 'photon' directory levels in the remotes path? The photon: prefix in the Refspec listed by
rpm-ostree status corresponds to the first photon directory in the remotes path and is actually the name given to the remote that the host is connected to, which points to an http or https URL. We'll talk about remotes later, but for now think of it as a namespace qualifier. The second photon is part of the Refspec path itself.
We've used so far
rpm-ostree. The same information can be obtained running an
root@photon-host [ ~ ]# ostree admin status * photon a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84f20833650.0 Version: 3.0_minimal origin refspec: photon:photon/3.0/x86_64/minimal
But where is this information stored? As you may have guessed, the local repo stores the heads of the deployed trees - the most recent commitment ID, just like Git does:
root@photon-host [ ~ ]# cat /ostree/repo/refs/heads/ostree/0/1/0 a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84f20833650
This also where this command that lists the references (local heads and remotes) takes its data from:
root@photon-host [ ~ ]# ostree refs ostree/0/1/0 photon:photon/3.0/x86_64/minimal
Based on that, it could find the root of the deployment that it boots from. The actual filetree is deployed right here:
root@photon-host [ ~ ]# ls -l /ostree/deploy/photon/deploy/a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84f20833650.0 total 36 lrwxrwxrwx 2 root root 7 Sep 4 04:58 bin -> usr/bin drwxr-xr-x 2 root root 4096 Jan 1 1970 boot drwxr-xr-x 2 root root 4096 Jan 1 1970 dev drwxr-xr-x 34 root root 4096 Sep 4 05:00 etc lrwxrwxrwx 2 root root 8 Sep 4 04:58 home -> var/home lrwxrwxrwx 3 root root 7 Sep 4 04:58 lib -> usr/lib lrwxrwxrwx 3 root root 7 Sep 4 04:58 lib64 -> usr/lib lrwxrwxrwx 2 root root 9 Sep 4 04:58 media -> run/media lrwxrwxrwx 2 root root 7 Sep 4 04:58 mnt -> var/mnt lrwxrwxrwx 2 root root 7 Sep 4 04:58 opt -> var/opt lrwxrwxrwx 2 root root 14 Sep 4 04:58 ostree -> sysroot/ostree drwxr-xr-x 2 root root 4096 Jan 1 1970 proc lrwxrwxrwx 2 root root 12 Sep 4 04:58 root -> var/roothome drwxr-xr-x 2 root root 4096 Jan 1 1970 run lrwxrwxrwx 2 root root 8 Sep 4 04:58 sbin -> usr/sbin lrwxrwxrwx 2 root root 7 Sep 4 04:58 srv -> var/srv drwxr-xr-x 2 root root 4096 Jan 1 1970 sys drwxr-xr-x 2 root root 4096 Jan 1 1970 sysroot lrwxrwxrwx 2 root root 11 Sep 4 04:58 tmp -> sysroot/tmp drwxr-xr-x 10 root root 4096 Jan 1 1970 usr drwxr-xr-x 8 root root 4096 Sep 4 04:59 var
So how is a deployment linked to a specific branch, originating from a remote repo? Well, there is a file next to the deployed filetree root directory with the same name and .origin suffix, that contains exactly this info:
root@photon-host [ ~ ]# cat /ostree/deploy/photon/deploy/a31a843985e314a9e70bcf09afe8d59f7351817d9fb743c2b6dab84 f20833650.0.origin [origin] refspec=photon:photon/3.0/x86_64/minimal
Fast forwarding a bit, if there is a new deployment due to an upgrade or rebase, a new filetree will be added at the same level, and a new .origin file will tie it to the remote branch it originated from.
The photon directory in the path is the actual OSname. Multiple deployments of same OS will share a writable /var folder.
root@photon-host [ ~ ]# ls -l /ostree/deploy/photon/var/ total 52 drwxr-xr-x 4 root root 4096 Sep 4 05:00 cache drwxr-xr-x 2 root root 4096 Sep 4 05:00 home drwxr-xr-x 14 root root 4096 Sep 4 05:00 lib drwxr-xr-x 2 root root 4096 Sep 4 05:00 local lrwxrwxrwx 1 root root 11 Sep 4 04:59 lock -> ../run/lock drwxr-xr-x 4 root root 4096 Sep 4 05:00 log drwxr-xr-x 2 root root 4096 Sep 4 05:00 mail drwxr-xr-x 2 root root 4096 Sep 4 05:00 mnt drwxr-xr-x 4 root root 4096 Sep 4 05:00 opt drwx------ 3 root root 4096 Sep 4 05:25 roothome lrwxrwxrwx 1 root root 6 Sep 4 04:59 run -> ../run drwxr-xr-x 2 root root 4096 Sep 4 05:00 spool drwxr-xr-x 2 root root 4096 Sep 4 05:00 srv drwxrwxrwt 5 root root 4096 Sep 4 05:34 tmp drwxr-xr-x 11 root root 4096 Sep 4 05:00 usrlocal