rpm-ostree/doc/administrator-handbook.md

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## Administering an rpm-ostree based system
At the moment, there are three primary commands to be familiar with on
an rpm-ostree based system. Remember that `atomic` is an alias for
`rpm-ostree`. The author tends to use the former on client systems,
and the latter on compose servers.
# atomic status
Will show you your deployments, in the order in which they will appear
in the bootloader. The `*` shows the currently booted deployment.
# atomic upgrade
Will perform a system upgrade, creating a *new* chroot, and set it as
the default for the next boot. You should use `systemctl reboot`
shortly afterwards.
# atomic rollback
By default, the `atomic upgrade` will keep at most two bootable
"deployments", though the underlying technology supports more.
## Filesystem layout
The only writable directories are `/etc` and `/var`. In particular,
`/usr` has a read-only bind mount at all times. Any data in `/var` is
never touched, and is shared across upgrades.
At upgrade time, the process takes the *new default* `/etc`, and adds
your changes on top. This means that upgrades will receive new
default files in `/etc`, which is quite a critical feature.
## Operating system changes
* The RPM database is stored in `/usr/share/rpm`, and is immutable.
* A package [nss-altfiles](https://github.com/aperezdc/nss-altfiles) is required,
and the system password database is stored in `/usr/lib/passwd`. Similar
for the group database.