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Early cloud-init
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Josh Curl
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docs/os/boot-process/built-in-system-services/index.md
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docs/os/boot-process/built-in-system-services/index.md
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---
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title: Built-in System Services in RancherOS
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layout: os-default
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redirect_from:
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- os/system-services/built-in-system-services/
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---
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## Built-in System Services
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To launch RancherOS, we have built-in system services. They are defined in the [Docker Compose](https://docs.docker.com/compose/compose-file/) format, and can be found in the default system config file, `/usr/share/ros/os-config.yml`. You can [add your own system services]({{site.baseurl}}/os/system-services/) or override services in the cloud-config.
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### preload-user-images
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Read more about [image preloading]({{site.baseurl}}/os/boot-process/image-preloading/).
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### network
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During this service, networking is set up, e.g. hostname, interfaces, and DNS.
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It is configured by `hostname` and `rancher.network`[settings]({{site.baseurl}}/os/networking/) in [cloud-config]({{site.baseurl}}/os/configuration/#cloud-config).
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### ntp
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Runs `ntpd` in a System Docker container.
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### console
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This service provides the RancherOS user interface by running `sshd` and `getty`. It completes the RancherOS configuration on start up:
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1. If the `rancher.password=<password>` kernel parameter exists, it sets `<password>` as the password for the `rancher` user.
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2. If there are no host SSH keys, it generates host SSH keys and saves them under `rancher.ssh.keys` in [cloud-config]({{site.baseurl}}/os/configuration/#cloud-config).
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3. Runs `cloud-init -execute`, which does the following:
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* Updates `.ssh/authorized_keys` in `/home/rancher` and `/home/docker` from [cloud-config]({{site.baseurl}}/os/configuration/ssh-keys/) and metadata.
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* Writes files specified by the `write_files` [cloud-config]({{site.baseurl}}/os/configuration/write-files/) setting.
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* Resizes the device specified by the `rancher.resize_device` [cloud-config]({{site.baseurl}}/os/configuration/resizing-device-partition/) setting.
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* Mount devices specified in the `mounts` [cloud-config]({{site.baseurl}}/os/configuration/additional-mounts/) setting.
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* Set sysctl parameters specified in the`rancher.sysctl` [cloud-config]({{site.baseurl}}/os/configuration/sysctl/) setting.
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4. If user-data contained a file that started with `#!`, then a file would be saved at `/var/lib/rancher/conf/cloud-config-script` during cloud-init and then executed. Any errors are ignored.
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5. Runs `/opt/rancher/bin/start.sh` if it exists and is executable. Any errors are ignored.
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6. Runs `/etc/rc.local` if it exists and is executable. Any errors are ignored.
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### docker
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This system service runs the user docker daemon. Normally it runs inside the console system container by running `docker-init` script which, in turn, looks for docker binaries in `/opt/bin`, `/usr/local/bin` and `/usr/bin`, adds the first found directory with docker binaries to PATH and runs `dockerlaunch docker daemon` appending the passed arguments.
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Docker daemon args are read from `rancher.docker.args` cloud-config property (followed by `rancher.docker.extra_args`).
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docs/os/boot-process/cloud-init/index.md
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docs/os/boot-process/cloud-init/index.md
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---
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title: Cloud-init
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layout: os-default
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---
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## Cloud-init
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Userdata and metadata can be fetched from a cloud provider, VM runtime, or management service during the RancherOS boot process. Since v0.8.0, this process occurs while RancherOS is still running from memory and before System Docker starts. It is configured by the `rancher.cloud_init.datasources` configuration parameter. For cloud-provider specific images, such as AWS and GCE, the datasource is pre-configured.
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### Userdata
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Userdata is a file given by users when launching RancherOS hosts. It is stored in different locations depending on its format. If the userdata is a [cloud-config]({{site.baseurl}}/os/configuration/#cloud-config) file, indicated by beginning with `#cloud-config` and being in YAML format, it is stored in `/var/lib/rancher/conf/cloud-config.d/boot.yml`. If the userdata is a script, indicated by beginning with `#!`, it is stored in `/var/lib/rancher/conf/cloud-config-script`.
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### Metadata
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Although the specifics vary based on provider, a metadata file will typically contain information about the RancherOS host and contain additional configuration. Its primary purpose within RancherOS is to provide an alternate source for SSH keys and hostname configuration. For example, AWS launches hosts with a set of authorized keys and RancherOS obtains these via metadata. Metadata is stored in `/var/lib/rancher/conf/metadata`.
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## Configuration Load Order
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[Cloud-config]({{site.baseurl}}/os/configuration/#cloud-config/) is read by system services when they need to get configuration. Each additional file overwrites and extends the previous configuration file.
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1. `/usr/share/ros/os-config.yml` - This is the system default configuration, which should **not** be modified by users.
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2. `/usr/share/ros/oem/oem-config.yml` - This will typically exist by OEM, which should **not** be modified by users.
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3. Files in `/var/lib/rancher/conf/cloud-config.d/` ordered by filename. If a file is passed in through user-data, it is written by cloud-init and saved as `/var/lib/rancher/conf/cloud-config.d/boot.yml`.
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4. `/var/lib/rancher/conf/cloud-config.yml` - If you set anything with `ros config set`, the changes are saved in this file.
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5. Kernel parameters with names starting with `rancher`.
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6. `/var/lib/rancher/conf/metadata` - Metadata added by cloud-init.
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docs/os/boot-process/image-preloading/index.md
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docs/os/boot-process/image-preloading/index.md
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---
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title: Image Preloading
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layout: os-default
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redirect_from:
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- os/configuration/prepacking-docker-images/
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---
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## Image Preloading
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---
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On boot, RancherOS scans `/var/lib/rancher/preload/docker` and `/var/lib/rancher/preload/system-docker` directories and tries to load container image archives it finds there, with `docker load` and `system-docker load`.
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The archives are `.tar` files, optionally compressed with `xz` or `gzip`. These can be produced by `docker save` command, e.g.:
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```
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$ docker save my-image1 my-image2 some-other/image3 | xz > my-images.tar.xz
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```
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The resulting files should be placed into `/var/lib/rancher/preload/docker` or `/var/lib/rancher/preload/system-docker` (depending on whether you want it preloaded into Docker or System Docker).
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Pre-loading process only reads each new archive once, so it won't take time on subsequent boots (`<archive>.done` files are created to mark the read archives). If you update the archive (place a newer archive with the same name) it'll get read on the next boot as well.
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Pre-packing docker images is handy when you're customizing your RancherOS distribution (perhaps, building cloud VM images for your infrastructure).
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