Add in OS Docs

2026-05-22 21:05:13 +00:00 · 2018-04-16 11:21:03 -07:00
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+---
+tag: ["rancheros", "os"]
+category: "os"
+layout: list-docs
+title: Adding Kernel Parameters
+weight: 133
+---
+
+## Kernel boot parameters
+
+RancherOS parses the Linux kernel boot cmdline to add any keys it understands to its configuration. This allows you to modify what cloud-init sources it will use on boot, to enable `rancher.debug` logging, or to almost any other configuration setting.
+
+There are two ways to set or modify persistent kernel parameters, in-place (editing the file and reboot) or during installation to disk.
+
+### In-place editing
+
+_As of v1.1+_
+To edit the kernel boot parameters of an already installed RancherOS system, use the new `sudo ros config syslinux` editing command (uses `vi`).
+
+> To activate this setting, you will need to reboot.
+
+_For v1.0_
+
+For in-place editing, you will need to run a container with an editor and a mount to access the `/boot/global.cfg` file containing the kernel parameters.
+
+> To activate this setting, you will need to reboot.
+
+```bash
+$ sudo system-docker run --rm -it -v /:/host alpine vi /host/boot/global.cfg
+```
+
+### During installation
+
+If you want to set the extra kernel parameters when you are [Installing RancherOS to Disk]({{page.osbaseurl}}/running-rancheros/server/install-to-disk/) please use the `--append` parameter.
+
+```bash
+$ sudo ros install -d /dev/sda --append "rancheros.autologin=tty1"
+```
+
+_As of v1.1_
+
+### Graphical boot screen
+
+RancherOS v1.1.0 added a Syslinux boot menu, which allows you to temporarily edit the boot paramters, or to select "Debug logging", "Autologin", both "Debug logging & Autologin" and "Recovery Console".
+
+On desktop systems the Syslinux boot menu can be switched to graphical mode by adding `UI vesamenu.c32` to a new line in `global.cfg` (use `sudo ros config syslinux` to edit the file).
+
+### Useful RancherOS cloud-init or boot settings
+
+#### Recovery console
+
+`rancher.recovery=true` will start a single user `root` bash session as easily in the boot process, with no network, or persitent filesystem mounted. This can be used to fix disk problems, or to debug your system.
+
+#### Enable/Disable sshd
+
+`rancher.ssh.daemon=false` (its enabled in the os-config) can be used to start your RancherOS with no sshd daemon. This can be used to further reduce the ports that your system is listening on.
+
+#### Enable debug logging
+
+`rancher.debug=true` will log everything to the console for debugging.
+
+#### Autologin console
+
+`rancher.autologin=<tty...>` will automatically log in the sepcified console - common values are `tty1`, `ttyS0` and `ttyAMA0` - depending on your platform.
+
+#### Enable/Disable hypervisor service auto-enable
+
+RancherOS v1.1.0 added detection of Hypervisor, and then will try to download the a service called `<hypervisor>-vm-tools`. This may cause boot speed issues, and so can be disabled by setting `rancher.hypervisor_service=false`.