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Since I struggled to understand and find information about how to troubleshoot a running linuxkit instance, I propose to add these two FAQ entries. The first one explains why it is possible to not see the `containerd` or `init` outputs at boot in the console. The second one gives a few `ctr` example to list containers, running containers or how to open a shell in a given container. Signed-off-by: Brice Figureau <brice@daysofwonder.com>
79 lines
3.1 KiB
Markdown
79 lines
3.1 KiB
Markdown
# FAQ
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Please open an issue if you want to add a question here.
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## How do updates work?
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LinuxKit does not require being installed on a disk, it is often run from an ISO, PXE or other
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such means, so it does not require an on disk upgrade method such as the ChromeOS code that
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is often used. It would definitely be possible to use that type of upgrade method if the
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system is installed, and it would be useful to support this for that use case, and an
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updater container to control this for people who want to use this.
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We generally use external tooling such as [Infrakit](https://github.com/docker/infrakit) or
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CloudFormation templates to manage the update process externally from LinuxKit, including
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doing rolling cluster upgrades to make sure distributed applications stay up and responsive.
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Updates may preserve the state disk used by applications if needed, either on the same physical
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node, or by reattaching a virtual cloud volume to a new node.
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## What do I need to build LinuxKit?
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We have tried to make this as simple as possible, by using containers for the build process, so
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you should be able to build LinuxKit on any OSX or Linux laptop; we should have Windows build support
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soon.
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## Why not use `systemd`?
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In order to keep the system minimal, `systemd` did not seem appropriate, as it brings in a lot
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of dependencies and functionality that we do not need. At present we are using the `busybox`
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`init` process, and a small set of minimal scripts, but we expect to replace that with a small
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standalone `init` process and a small piece of code to bring up the system containers where the
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real work takes place.
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## Console not displaying init or containerd output at boot
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If you're not seeing `containerd` logs in the console during boot, make sure that your kernel `cmdline` configuration doesn't list multiple consoles.
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`init` and other processes like `containerd` will use the last defined console in the kernel `cmdline`. When using `qemu`, to see the console you need to list `ttyS0` as the last console to properly see the output.
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## Troubleshooting containers
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Linuxkit runs all services in a specific `containerd` namespace called `services.linuxkit`. To list all the defined containers:
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```sh
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(ns: getty) linuxkit-befde23bc535:~# ctr -n services.linuxkit container ls
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CONTAINER IMAGE RUNTIME
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getty - io.containerd.runtime.v1.linux
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```
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To list all running containers and their status:
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```sh
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(ns: getty) linuxkit-befde23bc535:~# ctr -n services.linuxkit task ls
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TASK PID STATUS
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getty 661 RUNNING
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```
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To list all processes running in a container:
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```sh
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(ns: getty) linuxkit-befde23bc535:/containers/services/getty# ctr -n services.linuxkit task ps getty
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PID INFO
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661 &ProcessDetails{ExecID:getty,}
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677 -
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685 -
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686 -
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687 -
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1237 -
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```
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To attach a shell to a running container:
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```sh
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(ns: getty) linuxkit-befde23bc535:/containers/services/getty# ctr -n services.linuxkit tasks exec --tty --exec-id sh sshd /bin/ash -l
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(ns: sshd) linuxkit-befde23bc535:/#
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```
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Containers are defined as OCI bundles in `/containers`.
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