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Add FAQ entries to help troubleshoot running containers

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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>
This commit is contained in:
Brice Figureau 2018-07-04 11:13:32 +02:00
parent f7ff31382b
commit 9a1d9fb1eb
1 changed files with 46 additions and 0 deletions
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@ -30,3 +30,49 @@ of dependencies and functionality that we do not need. At present we are using t
`init` process, and a small set of minimal scripts, but we expect to replace that with a small `init` process, and a small set of minimal scripts, but we expect to replace that with a small
standalone `init` process and a small piece of code to bring up the system containers where the standalone `init` process and a small piece of code to bring up the system containers where the
real work takes place. real work takes place.
## Console not displaying init or containerd output at boot
If you're not seeing `containerd` logs in the console during boot, make sure that your kernel `cmdline` configuration doesn't list multiple consoles.
`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.
## Troubleshooting containers
Linuxkit runs all services in a specific `containerd` namespace called `services.linuxkit`. To list all the defined containers:
```sh
(ns: getty) linuxkit-befde23bc535:~# ctr -n services.linuxkit container ls
CONTAINER IMAGE RUNTIME
getty - io.containerd.runtime.v1.linux
```
To list all running containers and their status:
```sh
(ns: getty) linuxkit-befde23bc535:~# ctr -n services.linuxkit task ls
TASK PID STATUS
getty 661 RUNNING
```
To list all processes running in a container:
```sh
(ns: getty) linuxkit-befde23bc535:/containers/services/getty# ctr -n services.linuxkit task ps getty
PID INFO
661 &ProcessDetails{ExecID:getty,}
677 -
685 -
686 -
687 -
1237 -
```
To attach a shell to a running container:
```sh
(ns: getty) linuxkit-befde23bc535:/containers/services/getty# ctr -n services.linuxkit tasks exec --tty --exec-id sh sshd /bin/ash -l
(ns: sshd) linuxkit-befde23bc535:/#
```
Containers are defined as OCI bundles in `/containers`.