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<main>
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<h1 id="debugging"><a class="header" href="#debugging">Debugging</a></h1>
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<p>Since Youki uses pipe and double-fork in the creating phase, it is hard to debug what happened.
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You might encounter the error message, "Broken pipe ..." Unfortunately,
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this error message has only information that a child process exists with an error for some reason.</p>
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<p>This section will give some tips to debug youki to know what happens in the child processes.</p>
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<h1 id="bpftrace"><a class="header" href="#bpftrace">bpftrace</a></h1>
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<p><a href="https://github.com/iovisor/bpftrace">bpftrace</a> is an eBPF based tool.
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In the case of youki, you can catch the system calls youki issued.</p>
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<p>For example, if you catch write system calls, you can see the log output until the middle of process.
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It allows you to do something similar to print debugging.</p>
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<p><em>How to debug</em></p>
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<ol>
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<li>
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<p>You need to install bpftrace, please refer to <a href="https://github.com/iovisor/bpftrace/blob/master/INSTALL.md">the official documentation</a> to know how to install it.</p>
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</li>
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<li>
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<p>Before running the process or comannd you want to debug, run the following command in another terminal.</p>
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<p>You need the root privilege to run it.</p>
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<pre><code class="language-console">$ cd ${youki_repo}
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$ just hack-bpftrace
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</code></pre>
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</li>
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<li>
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<p>Run the command you want to debug.</p>
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</li>
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</ol>
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<p><em>For example</em></p>
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<ol>
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<li>
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<p>Run the bpftrace script.</p>
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<pre><code class="language-console">$ just hack-bpftrace
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BPFTRACE_STRLEN=120 ./hack/debug.bt
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Attaching 13 probes...
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Tracing Youki syscalls... Hit Ctrl-C to end.
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TIME COMMAND PID EVENT CONTENT
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</code></pre>
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</li>
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<li>
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<p>Run the Kubernetes cluster using kind with youki</p>
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<pre><code class="language-console">$ cd ${youki_repo}
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$ just test-kind
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docker buildx build --output=bin/ -f tests/k8s/Dockerfile --target kind-bin .
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...
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Creating cluster "youki" ...
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...
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kubectl --context=kind-youki apply -f tests/k8s/deploy.yaml
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runtimeclass.node.k8s.io/youki created
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deployment.apps/nginx-deployment created
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...
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kubectl --context=kind-youki delete -f tests/k8s/deploy.yaml
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runtimeclass.node.k8s.io "youki" deleted
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deployment.apps "nginx-deployment" deleted
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</code></pre>
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</li>
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<li>
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<p>Returning to the first command executed, the system calls youki issued are caught and logged.</p>
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<pre><code class="language-console">$ just hack-bpftrace
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BPFTRACE_STRLEN=120 ./hack/debug.bt
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Attaching 13 probes...
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Tracing Youki syscalls... Hit Ctrl-C to end.
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TIME COMMAND PID EVENT CONTENT
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207033348942 youki 13743 open errno=2, fd=-1, file=/opt/containerd/lib/glibc-hwcaps/x86-64-v3/libc.so.6
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...
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207035462044 youki 13743 open errno=0, fd=3, file=/proc/self/exe
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207035478523 youki 13743 write fd=4, ELF
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207066996623 4 13743 open errno=2, fd=-1, file=/opt/containerd/lib/glibc-hwcaps/x86-64-v3/libc.so.6
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...
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207070130175 4 13743 clone3
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207070418829 youki:[1:INTER] 13747 write fd=4, {"timestamp":"2023-09-24T10:47:07.427846Z","level":"INFO","message":"cgroup manager V2 will be used","target":"libcgrou
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...
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207084948440 youki:[1:INTER] 13747 clone3
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207085058811 youki:[1:INTER] 13747 write fd=4, {"timestamp":"2023-09-24T10:47:07.442502Z","level":"DEBUG","message":"sending init pid (Pid(1305))","target":"libcontai
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207085343170 youki:[2:INIT] 13750 write fd=4, {"timestamp":"2023-09-24T10:47:07.442746Z","level":"DEBUG","message":"unshare or setns: LinuxNamespace { typ: Uts, path
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...
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207088256843 youki:[2:INIT] 13750 pivt_root new_root=/run/containerd/io.containerd.runtime.v2.task/k8s.io/0fea8cf5f8d1619a35ca67fd6fa73d8d7c8fc70ac2ed43ee2ac2f8610bb938f6/r, put_old=/run/containerd/io.containerd.runtime.v2.task/k8s.io/0fea8cf5f8d1619a35ca67fd6fa73d8d7c8fc70ac2ed43ee2ac2f8610bb938f6/r
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...
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207097207551 youki:[2:INIT] 13750 write fd=4, {"timestamp":"2023-09-24T10:47:07.454645Z","level":"DEBUG","message":"found executable in executor","executable":"\"/pa
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...
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207139391811 youki:[2:INIT] 13750 write fd=4, {"timestamp":"2023-09-24T10:47:07.496815Z","level":"DEBUG","message":"received: start container","target":"libcontainer
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207139423243 youki:[2:INIT] 13750 write fd=4, {"timestamp":"2023-09-24T10:47:07.496868Z","level":"DEBUG","message":"executing workload with default handler","target"
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</code></pre>
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