容器被无法获取java进程调试
今天尝试在容器内使用arthas调试，发现无法attch到java进程，jstack命令也无法获取到java进程
问题描述
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使用arthas提示错误
Unable to get pid of LinuxThreads manager thread
相关问题连接
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jmap not happy on alpine · Issue #76 · docker-library/openjdk · GitHub
结论：
If you keep bash as PID 1, you'd no longer get signals from
docker stopanddocker kill(without having to write traps). With docker 1.13 you can use--initto have docker put in tini as PID 1; it'll forward signals and reap zombies.（自行翻译）
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结论：
使用alpine方式打包镜像【FROM openjdk:8-jdk-alpine】，会出现这种情况。通过使用tini插件，可以解决。
解决方法
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修改
Dockerfile添加tini（添加
RUN apk add --no-cache tini，并且在ENTRYPOINT添加tini）：FROM openjdk:8-jre-alpine ... # Install Tini RUN apk add --no-cache tini ENTRYPOINT ["/sbin/tini", "--", "sh", "entrypoint.sh"]
问题分析
because PID 1 is special and it doesn’t handle any signal unless explicitly declared. So the workaround is to have the java process spawned at non PID 1.
因为启动java的进程ID为1，而PID1是特殊的进程号，不处理任何信号，除非显示声明。所以，我们的解决方案就是：让java进程的ID不为1。而tini就是这个作用：*All Tini does is spawn a single child (Tini is meant to be run in a container), and wait for it to exit. All the while reaping zombies and performing signal forwarding.*
Tini所做的就是生成一个子节点(Tini是在容器中运行的)，然后等待它退出。进行信号转发。
结论
学习了新的技能。
