Docker 中無法使用 JDK jmap之 Can't attach to the process: ptrace(PTRACE_ATTACH問題

問題描述

一個老服務最近出現OOM問題了（日誌中發現的），但是由於啓動參數沒有添加 -XX:+HeapDumpOnOutOfMemoryError無法獲取dump文件，這時想着使用jmap獲取dump文件，結果執行jmap報如下錯：

# jmap -heap 6
Attaching to process ID 6, please wait...
Error attaching to process: sun.jvm.hotspot.debugger.DebuggerException: Can't attach to the process: ptrace(PTRACE_ATTACH, ..) failed for 6: Operation not permitted
sun.jvm.hotspot.debugger.DebuggerException: sun.jvm.hotspot.debugger.DebuggerException: Can't attach to the process: ptrace(PTRACE_ATTACH, ..) failed for 6: Operation not permitted
	at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal$LinuxDebuggerLocalWorkerThread.execute(LinuxDebuggerLocal.java:163)
	at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal.attach(LinuxDebuggerLocal.java:278)
	at sun.jvm.hotspot.HotSpotAgent.attachDebugger(HotSpotAgent.java:671)
	at sun.jvm.hotspot.HotSpotAgent.setupDebuggerLinux(HotSpotAgent.java:611)
	at sun.jvm.hotspot.HotSpotAgent.setupDebugger(HotSpotAgent.java:337)
	at sun.jvm.hotspot.HotSpotAgent.go(HotSpotAgent.java:304)
	at sun.jvm.hotspot.HotSpotAgent.attach(HotSpotAgent.java:140)
	at sun.jvm.hotspot.tools.Tool.start(Tool.java:185)
	at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)
	at sun.jvm.hotspot.tools.HeapSummary.main(HeapSummary.java:49)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sun.tools.jmap.JMap.runTool(JMap.java:201)
	at sun.tools.jmap.JMap.main(JMap.java:130)
Caused by: sun.jvm.hotspot.debugger.DebuggerException: Can't attach to the process: ptrace(PTRACE_ATTACH, ..) failed for 6: Operation not permitted
	at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal.attach0(Native Method)
	at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal.access$100(LinuxDebuggerLocal.java:62)
	at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal$1AttachTask.doit(LinuxDebuggerLocal.java:269)
	at sun.jvm.hotspot.debugger.linux.LinuxDebuggerLocal$LinuxDebuggerLocalWorkerThread.run(LinuxDebuggerLocal.java:138)

問題分析

百度和google之後，我們發現docker的官方文檔提到了。

這不是什麼 docker 或者jmap的Bug，而是 Docker 自 1.10 版本開始加入的安全特性。類似於 jmap 這些 JDK 工具依賴於 Linux 的 PTRACE_ATTACH，而是 Docker 自 1.10 在默認的 seccomp 配置文件中禁用了 ptrace。

主要提及三種：

1.1 –security-opt seccomp=unconfined

直接關閉 seccomp 配置或者將ptrace添加到允許的名單中。用法：

docker run --security-opt seccomp:unconfined ...

官方文檔提到you can pass unconfined to run a container without the default seccomp profile. 連接爲https://docs.docker.com/engine/security/seccomp/

1.2 –cap-add=SYS_PTRACE

使用 --cap-add 明確添加指定功能：

docker run --cap-add=SYS_PTRACE ...

官方文檔連接https://docs.docker.com/engine/reference/run/

1.3 Docker Compose 的支持

Docker Compose 自 version 1.1.0 (2015-02-25) 起支持 cap_add。官方文檔：cap_add, cap_drop。用法：

前面的 docker-compose.yml 改寫後文件內容如下（相同內容部分就不重複貼了）：

version: '2'

services:
  mysql:
    ...
  api:
    ...
    cap_add:
      - SYS_PTRACE

官方連接在https://docs.docker.com/compose/compose-file/compose-file-v2/#cap_add-cap_drop

最終解決辦法

本人最終以類似如下方式啓動容器，然後 執行jmap命令

啓動容器的命令參數
docker run --cap-add=SYS_PTRACE -d -p 8080:8080 hello:v2  --name helloWithPtrace

# jmap -heap 6
Attaching to process ID 6, please wait...
Debugger attached successfully.
Server compiler detected.
JVM version is 25.162-b12

using thread-local object allocation.
Parallel GC with 2 thread(s)

Heap Configuration:
   MinHeapFreeRatio         = 0
   MaxHeapFreeRatio         = 100
   MaxHeapSize              = 782237696 (746.0MB)
   NewSize                  = 16777216 (16.0MB)
   MaxNewSize               = 260571136 (248.5MB)
   OldSize                  = 33554432 (32.0MB)
   NewRatio                 = 2
   SurvivorRatio            = 8
   MetaspaceSize            = 21807104 (20.796875MB)
   CompressedClassSpaceSize = 1073741824 (1024.0MB)
   MaxMetaspaceSize         = 17592186044415 MB
   G1HeapRegionSize         = 0 (0.0MB)

Heap Usage:
Exception in thread "main" java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at sun.tools.jmap.JMap.runTool(JMap.java:201)
	at sun.tools.jmap.JMap.main(JMap.java:130)
Caused by: java.lang.RuntimeException: unknown CollectedHeap type : class sun.jvm.hotspot.gc_interface.CollectedHeap
	at sun.jvm.hotspot.tools.HeapSummary.run(HeapSummary.java:144)
	at sun.jvm.hotspot.tools.Tool.startInternal(Tool.java:260)
	at sun.jvm.hotspot.tools.Tool.start(Tool.java:223)
	at sun.jvm.hotspot.tools.Tool.execute(Tool.java:118)
	at sun.jvm.hotspot.tools.HeapSummary.main(HeapSummary.java:49)
	... 6 more
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