使用gcore进行核心转储，jmap转换为hprof文件格式失败，并显示错误消息 [英] Core dump taken with gcore, jmap conversion to hprof file format fails with Error message

问题描述

我们最近遇到了一个JVM崩溃，留下了gcore命令生成的核心转储文件。我们想看一下文件的内容，找出导致崩溃的确切原因。

We recently had one of our JVM's crash, leaving behind a core dump file produced by the gcore command. We want to have a look at the contents of the file and find out exactly what caused the crash.

使用 jmap 命令，您应该能够将核心转储文件转换为hprof文件格式的文件，然后您可以使用VisualVM和许多其他工具进行分析。我试过这个并收到错误信息。这是我运行的命令（在发生崩溃的同一个框中，使用相同的JVM）：

Using the jmap command you are supposed to be able to turn core dump files into files in the hprof file format, which you can then analyse using VisualVM and a number of other tools. I've tried this and get an error message. This was the command that I ran (on the same box that the crash took place, using the same JVM):

jmap -dump:format=b,file=dump.hprof /usr/java/jdk1.6.0_16/bin/java core.dump.2878

完整的回复是：

> Attaching to core core.dump.8483 from executable /usr/java/jdk1.6.0_16/bin/java, please wait...
> Error attaching to core file: Can't attach to the core file

这不是一个非常有用的错误消息。我想知道它是否是一个权限问题，但是我得到了运行该命令的相同消息，就像运行导致核心转储的JVM一样。我也想知道核心文件是否已损坏，所以我决定使用 gdb 来查看我是否可以打开核心文件并查看其中的内容。这就是我得到的：

That's not a very helpful error message. I wondered if it was a permissions issue, but I get the same message running the command as the same use that ran the JVM that caused the core dump. I also wondered if the core file was corrupt, so I decided to use gdb to see if I could open up the core file and see what was in it. This is what I get:

> gdb
GNU gdb (GDB) Red Hat Enterprise Linux (7.0.1-37.el5_7.1)
License GPLv3+: GNU GPL version 3 or later 
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
(gdb) core-file core.dump.8483
[New Thread 2889]
[New Thread 2893]
[New Thread 2894]
[New Thread 2895]
[New Thread 2896]
[New Thread 2904]
[New Thread 2915]
[New Thread 2916]
[New Thread 2917]
[New Thread 2921]
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[New Thread 3175]
[New Thread 3239]
[New Thread 3252]
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[New Thread 3356]
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[New Thread 4079]
[New Thread 4080]
[New Thread 6128]
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[New Thread 6497]
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[New Thread 10761]
[New Thread 10762]
[New Thread 11278]
[New Thread 11412]
[New Thread 11513]
[New Thread 11514]
[New Thread 2878]
(gdb) quit

此时我退出了，因为我完全不知道 gbd 以及如何使用它来诊断这类问题。我甚至不太明白最后一个命令是做什么的。值得注意的是，输出中确实存在134个新线程行，如果每个线代表JVM中产生的新线程，这可能是JVM死亡的原因。

And at that point I quit, because I know absolutely nothing about gbd and how to use it to diagnose this sort of issue. I don't even really understand what that last command did. One thing worth noting is that there are exactly 134 of those "New Thread" lines present in the output, and, if each one represents a new thread spawning in the JVM, this could be the reason the JVM died.

所以我的问题实际上是三折 -

So my question is in fact, three fold -

1）知道为什么 jmap 命令可能已经给出了该错误消息？

1) Any idea why the jmap command may have given that error message?

2）任何想法 gdb 输出是什么意思？

2) any ideas what the gdb output means?

3）是否知道如何使用 gdb 进一步诊断此问题？

3) any idea how to use gdb to further diagnose this issue?

推荐答案

顺便说一句，jvisualvm可以直接加载核心转储。但是你必须使用创建核心文件的相同jvm。

By the way, jvisualvm can load core dumps directly. But you must use the same jvm that created the core file.

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