Strange error during debugging program with threads: Unable open /proc file

Question

During debugging a program with threads, I have a strange error:

(gdb) info threads 
warning: unable to open /proc file '/proc/3663/status'
warning: Can't attach LWP 3663: No child processes
Cannot find new threads: debugger service failed

I get no other warnings during the debug session.

The process/thread 3663 doesn't exist.

How can it be that the gdb misunderstands the pid of the process/thread? What additional checks could I do to localize the problem?

score 0 · Accepted Answer · answered Jan 13 '14 at 10:38

0

I have found the reason of the failure.

The process I wanted to debug was in a process namespace; and the debugger was out of it. When I started the debugger in the same namespace the problem gone away.

answered Jan 13 '14 at 10:38

Igor Chubin

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What do you mean "process namespace"? – Wivlaro Aug 05 '14 at 21:51
Exactly, what do you mean by "process namespace"? I am hit with the same scenario, but not able to guess how you solved it. – Sandeep Aug 07 '14 at 07:32
@Wivlaro: If you don't know what that is, you probably do not need it at all. But if you really want it: http://www.haifux.org/lectures/299/netLec7.pdf – Igor Chubin Aug 08 '14 at 08:47
@Sandeep: See the previous comment – Igor Chubin Aug 08 '14 at 08:47
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@IgorChubin Can you elaborate on how you start the debugger in the same namespace? – Wivlaro Aug 09 '14 at 17:06
@Wivlaro: You must run tmux/screen in the namespace first, than start your process, and then open another terminal in screen and start the debugger in it – Igor Chubin Aug 11 '14 at 19:52

Strange error during debugging program with threads: Unable open /proc file

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