Why can't gdb attach to server application summoned with inetd?

Question

I have a server application that can be summoned for the client using inetd. However, if I try to attach to the server process that was launched with inetd, I get the following response: ptrace: Operation not permitted.

gdb --annotate=3 /my/app/here <processId>

Current directory is /usr/local/bin/
GNU gdb 6.8
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License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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This GDB was configured as "i686-pc-linux-gnu"...
Reading symbols from /usr/local/bin/flumed...done.
Using host libthread_db library "/lib/tls/libthread_db.so.1".
Attaching to program: /my/app/here, process <processId>
ptrace: Operation not permitted.
/usr/local/bin/<processId>: No such file or directory.
(gdb) 

Answer 1

Apparently, things get funky with inetd where the userid is not root. You end up with a process with weird permissions. For example, you are unable to read /proc/self/exe even though the permissions are 777. I suspect this issue is more of the same. Even though I'm the userid of the process, I don't have permissions. Using root for gdb is a work around.

Answer 2

I have also seen this problem occur when multiple instances of gdb are running at the same time, usually because I failed to close gdb correctly. Closing these leaked instances fixed the problem.

Answer 3

Pls run the following command to solve ur problem:

sudo chmod +s /usr/bin/gdb

Answer 4

Solution for me was this:

echo 0 | sudo tee /proc/sys/kernel/yama/ptrace_scope

Answer 5

Further to what tgoodhart said, other ptrace users like /usr/bin/strace will also block gdb.