Question

When a process is attached by gdb, the stat of the process is “T”, like:

root      6507  0.0  0.0  67896   952 ?        Ss   12:01   0:00 /mytest
root      6508  0.0  0.0 156472  7120 ?        Sl   12:01   0:00 /mytest
root     26994  0.0  0.0  67896   956 ?        Ss   19:59   0:00 /mytest
root     26995  0.0  0.0 156460  7116 ?        Tl   19:59   0:00 /mytest
root     27833  0.0  0.0  97972 24564 pts/2    S+   20:00   0:00 gdb /mytest

From the above, 26995 may be debuging. How can I know 26995 is debug or not? Or can I know which process is attached by gdb(27833)

pstree -p 27833 — show gdb(27833)

Another question: How to know a process(stat: T) is attached by which gdb(PID)?
In most siduation, I am not the peoson who is debuging the process.

Answer 1

The T in ps output stands for “being ptrace()d”. So that process (26995) is being traced by something. That something is most often either GDB, or strace.

So yes, if you know that you are only running GDB and not strace, and if you see a single process in T state, then you know that you are debugging that process.

You could also ask GDB which process(es) it is debugging:

(gdb) info process
(gdb) info inferior

Update
As Matthew Slattery correctly noted, T just means the process is stopped, and not that it is being ptrace()d.

So a better solution is to do this:

 grep '^TracerPid:' /proc/*/status | grep -v ':.0'
 /proc/7657/status:TracerPid:    31069

From above output you can tell that process 7657 is being traced by process 31069. This answers both “which process is being debugger” and “which debugger is debugging what”.