서버를 만들고, 여러 테스트하는 것 중에 영구 접속이 끊어지는 상황을 재현하는 것은 쉽지 않을 수 있다. 디버거를 이용하여 간단히 종료시켜 보는 법을 알아 본다.
python으로 돌고 있는 데몬(pid 11688)이 있다고 하고, 데몬의 DB 접속은 영구 접속에 해당하는데, 이 접속을 강제로 종료시키는 것을 가정한다.
$ lsof -n -p 11688
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
python 11688 pynoos cwd DIR 202,3 80 1636949 /misc/django_projects/app/broadcast
python 11688 pynoos rtd DIR 202,3 4096 128 /
python 11688 pynoos txt REG 202,3 7216 53035 /usr/bin/python
python 11688 pynoos mem REG 202,3 12408 134524267 /usr/lib64/python/lib-dynload/grpmodule.so
python 11688 pynoos mem REG 202,3 13520 134538649 /usr/lib64/python/lib-dynload/_bisectmodule.so
python 11688 pynoos mem REG 202,3 48240 134524376 /usr/lib64/python/lib-dynload/arraymodule.so
python 11688 pynoos mem REG 202,3 694224 134524317 /usr/lib64/python/lib-dynload/unicodedata.so
python 11688 pynoos mem REG 202,3 24176 134524160 /usr/lib64/python/lib-dynload/zlibmodule.so
python 11688 pynoos mem REG 202,3 14496 69180222 /usr/lib64/libutil-2.17.so
...
... (생략)
...
python 11688 pynoos mem REG 202,3 19288 69048848 /usr/lib64/libdl-2.17.so
python 11688 pynoos mem REG 202,3 142232 69048881 /usr/lib64/libpthread-2.17.so
python 11688 pynoos mem REG 202,3 1847496 67226793 /usr/lib64/libpython.so.1.0
python 11688 pynoos mem REG 202,3 163400 69048840 /usr/lib64/ld-2.17.so
python 11688 pynoos 0r CHR 1,3 0t0 1028 /dev/null
python 11688 pynoos 1u CHR 136,4 0t0 7 /dev/pts/4
python 11688 pynoos 2u CHR 136,4 0t0 7 /dev/pts/4
python 11688 pynoos 3w REG 202,3 3009102 136203946 /misc/log/projects/app.log
python 11688 pynoos 4r CHR 1,9 0t0 1033 /dev/urandom
python 11688 pynoos 5w REG 202,3 266251952 135014754 /misc/log/projects/app.sql
python 11688 pynoos 6u IPv4 26138940 0t0 UDP *:9413
python 11688 pynoos 7u IPv4 26137372 0t0 TCP 10.1.1.1:33148->10.1.1.2:mysql (ESTABLISHED)먼저 열려 있는 파일들의 리스트(list of open files; lsof)를 확인한다. 위의 예에서는 7u로 되어 있는 값이 mysql 커넥션 디스크립터다. 이 디스크립터를 종료하면 mysql과의 접속이 종료되는 것이다.
$ gdb /usr/bin/python 11688
GNU gdb (GDB) Red Hat Enterprise Linux 7.6.1-115.el7
Copyright (C) 2013 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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/>...
Reading symbols from /usr/bin/python...Reading symbols from /usr/bin/python...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Attaching to program: /usr/bin/python, process 11688
Reading symbols from /lib64/libpython.so.1.0...Reading symbols from /lib64/libpython.so.1.0...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /lib64/libpython.so.1.0
Reading symbols from /lib64/libpthread.so.0...(no debugging symbols found)...done.
[New LWP 12995]
[New LWP 12994]
[New LWP 12992]
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Loaded symbols for /lib64/libpthread.so.0
Reading symbols from /lib64/libdl.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib64/libdl.so.2
...
... (생략)
...
Loaded symbols for /usr/lib64/python/lib-dynload/arraymodule.so
Reading symbols from /usr/lib64/python/lib-dynload/_bisectmodule.so...Reading symbols from /usr/lib64/python/lib-dynload/_bisectmodule.so...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/python/lib-dynload/_bisectmodule.so
Reading symbols from /usr/lib64/python/lib-dynload/grpmodule.so...Reading symbols from /usr/lib64/python/lib-dynload/grpmodule.so...(no debugging symbols found)...done.
(no debugging symbols found)...done.
Loaded symbols for /usr/lib64/python/lib-dynload/grpmodule.so
0x00007f0de576b953 in select () from /lib64/libc.so.6
(gdb) call close(7)
$1 = 0gdb는 디버깅 중인 프로세스의 입장으로 간단한 시스템 콜을 호출 할 수 있는데, 마지막 명령처럼 "call close(7)" 을 호출하면, 디스크립터를 종료하게 된다. 그리고, ^D를 눌러 gdb를 종료하면 프로세스는 실행을 재개하며, 영문도 모르는 채 DB 접속이 끊어지는 상황을 만나게 된다.
Happy Debugging.
