我tcpdump
在Python中运行,我想知道内核丢弃了多少数据包。
在命令行上运行时,tcpdump 如下所示:
me@mypc:$ sudo tcpdump -w myPackets.cap -i eth0 ip
tcpdump: listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes
^C28 packets captured
28 packets received by filter
0 packets dropped by kernel
这就是我tcpdump
在 Python 脚本中调用的方式:
f_out = open("tcpdumpSTDOUT", "w")
f_err = open("tcpdumpSTDERR", "w")
tcpdumpProcess = subprocess.Popen(['tcpdump',
'-w', 'myPackets.cap', '-i', 'eth0', '-n','ip'],
stdout=f_out,
stderr=f_err)
# a few seconds later:
tcpdumpProcess.kill()
f_in.close()
f_out.close()
现在,如果我看一下tcpdumpSTDERR
,我只会看到第一条通常的输出行:
tcpdump:监听 eth0,链路类型 EN10MB(以太网),捕获大小 65535 字节
其余的在哪里?
编辑 我尝试了一种不同的方法:
>>> myProcess = subprocess.Popen("tcpdump -w myPackets.cap -i eth2 ip", shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>> myProcess.communicate()
然后我从另一个 shell 中杀死了 tcpdump,并显示了 commnunicate() 的输出:
('', 'tcpdump: listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes\n')
...仍然只有第一行!
编辑 2 有趣的是:
>>> import shlex
>>> a = subprocess.Popen(shlex.split("tcpdump -w myPackets.cap -i eth2 ip"), stdout=subprocess.PIPE, stderr=subprocess.PIPE)
>>> a.terminate()
>>> a.communicate()
('', 'tcpdump: listening on eth2, link-type EN10MB (Ethernet), capture size 65535 bytes\n221 packets captured\n221 packets received by filter\n0 packets dropped by kernel\n')