子进程 pid 与 ps 输出不同
为什么子进程 pid (Popen.pid) 的值与 ps 命令返回的值不同？
当 ps 从 python 内部（使用 subprocess.call()）和另一个终端调用时，我注意到了这一点。
下面是一个要测试的简单 python 文件：
#!/usr/bin/python3
'''
Test subprocess termination
'''
import subprocess
command = 'cat'
#keep pipes so that cat doesn't complain
proc = subprocess.Popen(command,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
stdin=subprocess.PIPE,
shell=True)
print('pid = %d' % proc.pid)
subprocess.call("ps -A | grep -w %s" % command,
shell=True)
proc.terminate()
proc.wait() # make sure its dead before exiting pytyhon
通常 ps 报告的 pid 比 Popen.pid 报告的 pid 大 1 或 2。
Why is it that the subprocess pid (Popen.pid) has different value from that the ps command returns?
I've noticed this when ps called both from inside python (with subprocess.call()) and from another terminal.
Here's a simple python file to test:
#!/usr/bin/python3
'''
Test subprocess termination
'''
import subprocess
command = 'cat'
#keep pipes so that cat doesn't complain
proc = subprocess.Popen(command,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
stdin=subprocess.PIPE,
shell=True)
print('pid = %d' % proc.pid)
subprocess.call("ps -A | grep -w %s" % command,
shell=True)
proc.terminate()
proc.wait() # make sure its dead before exiting pytyhon
Usually the pid reported by ps is 1 or 2 more than that reported by Popen.pid.
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因为该命令是在
shell=True下运行的，所以 subprocess 返回的 pid 是用于运行该命令的 shell 进程的 pid。Because the command is run with
shell=True, the pid returned by subprocess is that of the shell process used to run the command.