How to check if there exists a process with a given pid in Python

Question

Is there a way to check to see if a pid corresponds to a valid process  I m getting a pid from a different source other than from os getpid   and I need to check to see if a process with that pid doesn t exist on the machine    I need it to be available in Unix and Windows  I m also checking to see if the PID is NOT in use

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I found that this solution seems to work well in both windows and linux  I used psutil to check  import psutil import subprocess import os p   subprocess Popen   python   self evaluation script  stdout subprocess PIPE  stderr subprocess STDOUT    pid   p pid  def   check process running   self p       if p is not None          poll   p poll           if poll    None              return True     return False      def   check PID running   self pid        quot  quot  quot          Checks if a pid is still running  UNIX works  windows we ll see          Inputs              pid - process id         returns              True if running  False if not      quot  quot  quot      if  platform system       Linux            try              os kill pid  0              if pid lt 0                  In case code terminates                 return False         except OSError              return False          else              return True     elif  platform system       Windows            return pid in  p pid for p in psutil process iter

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Combining Giampaolo Rodol   s answer for POSIX and mine for Windows I got this   import os if os name     posix       def pid exists pid              Check whether pid exists in the current process table             import errno         if pid  lt  0              return False         try              os kill pid  0          except OSError as e              return e errno    errno EPERM         else              return True else      def pid exists pid           import ctypes         kernel32   ctypes windll kernel32         SYNCHRONIZE   0x100000          process   kernel32 OpenProcess SYNCHRONIZE  0  pid          if process    0              kernel32 CloseHandle process              return True         else              return False

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The following code works on both Linux and Windows  and not depending on external modules import os import subprocess import platform import re  def pid alive pid int        quot  quot  quot  Check For whether a pid is alive  quot  quot  quot        system   platform uname   system     if re search  Linux   system  re IGNORECASE           try              os kill pid  0          except OSError              return False         else              return True     elif re search  Windows   system  re IGNORECASE           out   subprocess check output   quot tasklist quot   quot  fi quot  f quot PID eq  pid  quot    strip             b INFO  No tasks are running which match the specified criteria            if re search b No tasks   out  re IGNORECASE               return False         else              return True     else          raise RuntimeError f quot unsupported system  system  quot    It can be easily enhanced in case you need  other platforms other language

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mluebke code is not 100  correct  kill   can also raise EPERM  access denied  in which case that obviously means a process exists  This is supposed to work    edited as per Jason R  Coombs comments   import errno import os  def pid exists pid          Check whether pid exists in the current process table      UNIX only              if pid  lt  0          return False     if pid    0            According to  man 2 kill  PID 0 refers to every process           in the process group of the calling process            On certain systems 0 is a valid PID but we have no way           to know that in a portable fashion          raise ValueError  invalid PID 0       try          os kill pid  0      except OSError as err          if err errno    errno ESRCH                ESRCH    No such process             return False         elif err errno    errno EPERM                EPERM clearly means there s a process to deny access to             return True         else                According to  man 2 kill  possible error values are                EINVAL  EPERM  ESRCH              raise     else          return True   You can t do this on Windows unless you use pywin32  ctypes or a C extension module  If you re OK with depending from an external lib you can use psutil    gt  gt  gt  import psutil  gt  gt  gt  psutil pid exists 2353  True

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The answers involving sending  signal 0  to the process will work only if the process in question is owned by the user running the test  Otherwise you will get an OSError due to permissions  even if the pid exists in the system   In order to bypass this limitation you can check if  proc  lt pid gt  exists   import os  def is running pid       if os path isdir   proc     format pid            return True     return False   This applies to linux based systems only  obviously

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In Windows  you can do it in this way   import ctypes PROCESS QUERY INFROMATION   0x1000 def checkPid pid       processHandle   ctypes windll kernel32 OpenProcess PROCESS QUERY INFROMATION  0 pid      if processHandle    0          return False     else          ctypes windll kernel32 CloseHandle processHandle      return True   First of all  in this code you try to get a handle for process with pid given  If the handle is valid  then close the handle for process and return True  otherwise  you return False  Documentation for OpenProcess  https   msdn microsoft com en-us library windows desktop ms684320 28v vs 85 29 aspx

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In Python 3 3   you could use exception names instead of errno constants  Posix version   import os  def pid exists pid        if pid  lt  0  return False  NOTE  pid    0 returns True     try          os kill pid  0       except ProcessLookupError    errno ESRCH         return False   No such process     except PermissionError    errno EPERM         return True   Operation not permitted  i e   process exists      else          return True   no error  we can send a signal to the process

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This will work for Linux  for example if you want to check if banshee is running     banshee is a music player   import subprocess  def running process process        check if process is running   lt  process  gt  is the name of the process        proc   subprocess Popen   if pgrep     process      gt  dev null 2 gt  amp 1  then echo  True   else echo  False   fi    stdout subprocess PIPE  shell True        Process Existance  err    proc communicate       return Process Existance    use the function print running process  banshee

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Sending signal 0 to a pid will raise an OSError exception if the pid is not running  and do nothing otherwise   import os  def check pid pid                   Check For the existence of a unix pid          try          os kill pid  0      except OSError          return False     else          return True

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Building upon ntrrgc s I ve beefed up the windows version so it checks the process exit code and checks for permissions   def pid exists pid          Check whether pid exists in the current process table         if os name     posix           import errno         if pid  lt  0              return False         try              os kill pid  0          except OSError as e              return e errno    errno EPERM         else              return True     else          import ctypes         kernel32   ctypes windll kernel32         HANDLE   ctypes c void p         DWORD   ctypes c ulong         LPDWORD   ctypes POINTER DWORD          class ExitCodeProcess ctypes Structure                fields        hProcess   HANDLE                     lpExitCode   LPDWORD            SYNCHRONIZE   0x100000         process   kernel32 OpenProcess SYNCHRONIZE  0  pid          if not process              return False          ec   ExitCodeProcess           out   kernel32 GetExitCodeProcess process  ctypes byref ec           if not out              err   kernel32 GetLastError               if kernel32 GetLastError      5                    Access is denied                  logging warning  Access is denied to get pid info                kernel32 CloseHandle process              return False         elif bool ec lpExitCode                 print ec lpExitCode contents               There is an exist code  it quit             kernel32 CloseHandle process              return False           No exit code  it s running          kernel32 CloseHandle process          return True

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I d say use the PID for whatever purpose you re obtaining it and handle the errors gracefully  Otherwise  it s a classic race  the PID may be valid when you check it s valid  but go away an instant later

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Look here for windows-specific way of getting full list of running processes with their IDs   It would be something like  from win32com client import GetObject def get proclist        WMI   GetObject  winmgmts        processes   WMI InstancesOf  Win32 Process       return  process Properties   ProcessID   Value for process in processes    You can then verify pid you get against this list   I have no idea about performance cost  so you d better check this if you re going to do pid verification often   For  NIx  just use mluebke s solution

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Have a look at the psutil module       psutil  python system and process utilities  is a cross-platform library for retrieving information on running processes and system utilization  CPU  memory  disks  network  in Python        It currently supports Linux  Windows  OSX  FreeBSD and Sun Solaris  both 32-bit and 64-bit architectures  with Python versions from 2 6 to 3 4  users of Python 2 4 and 2 5 may use 2 1 3 version   PyPy is also known to work    It has a function called pid exists   that you can use to check whether a process with the given pid exists   Here s an example   import psutil pid   12345 if psutil pid exists pid       print  a process with pid  d exists    pid  else      print  a process with pid  d does not exist    pid    For reference    https   pypi python org pypi psutil https   github com giampaolo psutil http   pythonhosted org psutil  psutil pid exists

[python] How to check if there exists a process with a given pid in Python?

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