Identifying listening ports using Python

In translating some scripts from bash, I am encountering many uses of netstat -an to find if one of our services is listening. While I know I can just use subprocess.call or other even popen I would rather use a pythonic solution so I am not leveraging the unix environment we are operating in.

From what I have read the socket module should have something but I haven't seen anything that checks for listening ports. It could be me not understanding a simple trick, but so far I know how to connect to a socket, and write something that lets me know when that connection failed. But not necessarily have I found something that specifically checks the port to see if its listening.

Any ideas?

sberry

How about trying to connect...

import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
result = s.connect_ex(('127.0.0.1', 3306))

if result == 0:
    print('socket is open')
s.close()

I know this question is old, but i write this for begginners. If you want identifying listening ports on your system, you can use the code below.

from socket import *

Port = 0 #First port.
while Port <= 65535: #Port 65535 is last port you can access.
    try:
        try:
            Socket = socket(AF_INET, SOCK_STREAM, 0) #Create a socket.
        except:
            print("Error: Can't open socket!\n")    
            break #If can't open socket, exit the loop.
        Socket.connect(("127.0.0.1", Port)) #Try connect the port. If port is not listening, throws ConnectionRefusedError. 
        Connected = True
    except ConnectionRefusedError:
        Connected = False       
    finally:
        if(Connected and Port != Socket.getsockname()[1]): #If connected,
            print("{}:{} Open \n".format("127.0.0.1", Port)) #print port.
        Port = Port + 1 #Increase port.
        Socket.close() #Close socket.

You could either try connecting to the port in question, or emulate netstat.

Doing the latter will be OS-specific. On Linux you can examine /proc/net/tcp. It looks like this:

  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode                                                     
   0: 00000000:C809 00000000:0000 0A 00000000:00000000 00:00000000 00000000   117        0 8381 1 ffff8802f22a8000 300 0 0 2 -1                      
   1: 00000000:16CC 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1026        0 14336 1 ffff8802f2249440 300 0 0 2 -1                     
   2: 00000000:006F 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 7876 1 ffff8802f2248000 300 0 0 2 -1                      
   3: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 8163 1 ffff8802f3578000 300 0 0 2 -1                      
   4: 0100007F:0277 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 981582 1 ffff8800d7a53600 300 0 0 2 -1                    
   5: 00000000:0019 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 9129 1 ffff8802edc886c0 300 0 0 2 -1                      
   6: 00000000:021A 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 9016 1 ffff8802edc88000 300 0 0 2 -1                      
   7: 00000000:2B1C 00000000:0000 0A 00000000:00000000 00:00000000 00000000  1026        0 783709 1 ffff8803119cca40 300 0 0 2 -1                    
   8: 00000000:977C 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 24292 1 ffff8802f224e540 300 0 0 2 -1

You're looking for lines that have 0A in the st ("status") column. The numbers after the colon in local_address -- C809, 16CC etc -- are TCP port numbers (in hex) on which there are listening processes.

richardw

On Linux we can use strace to see that netstat -ln is reading and parsing various values from the /proc filesystem.

$ strace netstat -ln 2>&1| grep '/proc'
open("/proc/net/tcp", O_RDONLY)         = 3
open("/proc/net/tcp6", O_RDONLY)        = 3
open("/proc/net/udp", O_RDONLY)         = 3
open("/proc/net/udp6", O_RDONLY)        = 3
open("/proc/net/raw", O_RDONLY)         = 3
open("/proc/net/raw6", O_RDONLY)        = 3
open("/proc/net/unix", O_RDONLY)        = 3
open("/proc/net/ipx/socket", O_RDONLY)  = -1 ENOENT (No such file or directory)
open("/proc/net/ipx", O_RDONLY)         = -1 ENOENT (No such file or directory)
open("/proc/net/ax25", O_RDONLY)        = -1 ENOENT (No such file or directory)
open("/proc/net/x25", O_RDONLY)         = -1 ENOENT (No such file or directory)
open("/proc/net/x25", O_RDONLY)         = -1 ENOENT (No such file or directory)
open("/proc/net/nr", O_RDONLY)          = -1 ENOENT (No such file or directory)

So you can just read those files from Python and extract the data you need.

$ cat /proc/net/tcp
  sl  local_address rem_address   st tx_queue rx_queue tr tm->when retrnsmt   uid  timeout inode
   0: 00000000:0050 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 8190 1 00000000 300 0 0 2 -1
   1: 00000000:0016 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 6458 1 00000000 300 0 0 2 -1
   2: 0100007F:0277 00000000:0000 0A 00000000:00000000 00:00000000 00000000     0        0 10425 1 00000000 300 0 0 2 -1
   3: 8D0BA8C0:8801 689255D1:01BB 01 00000000:00000000 00:00000000 00000000  1000        0 1680975 1 00000000 24 4 16 6 -1
   4: 8D0BA8C0:D142 97E67D4A:01BB 06 00000000:00000000 03:000012E8 00000000     0        0 0 3 00000000
   5: 8D0BA8C0:D1A1 96E67D4A:01BB 01 00000000:00000000 00:00000000 00000000  1000        0 1672130 1 00000000 24 4 18 5 -1
   6: 8D0BA8C0:D148 97E67D4A:01BB 01 00000000:00000000 00:00000000 00000000  1000        0 1679875 1 00000000 24 4 20 5 -1

The listening sockets will have remote address 00000000:0000

The address:port pairs are in hex. See: * How can i match each /proc/net/tcp entry to each opened socket?

You could cross reference with /proc//fd. For example, sshd is running on my laptop.

$ cat /var/run/sshd.pid
522

$ sudo ls -l /proc/522/fd
total 0
lrwx------ 1 root root 64 2011-09-15 21:32 0 -> /dev/null
lrwx------ 1 root root 64 2011-09-15 21:32 1 -> /dev/null
lrwx------ 1 root root 64 2011-09-15 21:32 2 -> /dev/null
lrwx------ 1 root root 64 2011-09-15 21:32 3 -> socket:[6456]
lrwx------ 1 root root 64 2011-09-15 21:32 4 -> socket:[6458]

Socket 6456 corresponds to inode 6458 listed in the second row of /proc/net/tcp.

So you can get all this information from proc, but you may end up reinventing netstat -lntp

来源：https://stackoverflow.com/questions/7436801/identifying-listening-ports-using-python

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