portpid — fast port-to-PID lookup by process name. Released under CC0 / Unlicense.

portpid

#!/usr/bin/env python3
import glob
import os
import sys


def hex_port(port: int) -> str:
    return f"{port:04X}"


def get_socket_inodes(target_port: int) -> set:
    port_hex = hex_port(target_port)
    inodes = set()
    for path in ("/proc/net/tcp", "/proc/net/tcp6"):
        try:
            with open(path) as f:
                next(f)  # skip header
                for line in f:
                    parts = line.split()
                    if len(parts) < 10:
                        continue
                    local = parts[1]
                    # local format: 0100007F:22B8 or 0000000000000000FFFF00000100007F:22B8
                    if ":" in local:
                        _, port_str = local.rsplit(":", 1)
                        if port_str.upper() == port_hex:
                            inodes.add(parts[9])
        except FileNotFoundError:
            pass
    return inodes


def pids_for_name(name: str):
    for comm_path in glob.glob("/proc/[0-9]*/comm"):
        try:
            with open(comm_path) as f:
                if f.read().strip() == name:
                    pid = comm_path.split("/")[2]
                    yield pid
        except (OSError, IOError):
            pass


def pid_has_socket_inode(pid: str, inodes: set) -> bool:
    fd_dir = f"/proc/{pid}/fd"
    try:
        for fd in os.listdir(fd_dir):
            try:
                link = os.readlink(os.path.join(fd_dir, fd))
                if link.startswith("socket:["):
                    inode = link[8:-1]
                    if inode in inodes:
                        return True
            except (OSError, IOError):
                pass
    except (OSError, IOError):
        pass
    return False


def main():
    if len(sys.argv) != 3:
        print(f"Usage: {sys.argv[0]} <procname> <port>", file=sys.stderr)
        sys.exit(2)

    procname = sys.argv[1]
    try:
        port = int(sys.argv[2])
    except ValueError:
        print("Port must be an integer", file=sys.stderr)
        sys.exit(2)

    inodes = get_socket_inodes(port)
    if not inodes:
        sys.exit(1)

    for pid in pids_for_name(procname):
        if pid_has_socket_inode(pid, inodes):
            print(pid)
            sys.exit(0)

    sys.exit(1)


if __name__ == "__main__":
    main()