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What Are Listeners?

Listeners are processes on your system that expose network ports, accepting incoming connections. When you run a web server, database, or any service that listens on a port, psys detects and displays it in the listeners table. psys uses the Linux ss (socket statistics) command to discover all listening TCP sockets on your system: 
ss -tlnp

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Listeners Table Columns

The listeners table displays comprehensive information about each listening process:

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Process

Shows the process name with an appropriate icon. psys automatically detects common services and displays recognizable icons for:
  • Node.js processes
  • Next.js applications
  • Redis servers
  • MongoDB databases
  • PostgreSQL databases
  • MySQL/MariaDB databases
  • Apache/httpd web servers
  • SSH daemons
If the process is the psys app itself, it shows a special psys icon.

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Docker Status

Indicates whether this port is published by a Docker container. When Docker publishes a container port to the host, psys shows the Docker icon and uses the container name as the service label.

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Port

The TCP port number the process is listening on.

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Address

The IP address the service is bound to. Common addresses include:
  • 0.0.0.0 - Listening on all IPv4 interfaces
  • 127.0.0.1 - Localhost only (IPv4)
  • ::, ::1, [::1] - IPv6 addresses
  • Private network addresses (10.x, 192.168.x, 172.x)

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Address Description

psys provides human-readable explanations of what each address means: 
function getAddressDescription(addr: string): string {
  const a = addr.trim();
  if (a === "0.0.0.0") return "Listening on all IPv4 interfaces";
  if (a === "127.0.0.1") return "Localhost only (IPv4)";
  if (a === "[::1]" || a === "::1" || a === "::") return "Localhost or all IPv6";
  if (a === "127.0.0.53") return "systemd-resolved (local DNS)";
  if (a === "127.0.0.54") return "Local DNS (alternative)";
  if (a.startsWith("127.") || a.startsWith("10.") || a.startsWith("192.168.") || a.startsWith("172.")) 
    return "Local network (IPv4)";
  if (a.startsWith("[") && a.includes("]")) return "IPv6 address";
  return "Other interface";
}
The address 127.0.0.53 is typically used by systemd-resolved, the system DNS resolver on modern Linux distributions.

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Connections

Displays badge indicators for established connections from this listener to other services. Shows up to 5 connection targets with a “+N” badge if there are more.

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PID

The Process ID of the listening process. This is used for process management operations.

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Service Label Detection

psys automatically recognizes common services by their port numbers and provides helpful labels: 
function knownListenerService(port: number): string | undefined {
  const known: Record<number, string> = {
    22: "SSH",
    53: "DNS (systemd-resolved)",
    80: "Apache / HTTP",
    443: "HTTPS",
    3000: "Node/Express",
    3001: "Node/Express",
    3002: "psys (this app)",
    631: "CUPS (printing)",
    6379: "Redis",
    27017: "MongoDB",
    5432: "PostgreSQL",
    3306: "MySQL",
    5672: "RabbitMQ",
    9200: "Elasticsearch",
  };
  return known[port];
}
When a process cannot be identified (shown as ”?”), psys uses the known port mapping to suggest what service might be running. For example, port 6379 will be labeled as “6379 (typical: Redis)”.
psys prioritizes showing Docker container names when a port is published by Docker, then falls back to the known service detection.

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How Detection Works

The detection logic follows this priority:
  1. psys itself - Identifies if the listener is the psys app
  2. Docker containers - Uses docker ps to match ports to container names
  3. Process name - Reads from /proc/{pid}/comm
  4. Known ports - Falls back to well-known port mappings
  5. Unknown - Shows “port (unknown)” if nothing matches
This multi-layered approach ensures you always have meaningful information about what’s listening on your system.