When a program fails with bind: address already in use, Portop gives you an interactive way to see which process owns the port—and, when available, whether it belongs to a systemd service or Docker container. Luca Padovan describes it as: “See a port. Understand what’s behind it. Act on it.”
What Portop shows you
Portop is an open-source terminal UI written in Go. Its live table covers listening ports and established connections, connecting visible sockets to the process behind them and, where it can, to a service or container. The goal is to make port investigation more direct, rather than replace tools such as ss, lsof, Wireshark, or Docker’s own tooling.
Select a process and press Enter to inspect details including its command line, executable, working directory, user, memory use, thread count, and start time. The interface also supports searching and filtering, keyboard operation with mouse support, copying information, opening a local web service in a browser, and terminating a process.
How Portop connects sockets to processes
On Linux, Portop reads socket information from /proc/net/tcp, /proc/net/tcp6, /proc/net/udp, and /proc/net/udp6. It then maps socket inodes to processes by walking file descriptors under /proc/<pid>/fd. Systemd service and Docker container associations are derived primarily from cgroups.
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These associations provide context beyond a PID, but they depend on the information available on the system. Linux permissions also limit which processes a user can inspect; Padovan says running Portop with sudo provides additional visibility when needed.
Use Portop to investigate a busy port
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Start Portop with
portopand find the relevant listening port in the live table. You can start with a port or process-name filter to narrow the view. -
Select the process and press Enter to inspect its command, executable, working directory, user, and other process details.
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Use the available copy or browser-opening action to follow up, or terminate the process from the interface if that is the action you intend to take.
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Portop can identify the process behind a listener; deciding whether that process is safe to stop is still your responsibility. Check what it is and what depends on it before terminating it.
Check Docker Compose port mappings
For a Compose project, run portop --compose ./my-stack. Portop compares configured published ports with listeners and can surface expected mappings, conflicts, unused ports, and dynamic mappings. Container information can help show whether a listener belongs to the service you expected.
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This is useful when a configured service cannot bind, or when you want to compare the Compose configuration with what is actually listening. It does not make Docker tooling unnecessary when you need to manage or diagnose the container itself.
Use JSON, baselines, and watch mode
For scripts or repeatable checks, Portop provides JSON output and options to save or compare a listening-port baseline:
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portop --jsonoutputs JSON. -
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portop --diffcompares against a baseline and can return a nonzero exit code when it finds changes. -
portop --watch-newwatches for new listening ports.
For Compose JSON output, add --json to the Compose command: portop --compose ./my-stack --json. A nonzero status from --diff may indicate a detected change rather than a failure to run, so account for that behavior in scripts.
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Install Portop and check platform support
Padovan’s article lists these installation routes:
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Install with Go:
go install github.com/padovanl/portop/cmd/portop@latest. -
Use the shell installer or download a build from GitHub Releases.
The article lists Linux builds for amd64, arm64, armv7, and armv6, plus .deb and .rpm packages. It also describes macOS support for Intel and Apple Silicon. On macOS, Portop uses native lsof and ps rather than Linux’s /proc filesystem.
Release artifacts and installation instructions can change. Check the project’s current release page and repository instructions before choosing a package or running an installer. The article describes Portop as MIT-licensed and welcomes contributions.
When Portop is the right tool
Portop is a focused convenience layer when you want an interactive answer to “what owns this port?” plus process context, possible service or container attribution, Compose mapping checks, or JSON for automation. Use the underlying system, network, or Docker tools when you need their broader diagnostic or management capabilities.
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