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lsoff identifies processes associated with listening TCP ports and bound UDP ports on Windows, Linux, and macOS. It can filter results by port or process details and display them in a terminal interface, a table, or JSON. Use it to investigate a port, but treat missing process details as a permissions issue to check—not proof that no process owns the socket.
What lsoff shows
The lsoff project describes the program as a port-focused CLI/TUI for listing processes associated with listening TCP and UDP ports. Search terms can include a port, process name, PID, command line, path, project, or service. Its README documents an interactive TUI, tabular output when standard output is not a terminal, and JSON output. These are project-documented capabilities; they have not been independently tested for this article. lsoff project README
UDP needs a careful interpretation: unlike TCP, it does not have a LISTEN state. lsoff reports UDP sockets bound to a port that have no remote peer; calling these “listening” in the TCP-state sense would be misleading.
Install lsoff on your operating system
The project documents support for Windows, Linux, and macOS, with installation through release binaries, package managers, Go, or a source build. macOS builds require CGO because lsoff uses libproc. Follow the project’s current README for platform-specific instructions and available release targets. lsoff project README
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- Windows: the README lists WinGet:
winget install yutat23.lsoff. - macOS: the documented Homebrew route is
brew tap yutat23/tap, followed bybrew install lsoff. The README notes a third-party tap trust step for Homebrew 6. - Go: install the latest tagged project version using
go install github.com/yutat23/lsoff@latest. - Any supported target: download a release binary or build from source using the project instructions.
The commands above are installation examples documented by the project, not commands independently verified here. The README also says the version is baked into the binary at build time, so after an update or rebuild, check that lsoff -v corresponds to the source version you expect.
Find and inspect a port
Run a port query in a terminal, or use a filter to narrow the results. These example invocations come from the lsoff README:
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- Supported features include Wake-on-LAN function, Green Ethernet & IEEE 802.3az-2010 (Energy Efficient Ethernet)
- Supports IPv4/IPv6 pack Checksum Offload Engine (COE) to reduce Cental Processing Unit (CPU) loading
- Compatible with Windows 8.1 or higher, Mac OS
lsoff 8080— search for port 8080.lsoff -u 53— search UDP port 53.lsoff --json nginx— request JSON output while searching for nginx.
When reviewing a match, use the process name and PID to identify the owner, then inspect the command line or path when available to distinguish the intended service from an unrelated program. If the output is incomplete, first consider whether your account can inspect the process; the project warns that PID, executable path, and command-line fields may be empty without sufficient permission. Its README suggests running as root on Unix-like systems or as Administrator on Windows when those details are required. lsoff project README
Use process termination cautiously
lsoff documents a -k option to terminate matching processes. Its examples include lsoff -k 8080 and lsoff -k -y 8080; the -y option skips confirmation and is required when output is piped. Terminating a process can interrupt an application or service, so identify the process and understand its role before proceeding. Avoid confirmation bypass unless the command and its target are deliberate.
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The project documents a remaining PID-reuse race on macOS: it rechecks before calling kill(2), but macOS lacks a pidfd-equivalent protection for the final interval before termination. This is a project-stated implementation limitation, not a guarantee that every termination attempt will affect the intended process. lsoff project README
How lsoff gathers process information—and where it can fall short
According to the project README, lsoff collects Linux socket data from /proc/net/{tcp,tcp6,udp,udp6} and process details from /proc/<pid>/{fd,cmdline,cwd}. On macOS, it uses libproc and sysctl kern.procargs2. On Windows, it uses IP Helper and process-information APIs. The project says it does not shell out to lsof, ss, or netstat. These are implementation details reported by the project and have not been independently tested here. lsoff project README
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Two Windows caveats are documented. Command-line and current-working-directory collection uses NtQueryInformationProcess, an internal Microsoft API that may change. The README also describes a 32-bit inspection limitation for command-line and working-directory details of 64-bit processes. Permission restrictions can also leave process fields empty on any supported platform, so incomplete attribution should not be treated as a definitive absence of a process.
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When lsof may be a better fit
On Unix-like systems, lsof -i lists Internet socket files and can be narrowed by protocol and port. That broader open-file inspection may suit users who want to investigate more than ports; lsoff is oriented around port searches and documents Windows support as well as Linux and macOS. The projects document different scopes, so these descriptions do not establish exact feature parity. For lsof’s socket options, see its documentation.
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