💡 Performance & Debugging March 1, 2026 6

Linux Command: lsof

List open files and the processes that opened them

Terminal — Performance & Debugging

Command

$ sudo lsof -i :80

Output

Shows which process is listening on port 80.

lsof (list open files) shows all files opened by processes. In Linux, everything is a file — network sockets, pipes, devices, and regular files — so lsof provides a comprehensive view of system activity. lsof is essential for finding which process is using a port, which processes have a file open (preventing unmount), and diagnosing resource leaks. It is one of the most versatile troubleshooting tools. lsof can filter by user, process, file, network port, and more. It shows the process name, PID, user, file descriptor, type, and file/socket details.

Syntax

lsof [OPTION]...

Common Examples

sudo lsof -i :80 — Shows which process is listening on port 80.
sudo lsof -i -P -n — Shows all network connections without DNS resolution.
lsof -p $(pgrep nginx | head -1) — Shows all files opened by the nginx process.
lsof /var/log/syslog — Shows processes that have syslog open.