lsof: List Open Files and Ports

How to use lsof to check open files, listening ports, and process file handles on Linux.

June 12, 2026

lsof: List Open Files and Ports

lsof is a command that lists all open files on the current system.

In Linux, everything — including network sockets, pipes, and devices — is treated as a file, so lsof can check not only regular files but also open ports and resources in use by processes.

1. Check All Open Files

Running it without any options lists all open files across the entire system.


List all open files
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2. Check Listening Ports

Use the -i option to filter network sockets.
Combining -P (show port numbers as numbers) and -n (skip hostname reverse lookup) speeds up the results.


Check all listening ports
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To find the process occupying a specific port, specify :port.


Check which process is using port 8080
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3. Check Open Files by Process

Use the -p option to list files opened by a specific PID.


Check open files by PID
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To search by process name, use the -c option.


Check open files by process name
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4. Check Open Files by User

Use the -u option to list all files opened by a specific user.


Check open files by user
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To exclude a specific user, prefix with ^.


Exclude root user from results
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5. Check Which Process Is Using a File

Check which process is using a specific file.
This is especially useful when a file cannot be deleted or umount fails.


Check which process is using a specific file
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The same approach works for finding processes occupying an entire mount point.


Check which process is using a mount point
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lsof is an essential command for a wide range of situations including debugging port conflicts, recovering deleted files, and tracking process resource usage.

Option Summary

Option	Description	Example
none	List all open files system-wide	`lsof`
`-i`	Filter network sockets	`lsof -i`
`-i :PORT`	Find process using a specific port	`lsof -i :8080`
`-P`	Show port numbers instead of service names	`lsof -i -P`
`-n`	Skip hostname reverse lookup (faster)	`lsof -i -n`
`-p PID`	List files opened by a specific PID	`lsof -p 1234`
`-c NAME`	Filter by process name	`lsof -c nginx`
`-u USER`	List files opened by a specific user	`lsof -u root`
`-u ^USER`	Exclude a specific user	`lsof -u ^root`

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