Master the Linux ‘lsof’ Command: A Comprehensive Guide for Beginners

This article provided a comprehensive guide on the Linux ‘lsof’ command, covering its history, use cases, usage, parameters, and effective techniques. Through various examples, newcomers to Linux can gain an understanding and effectively use the ‘lsof’ command.

Instructions

This guide aims to provide a comprehensive understanding of the ‘lsof’ command in Linux. It covers the history, usage, and applications of ‘lsof’. Additionally, it discusses commonly used and additional supported parameters and provides a number of common use cases and effective techniques for using the ‘lsof’ command.

History

The ‘lsof’ command has been a part of Unix/Linux systems for many years. It’s an invaluable tool for developers and system administrators who need to investigate system resources.

When and why to use it

When you need to list open files handled by the system processes, the ‘lsof’ command is useful. It provides extensive information on all files that are opened by processes.

How to use it

The ‘lsof’ command can be run without any options, which will list all the open files handled by all active processes.

$ lsof
COMMAND     PID   TID USER   FD      TYPE             DEVICE SIZE/OFF       NODE NAME
systemd       1         root  cwd       DIR                8,1     4096          2 /
systemd       1         root  rtd       DIR                8,1     4096          2 /

The commonly used parameters

• u List files owned by user(s).

$ lsof -u root
COMMAND     PID USER   FD      TYPE             DEVICE SIZE/OFF       NODE NAME
systemd       1 root  cwd       DIR                8,1     4096          2 /
systemd       1 root  rtd       DIR                8,1     4096          2 /

• c List files for specific command.

$ lsof -c systemd
COMMAND     PID   TID USER   FD      TYPE             DEVICE SIZE/OFF       NODE NAME
systemd       1         root  cwd       DIR                8,1     4096          2 /
systemd       1         root  rtd       DIR                8,1     4096          2 /

Other supported parameters

• -a : AND selections
• -b : Avoid kernel blocks.
• -d : File descriptor selection.
• -D : Directory selection.
• -f : File structure selection.
• -g : Process group selection.
• -i : Select IPv[46], TCP or UDP files.
• -l : List UID numbers.
• -n : Avoid network names.
• -P : Avoid port names.
• -r : Repeat listing.
• -s : File size selection.
• -S : Interrupt display.

Most common use cases

One of the most common uses of ‘lsof’ is to determine which process is using a specific file or directory.

$ lsof /path/to/directory
COMMAND     PID   TID USER   FD      TYPE             DEVICE SIZE/OFF       NODE NAME
process      123       user  cwd       DIR                8,1     4096          2 /path/to/directory

The tricky skills

You can use ‘lsof’ with other commands to achieve more specific information. For instance, you can use ‘lsof’ with ‘grep’ to find specific processes that are using a certain file or directory.

$ lsof | grep "/path/to/directory"
COMMAND     PID   TID USER   FD      TYPE             DEVICE SIZE/OFF       NODE NAME
process      123       user  cwd       DIR                8,1     4096          2 /path/to/directory

What needs to be noted

• ‘lsof’ provides extensive information, so it can be overwhelming at first. Start with basic usage and slowly incorporate more options as needed.
• The output of ‘lsof’ can be quite extensive. Use piping with ‘less’ or ‘more’ for easier reading.

Conclusion

‘lsof’ is a powerful and versatile command that is crucial for system administrators and developers. By mastering ‘lsof’, you can gain detailed insight into how your system’s resources are being used.