Fuser
Fuser is a command-line utility in Unix-like operating systems (including Linux and macOS) that identifies which processes are using specific files or sockets, helping diagnose issues like 'file in use' errors. It displays the process ID (PID), user, and command associated with the resource, making it useful for system administration and debugging. The tool is part of the psmisc package and is commonly pre-installed or available via package managers.
Developers should learn Fuser when working on Unix-based systems to troubleshoot problems where files or network sockets cannot be accessed due to being locked by other processes, such as during software deployment, server maintenance, or debugging application conflicts. It is particularly valuable in DevOps, system administration, and backend development scenarios where resource management is critical for ensuring system stability and performance.