top

top is an essential utility that provides real-time information about system performance and running processes. The top command displays system statistics, including CPU and memory usage, and provides a detailed list of running processes with various metrics.

Basic Syntax

top [options]

Commonly Used Options

• -d: Set the delay between updates (in seconds).
• -p: Monitor specific process IDs.
• -u: Monitor processes owned by a specific user.
• -k: Set the sort order for the displayed list of processes.
• -b: Run in batch mode (useful for logging to a file).
• -n: Set the number of iterations to run before exiting.
• -H: Show individual threads for each process.
• -i: Don’t display idle processes.
• -c: Show absolute path of the process command.

Examples of Using top Options

• top: Displays a continuously updating list of running processes and system performance metrics, sorted by CPU usage by default.
• top -d 5: Displays a continuously updating list of running processes and system performance metrics, with a 5 second delay between updates.
• top -u username: Displays a continuously updating list of running processes and system performance metrics, showing only processes owned by the specified user.
• top -p pid: Displays a continuously updating list of running processes and system performance metrics, showing only the process with the specified process ID.
• top -o %MEM: Displays a continuously updating list of running processes and system performance metrics, sorted by memory usage (with the highest usage at the top of the list).
• top -H: Displays a continuously updating list of running processes and system performance metrics, showing individual threads for each process.
• top -i: Displays a continuously updating list of running processes and system performance metrics, with idle processes hidden.
• top -c: Displays a continuously updating list of running processes and system performance metrics, showing the absolute path of the process command.

Displayed Metrics in top

• PID: The unique process ID.
• USER: The user who started the process.
• %CPU: The percentage of CPU time the process has used.
• %MEM: The percentage of physical memory the process has used.
• RES: The resident set size (i.e., the amount of physical memory) the process is using.
• VIRT: The virtual memory size of the process.
• SHR: The amount of shared memory used by the process.
• TIME+: The total CPU time the process has used.
• COMMAND: The command used to start the process.