Understanding 'top' Command Output Fields in Linux
Real-Time Process Monitoring
The top program is a dynamic view of the system’s processes, displaying a summary header followed by a process or thread list similar to ‘ps’ information. Unlike the static ps output, top continuously refreshes at a conﬁgurable interval, and provides capabilities for column reordering, sorting, and highlighting. User conﬁgurations can be saved and made persistent.
Default output columns are recognizable from other resource tools:
The process ID (PID).
User name (USER) is the process owner.
Virtual memory (VIRT) is all memory the process is using, including the resident set, shared libraries, and any mapped or swapped memory pages. (Labeled VSZ in the ps command.)
Resident memory (RES) is the physical memory used by the process, including any resident shared objects. (Labeled RSS in the ps command
Process state (S) displays as:
- D = Uninterruptible Sleeping
- R = Running or Runnable
- S = Sleeping
- T = Stopped or Traced
- Z = Zombie
CPU time (TIME) is the total processing time since the process started. May be toggled to include cumulative time of all previous children.
The process command name (COMMAND).
Fundamental Keystrokes in top
|? Or H||Help for interactive keystrokes.|
|L,T,M||Toggles for load, threads, and memory header lines.|
|1||Toggle showing individual CPUs or a summary for all CPUs in header.|
|S||Change the refresh (screen) rate, in decimal seconds (e.g., 0.5, 1, 5).|
|B||Toggle reverse highlighting for Running processes; default is bold only.|
|B||Enables use of bold in display, in the header, and for Running processes.|
|Shift+H||Toggle threads; show process summary or individual threads.|
|U, Shift+U||Filter for any user name (effective, real).|
|Shift+M||Sorts process listing by memory usage, in descending order.|
|Shift+P||Sorts process listing by processor utilization, in descending order.|
|K||Kill a process. When prompted, enter PID, then signal.|
|R||Renice a process. When prompted, enter PID, then nice_value.|
|Shift+W||Write (save) the current display configuration for use at the next top restart.|