What is top

top is the standard Linux tool for monitoring running processes in real time. It updates every few seconds and shows CPU usage, memory usage, load average, and a ranked list of processes. It is available on every Linux system without installing anything.

Start top

top

Press q to quit.

Reading the header

The first lines show system-wide statistics:

top - 10:32:01 up 5 days,  3:14,  2 users,  load average: 0.42, 0.38, 0.35
Tasks: 142 total,   1 running, 141 sleeping,   0 stopped,   0 zombie
%Cpu(s):  3.2 us,  1.1 sy,  0.0 ni, 95.4 id,  0.2 wa,  0.0 hi,  0.1 si
MiB Mem :   7871.8 total,   3201.4 free,   2104.2 used,   2566.2 buff/cache
MiB Swap:   2048.0 total,   2048.0 free,      0.0 used.   5431.1 avail Mem

Key values:

  • load average — system load over the last 1, 5, and 15 minutes. Values above the number of CPU cores indicate saturation.
  • %Cpu — us (user), sy (kernel), id (idle), wa (waiting for I/O)
  • buff/cache — memory used for disk cache; Linux reclaims it when processes need more RAM

Process table columns

Column Meaning
PID Process ID
USER Owner
PR Priority
NI Nice value (negative = higher priority)
VIRT Total virtual memory
RES Resident (physical) memory in use
%CPU CPU share since last update
%MEM Physical memory share
TIME+ Total CPU time used
COMMAND Process name

Interactive commands

While top is running you can press keys to change behavior:

Key Action
q Quit
M Sort by memory usage
P Sort by CPU usage (default)
T Sort by time
u Filter by user (enter username)
k Kill a process (enter PID)
r Renice a process (change priority)
1 Toggle per-CPU stats
d Change update interval
Space Refresh immediately
h Help

Useful options

top -u username         show only processes owned by a user
top -p 1234,5678        monitor specific PIDs
top -d 5                set update interval to 5 seconds
top -n 3                run 3 iterations and exit (useful in scripts)
top -b -n 1             batch mode, one snapshot (pipe-friendly)

Capture a process snapshot to a file:

top -b -n 1 > top-snapshot.txt

Find what is eating CPU or RAM

Sort by CPU: press P (default on startup). Sort by memory: press M.

To check a specific process:

top -p $(pgrep nginx)

See also

If top feels dated, try htop — it has color, mouse support, and easier sorting. Install it with apt install htop or dnf install htop.

man top for the full reference.

  • Created: June 25, 2007
  • Last edited: July 7, 2026