<span>top</span> is a commonly used command-line tool in Linux systems for dynamically monitoring system resource usage in real-time. It displays the resource usage of various processes in the system (such as CPU and memory usage) and provides some interactive operation features.
📌 Basic Syntax
top
After running, you will see an interface similar to the following:
top - 14:30:00 up 2 days, 3:15, 1 user, load average: 0.15, 0.08, 0.05
Tasks: 150 total, 1 running, 149 sleeping, 0 stopped, 0 zombie
%Cpu(s): 2.3 us, 1.2 sy, 0.0 ni, 96.5 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
MiB Mem : 3945.2 total, 450.1 free, 2120.3 used, 1374.8 buff/cache
MiB Swap: 2048.0 total, 2048.0 free, 0.0 used. 1500.5 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1234 user 20 0 500000 30000 15000 S 5.6 0.7 1:23.45 firefox
🧾 Common Functions and Parameter Descriptions
1. Default Run
top
Displays the real-time resource usage of all processes in the system.
2. Display Processes of a Specific User
top -u username
Only displays the processes of a specific user, for example:
top -u www-data
3. Sort by Memory Usage
Press the <span>M</span> key to sort by memory usage percentage.
4. Sort by CPU Usage (Default)
Press the <span>P</span> key to sort by CPU usage rate.
5. Display Threads
top -H
Can view the thread status under each process (can also switch by pressing the <span>H</span> key).
6. Set Refresh Interval (Seconds)
top -d 5
Sets the refresh interval to every 5 seconds, the default is 3 seconds.
7. Display Process of a Specific PID
top -p 1234
Only displays the process of the specified PID. Multiple PIDs can be separated by commas:
top -p 1234,5678
8. Quiet Mode (for Scripts)
top -b
Suitable for scripts or logging, exits after outputting once.
For example, save to a file:
top -b -n 1 > top_output.txt
9. Exit <span>top</span>
Press the <span>q</span> key to exit.
🛠️ Common Interactive Commands (Key Presses During Runtime)
| Key | Function |
|---|---|
<span>P</span> |
Sort by CPU usage |
<span>M</span> |
Sort by memory usage |
<span>T</span> |
Sort by running time |
<span>1</span> |
Display usage for each CPU (multi-core) |
<span>H</span> |
Display threads |
<span>k</span> |
Kill process (input PID) |
<span>r</span> |
Adjust process priority (nice value) |
<span>q</span> |
Exit top |
✅ Example Use Cases
Check Which Process is Using the Most CPU
Run <span>top</span> and press <span>P</span> to sort.
Check the Process with the Highest Memory Usage
Run <span>top</span> and press <span>M</span> to sort.
Monitor a Specific Process
top -p $(pgrep nginx | tr '
' ',')
📌 Recommended Alternative Tools
<span>htop</span>: A more powerful and user-friendly alternative (requires installation).sudo apt install htop # Debian/Ubuntu sudo dnf install htop # Fedora