The top command can view the usage of Linux system resources in real time. 1. Enter top to open the interface through the terminal to open the interface, and the top displays a summary of the system running status, including load, number of tasks, CPU and memory usage; 2. The process list is sorted by CPU usage by default, which can identify highly occupant processes; 3. Shortcut keys such as P (CPU sort), M (memory sort), k (end process), r (adjust priority), and 1 (multi-core details) to improve operation efficiency; 4. Use top -b -n 1 to save output to a file; 5. Add the -u parameter to filter specific user processes. Mastering these key points can quickly locate performance issues.
When you want to quickly understand the current resource usage of Linux systems, top
command is a very practical tool. It can display the usage of CPU, memory and other resources by each process in the system in real time, and is the first choice for troubleshooting performance issues and monitoring server status.
How to interpret the top interface
After opening the terminal and entering top
to enter, you will see a dynamically updated interface, which is roughly divided into two parts: the status summary at the top and the process list below.
- The first line shows the system running time, number of users, and load average. If this value continues to be higher than the number of CPU cores, it means that the system may have been overloaded.
- The second and third lines show the total number of tasks, running tasks, and CPU usage, respectively. Pay special attention to
%id
(immersive CPU ratio) and%wa
(waiting for I/O time). - The fourth and fifth lines are the usage of memory and swap partitions. If you find that
buff/cache
is very high, you don’t have to worry too much, this part of the memory will be released when needed.
The process list is sorted by CPU usage by default. PID is the process ID. %CPU and %MEM represent the CPU and memory ratios used by the process respectively.
Common operations and shortcut keys
When running top
, you can do some interaction via the keyboard:
- P : Sort by CPU usage (default)
- M : Sort by memory usage
- k : After entering PID, a process can be terminated
- r : reset process priority (nice value)
- 1 : Expand to display the usage of each CPU core (for multi-core machines)
These shortcut keys do not require rote memorization, and they will naturally become familiar if you use them too much. For example, if you find that the server suddenly stutters, you can first press 1
to see if a certain core is fully loaded, and then press M
to find the process with the highest memory footprint.
Custom display and batch modes
Sometimes you don't want to enter the interactive interface, but instead want to save the output of top or pass it to other commands for processing. You can use batch mode at this time:
top -b -n 1 > top_output.txt
The above command will run top once and save the result to a file. -b
means batch mode, -n 1
means refreshing only once.
If you want to only look at the processes of a specific user, you can add the -u username
parameter at startup, so that you can filter out other people's processes and focus on viewing the parts you care about.
Basically that's it. Although top
is an old tool, it has a complete function. The key is to master a few common operations to cope with most daily needs. Novice may feel that there is too much information at the beginning, but as long as you grasp the key indicators, you can slowly see the trick.
The above is the detailed content of How to use the top command. For more information, please follow other related articles on the PHP Chinese website!

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