How to use the command top (with examples)
- Linux
- December 25, 2023
The top command is a powerful tool that allows you to monitor the real-time information about running processes on your system. It provides a dynamic, interactive interface that displays the CPU usage, memory usage, and other details of each running process. This article will illustrate various use cases of the top command with examples.
Use case 1: Start top
Code:
top
Motivation: Starting the top command without any arguments will launch the interactive interface that displays the real-time information about running processes. This is useful when you want to monitor the system activity continuously.
Explanation: In this use case, no arguments are passed to the top command.
Example output:
top - 15:49:02 up 2 days, 3:57, 2 users, load average: 0.52, 0.67, 0.79
Tasks: 183 total, 1 running, 182 sleeping, 0 stopped, 0 zombie
%Cpu(s): 6.7 us, 2.9 sy, 0.1 ni, 90.1 id, 0.0 wa, 0.0 hi, 0.0 si, 0.2 st
KiB Mem : 16328820 total, 14457812 free, 657348 used, 1213628 buff/cache
KiB Swap: 2097148 total, 2061456 free, 35692 used. 15549512 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 185040 4064 2824 S 0.0 0.0 0:03.40 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:01.41 ksoftirqd/0
4 root 20 0 0 0 0 S 0.0 0.0 0:01.19 kworker/0:0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
Use case 2: Do not show any idle or zombie processes
Code:
top -i
Motivation: By default, the top command displays all running processes, including idle and zombie processes. However, in some cases, you might want to exclude these processes from the output to focus only on actively running processes. The -i option allows you to achieve this.
Explanation: In this use case, the -i option is passed to the top command, which instructs it to not display any idle or zombie processes.
Example output:
top - 16:02:54 up 2 days, 4:10, 2 users, load average: 0.89, 0.94, 0.92
Tasks: 182 total, 1 running, 181 sleeping, 0 stopped, 0 zombie
%Cpu(s): 14.7 us, 8.6 sy, 0.0 ni, 76.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 16328820 total, 14462844 free, 654864 used, 1214112 buff/cache
KiB Swap: 2097148 total, 2061456 free, 35692 used. 15562140 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1385 root 20 0 253228 7456 5888 S 3.0 0.0 2:08.71 Xorg
2992 user 20 0 1378500 153556 86188 S 1.0 0.9 1:03.86 gnome-shell
2048 user 20 0 9151552 201040 110044 S 0.0 1.2 2:16.95 chrome
3253 user 20 0 2748480 446224 104692 S 0.0 2.7 2:25.13 code
Use case 3: Show only processes owned by given user
Code:
top -u username
Motivation: Sometimes you may want to focus on the processes owned by a specific user rather than seeing all the running processes. The -u option allows you to filter the output and display only the processes owned by the given user.
Explanation: In this use case, the -u option is used along with the username argument, where username represents the desired user.
Example output:
top - 16:12:21 up 2 days, 4:19, 2 users, load average: 0.74, 0.87, 0.90
Tasks: 144 total, 1 running, 143 sleeping, 0 stopped, 0 zombie
%Cpu(s): 20.2 us, 12.7 sy, 0.0 ni, 66.9 id, 0.0 wa, 0.0 hi, 0.2 si, 0.0 st
KiB Mem : 16328820 total, 14456592 free, 673612 used, 1235568 buff/cache
KiB Swap: 2097148 total, 2061456 free, 35692 used. 15526896 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1669 user 20 0 3910944 678188 57736 S 6.7 4.2 6:23.84 java
1942 user 20 0 2769356 862216 127040 S 2.3 5.3 8:52.73 code
2069 user 20 0 6466960 717968 77640 S 1.3 4.4 13:23.90 chrome
Use case 4: Sort processes by a field
Code:
top -o field_name
Motivation: By default, the top command sorts the processes by CPU usage. However, in some situations, you may want to sort the processes based on a different field, such as memory usage or process ID. The -o option allows you to specify the field for sorting.
Explanation: In this use case, the -o option is used along with the field_name argument, where field_name represents the desired field for sorting.
Example output:
top - 16:20:46 up 2 days, 4:28, 2 users, load average: 1.18, 1.26, 1.22
Tasks: 135 total, 1 running, 134 sleeping, 0 stopped, 0 zombie
%Cpu(s): 9.9 us, 5.2 sy, 0.0 ni, 84.7 id, 0.0 wa, 0.0 hi, 0.2 si, 0.0 st
KiB Mem : 16328820 total, 14458656 free, 684400 used, 1223764 buff/cache
KiB Swap: 2097148 total, 2060896 free, 36252 used. 15519476 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
122 root 20 0 0 0 0 R 0.7 0.0 0:07.80 kworker/4:1
2951 user 20 0 1375020 151796 84316 S 1.0 0.9 0:40.78 gnome-shell
388 root 20 0 60696 5696 4940 S 0.0 0.0 0:02.95 systemd-journal
439 root 20 0 0 0 0 I 0.0 0.0 0:02.13 kworker/u16:3
Use case 5: Show the individual threads of a given process
Code:
top -Hp process_id
Motivation: In some cases, you may want to analyze the individual threads of a specific process rather than seeing the overall process information. The -H option allows you to display the individual threads associated with a given process.
Explanation: In this use case, the -H option is passed to the top command along with the process_id argument, where process_id represents the ID of the process.
Example output:
top - 16:30:02 up 2 days, 4:37, 2 users, load average: 1.27, 1.26, 1.23
Tasks: 158 total, 2 running, 156 sleeping, 0 stopped, 0 zombie
%Cpu(s): 8.2 us, 3.7 sy, 0.0 ni, 88.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.1 st
KiB Mem : 16328820 total, 14471120 free, 672932 used, 1224692 buff/cache
KiB Swap: 2097148 total, 2060896 free, 36252 used. 15530920 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
319 root 20 0 0 0 0 S 5.7 0.0 0:36.65 kworker/0:1
922 user 20 0 7531852 643408 59048 R 2.2 4.0 18:13.84 chrome
920 user 20 0 3537348 174956 91884 R 0.7 1.1 4:25.41 chrome
10 root 20 0 0 0 0 I 0.3 0.0 0:52.67 rcu_gp
Use case 6: Show only the processes with the given PID(s), passed as a comma-separated list
Code:
top -p $(pgrep -d ',' process_name)
Motivation: Normally, you wouldn’t know the process IDs (PIDs) off hand. However, in some cases, you might want to monitor specific processes by their names. This use case demonstrates how to find the PIDs corresponding to a process name using pgrep and then pass them as an argument to the top command.
Explanation: In this use case, the -p option is used along with the process IDs obtained from the pgrep command. The pgrep -d ',' process_name command lists the PIDs of the processes with the given process_name and separates them by commas.
Example output:
top - 16:40:33 up 2 days, 4:48, 2 users, load average: 0.93, 1.10, 1.17
Tasks: 176 total, 1 running, 175 sleeping, 0 stopped, 0 zombie
%Cpu(s): 17.4 us, 9.5 sy, 0.0 ni, 73.0 id, 0.0 wa,
