The top command in Linux is a powerful and widely used utility for monitoring system performance and resource usage in real-time. It provides users with a dynamic view of system activity, allowing them to observe how processes are utilizing CPU, memory, and other resources at any given moment. Here’s a detailed breakdown of its features and functionalities:

Table of Contents

Key Features of the top Command in linux
Normal Output of top command in Linux:
Using the Top Command in Linux to Arrange Tasks by CPU Usage: From Highest to Lowest
Using the Top Command in Linux to Arrange Tasks by Memory Usage: From Highest to Lowest
How to Change the Nice Value (Priority) of a Task in Linux
Killing a task without exiting from top command in linux:
top command to View all the processes running by a user:
Change delay between terminal refresh:
No. of task to be displayed:
View live individual CPU processor performance::
Add a new field in top output::
Conclusion

Key Features of the `top` Command in linux

Real-Time Monitoring: The top command updates its display at regular intervals (default is every 3 seconds), providing a live view of system performance. This allows users to quickly assess the current state of the system and identify any processes that may be consuming excessive resources.
System Summary Information: At the top of the top output, users can find summary information about the system, including:
- Uptime
- Load averages (over 1, 5, and 15 minutes)
- Total number of tasks (processes), along with their states (running, sleeping, etc.)
- CPU usage percentages (user, system, idle, etc.)
- Memory and swap usage statistics
Process List: Below the summary information, top displays a list of currently running processes. Each entry includes critical details such as:
- Process ID (PID)
- User who owns the process
- CPU and memory usage
- Process priority and nice value
- Time the process has been running
- Command that started the process
User Configurable Display: Users can customize the output of the top command to suit their needs. This includes:
- Changing the sorting order of processes (e.g., by CPU usage, memory usage, etc.)
- Selecting which columns to display and their order
- Filtering processes based on various criteria (e.g., by user or by command)
Interactive Commands: While running, top allows users to interact with it through various keyboard shortcuts. For example:
- Pressing k allows users to kill a process by entering its PID.
- Pressing r allows users to change the priority (nice value) of a process.
- Pressing h shows help information about the interactive commands available.
Configuration Persistence: Users can save their custom configurations, ensuring that their preferred settings are retained across sessions. This is particularly useful for users who frequently monitor system performance and want to maintain a consistent view.
Support for Multiple Displays: The top command can also support multiple displays, allowing users to view different sets of processes or customize views for various aspects of system performance.

Normal Output of top command in Linux:

top - 17:38:53 up  1:42,  0 users,  load average: 0.05, 0.02, 0.00
Tasks:  72 total,   1 running,  71 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.2 sy,  0.0 ni, 99.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24654.1 free,    239.8 used,    283.1 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24607.5 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     39 root      20   0 1868052  27808  10188 S   0.7   0.1   0:00.61 fail2ban-server
      1 root      20   0  168024  12008   9584 S   0.0   0.0   0:00.20 systemd
     21 root      20   0   26192  13480  12128 S   0.0   0.1   0:00.25 systemd-journal
     31 root      20   0  173356  24260  18040 S   0.0   0.1   0:00.03 php-fpm
     34 root      20   0  163896   5704   4988 S   0.0   0.0   0:00.20 rsyslogd
     35 root      20   0   16084   8548   7048 S   0.0   0.0   0:00.00 sshd
     41 root      20   0   23656  15872  12552 S   0.0   0.1   0:00.05 httpd
     42 root      20   0    6012   3544   2696 S   0.0   0.0   0:00.00 crond
     49 root      20   0   11972   1244     68 S   0.0   0.0   0:00.00 sw-cp-serverd
{altered}

Generally, we use top without any arguments, but the magic is mostly done from the top command line, which most of us skip. Well, before I take you to that part, let me explain the various system-related features that are shown by top command.

NOTE: We can enable or disable the marked red line by pressing “l” once top is running.

top - 17:38:53 up  1:42,  0 users,  load average: 0.05, 0.02, 0.00
Tasks:  72 total,   1 running,  71 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.2 sy,  0.0 ni, 99.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24654.1 free,    239.8 used,    283.1 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24607.5 avail Mem

Explanation: This line provides information about system’s uptime as well as the load average.

NOTE:We can enable/disable the marked red line by pressing “t“.

top - 17:59:01 up  2:02,  0 users,  load average: 0.03, 0.03, 0.00
Tasks:  49 total,   1 running,  48 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24674.6 free,    208.7 used,    293.7 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24630.5 avail Mem

Explanation: This line provides us with a brief summary of all the jobs that are now active, inactive, or stopped in the system, as well as the CPU usage.

Value	Meaning
us	user cpu time (or) % CPU time spent in user space
sy	system cpu time (or) % CPU time spent in kernel space
ni	user nice cpu time (or) % CPU time spent on low priority processes
id	idle cpu time (or) % CPU time spent idle
wa	io wait cpu time (or) % CPU time spent in wait (on disk)
hi	hardware irq (or) % CPU time spent servicing/handling hardware interrupts
si	software irq (or) % CPU time spent servicing/handling software interrupts
st	steal time – – % CPU time in involuntary wait by virtual cpu while hypervisor is servicing another processor (or) % CPU time stolen from a virtual machine

NOTE: We can enable/disable the marked red line by pressing “m“.

top - 17:59:01 up  2:02,  0 users,  load average: 0.03, 0.03, 0.00
Tasks:  49 total,   1 running,  48 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24674.6 free,    208.7 used,    293.7 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24630.5 avail Mem

Explanation:The next line shows memory(RAM and swap) usage and capacity.

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     21 root      20   0   42576  27236  25884 S   0.3   0.1   0:03.23 systemd-journal
     39 root      20   0 1868052  29916  10188 S   0.3   0.1   0:14.00 fail2ban-server
    380 postfix   20   0   45364   7352   6384 S   0.3   0.0   0:00.62 qmgr
    383 postfix   20   0   45332   8560   7492 S   0.3   0.0   0:00.08 trivial-rewrite
   2671 root      20   0    7872   3764   3164 R   0.3   0.0   0:00.28 top
      1 root      20   0  167904  11996   9584 S   0.0   0.0   0:02.57 systemd
     31 root      20   0  173356  24260  18040 S   0.0   0.1   0:00.18 php-fpm
     34 root      20   0  180276  12500  11708 S   0.0   0.0   0:02.53 rsyslogd
     35 root      20   0   16084   8548   7048 S   0.0   0.0   0:00.00 sshd
     41 root      20   0   23656  15872  12552 S   0.0   0.1   0:00.19 httpd
     42 root      20   0    6012   3560   2696 S   0.0   0.0   0:00.00 crond
     49 root      20   0   11972   1244     68 S   0.0   0.0   0:00.00 sw-cp-serverd
     50 sw-cp-s+  20   0   14824   4932   3384 S   0.0   0.0   0:00.00 sw-cp-serverd
     64 apache    20   0  175132  10732   4400 S   0.0   0.0   0:00.00 php-fpm

The left sections shows the details of the process running along with the below details.

Fields	Description
PID	Process Id
USER	The effective user name of the task’s owner
PR	The priority of the task
NI	The nice value of the task. A negative nice value means higher priority, whereas a positive nice value means lower priority. Zero in this field simply means priority will not be adjusted in determining a task’s dispatchability
%CPU	The task’s share of the elapsed CPU time since the last screen update, expressed as a percentage of total CPU time.
%MEM	A task’s currently used share of available physical memory
TIME+	Total CPU time the task has used since it started
S	The status of the task which can be one of: ‘D’ = uninterruptible sleep ‘R’ = running ‘S’ = sleeping ‘T’ = traced or stopped ‘Z’ = zombie
RES	The non-swapped physical memory a task has used
SHR	The amount of shared memory used by a task
Command	Display the command line used to start a task or the name of the associated program

Using the Top Command in Linux to Arrange Tasks by CPU Usage: From Highest to Lowest

Press “P” or shift+p” once top is running to arrange all the tasks with High to Low CPU Usage as shown below.

[root@TechArticles:~]# top
top - 18:29:08 up  2:33,  0 users,  load average: 1.34, 0.49, 0.17
Tasks:  49 total,   5 running,  44 sleeping,   0 stopped,   0 zombie
%Cpu(s): 49.6 us,  0.1 sy,  0.0 ni, 49.2 id,  0.0 wa,  0.0 hi,  1.0 si,  0.0 st
MiB Mem :  25177.0 total,  24597.9 free,    214.0 used,    365.2 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24624.3 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   4027 jay       20   0    6020   1844      0 R 100.0   0.0   0:07.64 bash
   4028 jay       20   0    6020   1844      0 R 100.0   0.0   0:07.64 bash
   4029 jay       20   0    6020   1844      0 R 100.0   0.0   0:07.64 bash
   4030 jay       20   0    6020   1844      0 R 100.0   0.0   0:07.64 bash
      1 root      20   0  168052  12016   9584 S   0.3   0.0   0:03.16 systemd
     21 root      20   0   42576  30040  28688 S   0.3   0.1   0:03.96 systemd-journal
     39 root      20   0 1868052  29916  10188 S   0.3   0.1   0:17.15 fail2ban-server
     31 root      20   0  173356  24260  18040 S   0.0   0.1   0:00.21 php-fpm

Using the Top Command in Linux to Arrange Tasks by Memory Usage: From Highest to Lowest

Press “M” or “shift+m“once top is running to arrange all the tasks with High to Low Memory Usage as shown below.

[root@TechArticles:~]# top
top - 18:35:02 up  2:38,  0 users,  load average: 1.43, 2.17, 1.13
Tasks:  46 total,   2 running,  44 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.5 us, 11.7 sy,  0.0 ni, 87.5 id,  0.0 wa,  0.0 hi,  0.4 si,  0.0 st
MiB Mem :  25177.0 total,   7031.2 free,  17779.9 used,    365.9 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.   7058.3 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   4406 jay       20   0   17.1g  17.1g   1860 R 100.0  69.6   0:10.09 tail
     21 root      20   0   42576  31104  29752 S   0.0   0.1   0:04.39 systemd-journal
     39 root      20   0 1868052  29916  10188 S   0.3   0.1   0:18.83 fail2ban-server
     31 root      20   0  173356  24260  18040 S   0.0   0.1   0:00.23 php-fpm
     74 apache    20   0 2524676  17992   5832 S   0.0   0.1   0:01.12 httpd
     75 apache    20   0 2327872  15940   5836 S   0.0   0.1   0:01.06 httpd
     78 apache    20   0 2262336  15940   5836 S   0.0   0.1   0:01.06 httpd
     41 root      20   0   23656  15872  12552 S   0.0   0.1   0:00.25 httpd
     34 root      20   0  180276  14880  14064 S   0.3   0.1   0:03.39 rsyslogd
      1 root      20   0  168052  12016   9584 S   0.0   0.0   0:03.53 systemd

How to Change the Nice Value (Priority) of a Task in Linux

In Linux, the nice value of a process determines its scheduling priority. A lower nice value means a higher priority, while a higher nice value means a lower priority. The default nice value is usually 0, and it can range from -20 (highest priority) to 19 (lowest priority).

Press “r” when top is running on the terminal. You should get a prompt as shown below in red color.

[root@TechArticles:~]# top
top - 18:42:37 up  2:46,  0 users,  load average: 0.03, 0.53, 0.72
Tasks:  46 total,   1 running,  45 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.1 sy,  0.0 ni, 99.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24586.9 free,    215.3 used,    374.9 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24614.9 avail Mem
PID to renice [default pid = 3896]
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   3896 jay       20   0    6536   5824   3452 S   0.0   0.0   0:00.02 bash
   4706 jay       20   0    7872   3888   3292 S   0.0   0.0   0:00.07 top

Give the PID which nice value has to be changed and hit “Enter”. Then give the nice value for the PID

top - 18:45:20 up  2:49,  0 users,  load average: 0.00, 0.31, 0.60
Tasks:  46 total,   1 running,  45 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.2 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24586.1 free,    215.7 used,    375.2 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24614.5 avail Mem
Renice PID 4706 to value -9
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   3896 jay       20   0    6536   5824   3452 S   0.0   0.0   0:00.02 bash
   4706 jay       20   0    7872   3888   3292 S   0.0   0.0   0:00.16 top

Renice PID 4706 to value: -9 [Hit Enter]

Verify the changes:

[root@TechArticles:~]# top
top - 18:48:22 up  2:52,  0 users,  load average: 0.00, 0.16, 0.49
Tasks:  77 total,   1 running,  76 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.2 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24549.1 free,    251.8 used,    376.1 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24578.1 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   3896 jay       20   0    6536   5824   3452 S   0.0   0.0   0:00.02 bash
   4706 jay       11  -9    7980   4000   3292 S   0.1   0.0   0:00.27 top

Killing a task without exiting from top command in linux:

Press “k” on the terminal when top is running. We should get a prompt as shown below in red color

[root@TechArticles:~]# top
top - 18:50:36 up  2:54,  0 users,  load average: 0.04, 0.12, 0.43
Tasks:  55 total,   1 running,  54 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.2 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24581.2 free,    219.5 used,    376.3 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24610.4 avail Mem
PID to signal/kill [default pid = 3896]
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   3896 jay       20   0    6536   5824   3452 S   0.0   0.0   0:00.02 bash
   4706 jay       20   0    7980   4000   3292 S   0.1   0.0   0:00.35 top

Type the PID you want to kill and Hit Enter as shown below. It will kill instantly relevent PID processes

[root@TechArticles:~]# top
top - 18:50:36 up  2:54,  0 users,  load average: 0.04, 0.12, 0.43
Tasks:  55 total,   1 running,  54 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.2 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24581.2 free,    219.5 used,    376.3 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.  24610.4 avail Mem
Send pid 4706 signal [15/sigterm]
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   3896 jay       20   0    6536   5824   3452 S   0.0   0.0   0:00.02 bash
   4706 jay       20   0    7980   4000   3292 S   0.1   0.0   0:00.35 top

top command to View all the processes running by a user:

Press “u” on the terminal when top is running. We should get a prompt as shown below in red color

[root@TechArticles:~]# top
top - 18:56:33 up  3:00,  0 users,  load average: 0.50, 0.20, 0.35
Tasks:  61 total,   2 running,  59 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.2 us,  1.0 sy,  0.0 ni, 98.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,    385.8 free,  24414.1 used,    377.1 buff/cache
MiB Swap:   7168.0 total,   7168.0 free,      0.0 used.    415.8 avail Mem
Which user (blank for all)
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   6170 jay       20   0   23.6g  23.6g   1752 R  91.7  95.9   0:33.84 tail
     21 root      20   0   50768  38112  36732 S   0.3   0.1   0:06.08 systemd-journal
     39 root      20   0 1868052  29928  10188 S   0.3   0.1   0:25.52 fail2ban-server
     78 apache    20   0 2262336  15940   5836 S   0.3   0.1   0:01.48 httpd
      1 root      20   0  168052  12032   9584 S   0.0   0.0   0:04.84 systemd
     31 root      20   0  173356  24260  18040 S   0.0   0.1   0:00.30 php-fpm
     34 root      20   0  188468  18460  17604 S   0.0   0.1   0:04.65 rsyslogd

Type the username that you want to show processes for.

[root@TechArticles:~]# top
top - 18:59:24 up  3:03,  0 users,  load average: 0.62, 0.39, 0.40
Tasks:  61 total,   3 running,  58 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.7 us, 14.9 sy,  0.0 ni, 79.5 id,  3.5 wa,  0.0 hi,  1.4 si,  0.0 st
MiB Mem :  25177.0 total,    168.7 free,  24961.8 used,     46.5 buff/cache
MiB Swap:   7168.0 total,   6683.9 free,    484.1 used.    100.6 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   6448 jay       20   0   24.6g  24.2g    428 R  81.8  98.3   0:12.45 tail
   6211 jay       20   0    7872    368      0 S   3.9   0.0   0:00.27 top
   3896 jay       20   0    6536      8      4 S   0.0   0.0   0:00.02 bash
   5959 jay       20   0    6020    180    180 S   0.0   0.0   0:00.02 bash

Change delay between terminal refresh:

By default the top terminal is set for auto refresh after every 3 seconds but if you want you can change it as per your requirement.

Press “d” when top is running. We should get a prompt as shown below in red color.

[jay@TechArticles ~]$ top
top - 19:02:21 up  3:06,  0 users,  load average: 0.35, 0.69, 0.55
Tasks:  59 total,   1 running,  58 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.1 sy,  0.0 ni, 99.8 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24805.2 free,    277.6 used,     94.2 buff/cache
MiB Swap:   7168.0 total,   6959.3 free,    208.7 used.  24629.4 avail Mem
Change delay from 3.0 to 2
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     34 root      20   0  196660  15064  14444 S   0.3   0.1   0:05.02 rsyslogd
     39 root      20   0 1868052   9316      0 S   0.3   0.0   0:27.84 fail2ban-server
    378 root      20   0   38112    108      0 S   0.3   0.0   0:01.88 master
    380 postfix   20   0   45364    164      0 S   0.3   0.0   0:01.30 qmgr

Verify the changes. You must see the screen buffer getting refresh much earlier or just to verify you can provide a higher value of delay and observer the refresh rate on the terminal

No. of task to be displayed:

By default this option is set to unlimited that is the reason your terminal is fully covered with list of tasks when you run the top command. Any how you can list the no of tasks to be visible once you run top command.

Press “n“when top is running. You should get a prompt as shown below in red color

[root@TechArticles:~]# top
top - 19:05:23 up  3:09,  0 users,  load average: 0.13, 0.41, 0.46
Tasks:  60 total,   1 running,  59 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24803.1 free,    278.6 used,     95.3 buff/cache
MiB Swap:   7168.0 total,   6960.3 free,    207.7 used.  24627.5 avail Mem
Maximum tasks = 0, change to (0 is unlimited)
    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
      1 root      20   0  167924   5524   4388 S   0.0   0.0   0:05.53 systemd
     21 root      20   0   58960  33164  32692 S   0.0   0.1   0:06.97 systemd-journal
     31 root      20   0  173356   3048    148 S   0.0   0.0   0:00.37 php-fpm
     34 root      20   0  196660  15444  14820 S   0.0   0.1   0:05.19 rsyslogd
     35 root      20   0   16084    664      0 S   0.0   0.0   0:00.00 sshd
     39 root      20   0 1868052   9316      0 S   0.0   0.0   0:28.67 fail2ban-server
     41 root      20   0   23656   2044   1004 S   0.0   0.0   0:00.38 httpd
     42 root      20   0    6012   1716   1160 S   0.0   0.0   0:00.01 crond
     [Output truncated]

Type the number of process you want to dispaly on top and hit enter. i.e I choose 3.

[jay@TechArticles:~]# top
top - 19:07:30 up  3:11,  0 users,  load average: 0.07, 0.29, 0.40
Tasks:  59 total,   1 running,  58 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.1 us,  0.2 sy,  0.0 ni, 99.5 id,  0.0 wa,  0.0 hi,  0.2 si,  0.0 st
MiB Mem :  25177.0 total,  24797.3 free,    280.9 used,     98.9 buff/cache
MiB Swap:   7168.0 total,   6960.8 free,    207.2 used.  24623.2 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     39 root      20   0 1868052  10572      0 S   0.3   0.0   0:29.23 fail2ban-server
    380 postfix   20   0   45364    164      0 S   0.3   0.0   0:01.37 qmgr
   6950 root      20   0    7872   3832   3236 R   0.3   0.0   0:00.01 top

View live individual CPU processor performance::

By default top command shows the average of all the available CPUs in the machine.

In case if you want to see report of all the individual CPUs press “1” once you are running top command and you will get to see something like below

[root@TechArticles:~]# top
top - 19:09:59 up  3:13,  0 users,  load average: 0.04, 0.20, 0.35
Tasks:  60 total,   1 running,  59 sleeping,   0 stopped,   0 zombie
%Cpu0  :  0.3 us,  0.3 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu1  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu2  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu3  :  0.7 us,  0.0 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu4  :  0.3 us,  0.3 sy,  0.0 ni, 99.3 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu5  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu6  :  0.3 us,  0.0 sy,  0.0 ni, 99.7 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
%Cpu7  :  0.0 us,  0.0 sy,  0.0 ni,100.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24796.4 free,    281.0 used,     99.7 buff/cache
MiB Swap:   7168.0 total,   6961.3 free,    206.7 used.  24622.5 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
     39 root      20   0 1868052  10572      0 S   0.7   0.0   0:29.91 fail2ban-server
      1 root      20   0  167924   5728   4548 S   0.0   0.0   0:05.80 systemd
    41 root      20   0   23656   2044   1004 S   0.0   0.0   0:00.39 httpd

Add a new field in top output::

By default we see limited set of output when use the top command. But apart from those there are a other list of field which can be added to the top output. To view all the list of field which can be added, Follow the below steps.

Run top command
then Press “f” which will take you the list of available fields under top command.
All the field initials stated in BLOCK letters are visible by default when you issue top command. To add a new field press the field initial as shown in the first column.

Fields Management for window 1:Def, whose current sort field is %CPU
	Navigate with Up/Dn, Right selects for move then <Enter> or Left commits,
	'd' or <Space> toggles display, 's' sets sort. Use 'q' or <Esc> to end!

* PID     = Process Id             DATA    = Data+Stack (KiB)
* USER    = Effective User Name    nMaj    = Major Page Faults
* PR      = Priority               nMin    = Minor Page Faults
* NI      = Nice Value             nDRT    = Dirty Pages Count
* VIRT    = Virtual Image (KiB)    WCHAN   = Sleeping in Function
* RES     = Resident Size (KiB)    Flags   = Task Flags <sched.h>
* SHR     = Shared Memory (KiB)    CGROUPS = Control Groups
* S       = Process Status         SUPGIDS = Supp Groups IDs
* %CPU    = CPU Usage              SUPGRPS = Supp Groups Names
* %MEM    = Memory Usage (RES)     TGID    = Thread Group Id
* TIME+   = CPU Time, hundredths   OOMa    = OOMEM Adjustment
* COMMAND = Command Name/Line      OOMs    = OOMEM Score current
  PPID    = Parent Process pid     ENVIRON = Environment vars
  UID     = Effective User Id      vMj     = Major Faults delta
  RUID    = Real User Id           vMn     = Minor Faults delta
  RUSER   = Real User Name         USED    = Res+Swap Size (KiB)
  SUID    = Saved User Id          nsIPC   = IPC namespace Inode
  SUSER   = Saved User Name        nsMNT   = MNT namespace Inode
  GID     = Group Id               nsNET   = NET namespace Inode
  GROUP   = Group Name             nsPID   = PID namespace Inode
  PGRP    = Process Group Id       nsUSER  = USER namespace Inode
  TTY     = Controlling Tty        nsUTS   = UTS namespace Inode
  TPGID   = Tty Process Grp Id     LXC     = LXC container name
  SID     = Session Id             RSan    = RES Anonymous (KiB)
  nTH     = Number of Threads      RSfd    = RES File-based (KiB)
  P       = Last Used Cpu (SMP)    RSlk    = RES Locked (KiB)
  TIME    = CPU Time               RSsh    = RES Shared (KiB)
  SWAP    = Swapped Size (KiB)     CGNAME  = Control Group name
  CODE    = Code Size (KiB)        NU      = Last Used NUMA node

Fields Management for window 1:Def, whose current sort field is %CPU
Navigate with Up/Dn, Right selects for move then <Enter> or Left commits,
‘d’ or <Space> toggles display, ‘s’ sets sort. Use ‘q’ or <Esc> to end!

To add the “swap” field, for example, user “down arrow key and highlight swap then press space key to select and Press “q” or esc to return to the top output. You will see something similar to the image below.

top - 19:37:09 up  3:41,  0 users,  load average: 0.02, 0.01, 0.06
Tasks:  50 total,   1 running,  49 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.2 us,  0.3 sy,  0.0 ni, 99.5 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
MiB Mem :  25177.0 total,  24782.9 free,    279.1 used,    115.1 buff/cache
MiB Swap:   7168.0 total,   6965.3 free,    202.7 used.  24611.9 avail Mem

    PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM COMMAND            SWAP     TIME+
     21 root      20   0   75344  43552  43080 S   0.3   0.2 systemd-journal     908   0:09.49
     39 root      20   0 1868052  10836      0 S   0.3   0.0 fail2ban-server    9152   0:38.79
     78 apache    20   0 2262336    612     92 S   0.3   0.0 httpd              9588   0:02.28
    378 root      20   0   38112    832    720 S   0.3   0.0 master              356   0:02.64
      1 root      20   0  167924   5732   4548 S   0.0   0.0 systemd            1244   0:07.53
     31 root      20   0  173356   3048    148 S   0.0   0.0 php-fpm            3324   0:00.49
     34 root      20   0  213044  20884  20188 S   0.0   0.1 rsyslogd            240   0:07.08
     35 root      20   0   16084    664      0 S   0.0   0.0 sshd                836   0:00.00
     41 root      20   0   23656   2044   1004 S   0.0   0.0 httpd              2280   0:00.49
     42 root      20   0    6012   1904   1344 S   0.0   0.0 crond               304   0:00.01
[Output Trancated]

Conclusion

The top command in linux is an essential tool for anyone managing a Linux or Unix system. Its ability to provide real-time insights into system performance and resource utilization makes it invaluable for monitoring, troubleshooting, and optimizing system operations. Whether you are a seasoned system administrator or a casual user, mastering the top command can significantly enhance your ability to manage and maintain a healthy system.

Reference: https://man7.org/linux/man-pages/man1/top.1.html

top command in Linux with Examples

Key Features of the `top` Command in linux

Normal Output of top command in Linux:

Using the Top Command in Linux to Arrange Tasks by CPU Usage: From Highest to Lowest

Using the Top Command in Linux to Arrange Tasks by Memory Usage: From Highest to Lowest

How to Change the Nice Value (Priority) of a Task in Linux

Killing a task without exiting from top command in linux:

top command to View all the processes running by a user:

Change delay between terminal refresh:

No. of task to be displayed:

View live individual CPU processor performance::

Add a new field in top output::

Conclusion

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Key Features of the top Command in linux

Normal Output of top command in Linux:

Using the Top Command in Linux to Arrange Tasks by CPU Usage: From Highest to Lowest

Using the Top Command in Linux to Arrange Tasks by Memory Usage: From Highest to Lowest

How to Change the Nice Value (Priority) of a Task in Linux

Killing a task without exiting from top command in linux:

top command to View all the processes running by a user:

Change delay between terminal refresh:

No. of task to be displayed:

View live individual CPU processor performance::

Add a new field in top output::

Conclusion

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Key Features of the `top` Command in linux