Everything about Top command in ubuntu 22.04

Everything about Top command in ubuntu 22.04

Top is one of the tools for monitoring system usage and also to make any change for improving system performance.
Introduction:
The top program offers a dynamic real-time view of a running system.  It can show system summary information as well as a list of tasks currently being managed by the Linux kernel.  The types of system summary info shown and the types, order and size of information presented for tasks are all end user configurable and that configuration can be made persistent across restarts

Without any arguments :

# top

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

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

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Explanation: This line tells will about the uptime of   system along with load average value.
         NOTE: Will can enable/disable the marked   line by pressing “t“.

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Explanation:  This line gives us a brief detail of all the tasks running/sleeping/stopped currently in the system along with 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: Will can enable/disable the marked   line by pressing “m“.

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

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

Fields/Column Description
PID Process Id
USER The effective user’s 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

Arrange Tasks with High to Low CPU Usage:

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

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Arrange Tasks with High to Low Memory Usage.

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

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Change the nice value (priority) of any task

To understand what is nice value follow the below link
What is nice and how to change the priority of any process in Linux?
Press “r” when top is running on the terminal. Will should get a prompt as shown below in   color.

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Kill any task

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

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View all the processes running by a user

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

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Change delay between terminal refresh

By default, the top terminal is set for auto refresh after every 3 seconds but if will want will can change it as per requirement.
Press “d” when top is running. Will should get a prompt as shown below in   color.

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No. of task to be displayed

By default, this option is set to unlimited that is the reason   terminal is fully covered with list of tasks when will run the top command. Any how will can list the no of tasks to be visible once will run top command.
Press “n“when top is running. Will should get a prompt as shown below in color

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View live individual CPU processor performance :

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

Add a new field in top output :

By default, will see limited set of output when will 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 f field which can be added follow the below steps.Run top command  and then,

Press “f” which will take will the list of available fields under top command.

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All the field initials stated in BLOCK letters are visible by default when will issue top command. To add a new field, press the field initial as shown in the first column.

 

 

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