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Top command in detail on Linux

What is Top command?

top command shows a list of processes running in your system.It gives the summary on the top,how much of your system resources are being utilised.It displays number of processes running,cpu status,free memory, PID of program,user priority, uptime,memory and cpu usage etc.

The top program provides a dynamic real-time view of a running system. It can display system summary information as well as a list of processes or threads currently being managed by the Linux kernel. The types of system summary information shown and the types, order and size of information displayed for processes are all user configurable and that configuration can be made persistent across restarts.

The program provides a limited interactive interface for process manipulation as well as a much more extensive interface for personal configuration.Open you terminal and type top

root@seven:~# top
top - 09:05:51 up  1:13,  1 user,  load average: 0.72, 0.32, 0.28
Tasks: 149 total,   1 running, 147 sleeping,   0 stopped,   1 zombie
%Cpu(s): 11.9 us,  2.1 sy,  0.0 ni, 85.9 id,  0.0 wa,  0.0 hi,  0.1 si,  0.0 st
KiB Mem:   1908416 total,  1128268 used,   780148 free,   126172 buffers
KiB Swap:  1113084 total,        0 used,  1113084 free.   498036 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND     
 1156 root      20   0 2073284 232168  68632 S  56.5 12.2   1:56.49 gnome-shell 
  838 root      20   0  250328  35120  19392 S   6.0  1.8   0:04.54 Xorg        
 2150 root      20   0  441192  30028  23376 S   1.0  1.6   0:01.28 gnome-term+ 
    7 root      20   0       0      0      0 S   0.3  0.0   0:03.77 rcu_sched   
 1222 root      20   0 2441772  57392  21152 S   0.3  3.0   0:06.91 java        
 2160 root      20   0   25688   2984   2480 R   0.3  0.2   0:00.06 top         
    1 root      20   0  176152   5132   3088 S   0.0  0.3   0:01.65 systemd     
    2 root      20   0       0      0      0 S   0.0  0.0   0:00.00 kthreadd 

As you can see it is showing active and idle processes as well as cpu and memory usage,uptime etc.

Hide the idle processes

Just press i on your keyboard all the idle processes will be hidden and running processes will be shown.

i

Sort the processes according to memory usage

SHIFT + M command sort processes according to the memory usage.Process consuming highest memory will be listed first.

SHIFT + M

Sort the processes according to cpu usage

SHIFT + p will list the processes first on the basis of cpu usage.

SHIFT + P

SHIFT + W

The above command saves the top's output into a file.File will be saved in the home directory under the name of toprc.By default file will be hidden press CTR + H to make hidden files and directories visible.

1

One shows the detials of individual cpu's running on the system.

z

Z displays the running processes in colours.

d

d option allows us to change refreshing time.By default it refreshes in every 3 seconds,but you can customize it the way you want.

k

with k command you can you can kill processes.You must supply PID(Process ID) to it. You can obtain PID from the first column.Syntax:pid id

A

A command splits top's output into multiple screens.

c

c displays the absolute path of the running processes.Check the last column command

n

With n we can reduce the number of process to n numbers.

h 

h is for help.It displays all the options that you can use with top.

d 

SHIFT+A 

Splits top output into multiple screens