Top: The ‘Top’ command
provides a real time view of the running system. It can display system summary
information as well as list of tasks running currently.
A basic execution of ‘top’
command gives,
localhost: root-~ $ top
top - 23:24:28 up 100 days,
23:30, 1 users, load average: 3.64, 4.27, 3.94
Tasks: 97 total,
1 running, 96 sleeping, 0 stopped,
0 zombie
Cpu(s): 45.9%us, 0.0%sy,
0.0%ni, 53.9%id, 0.2%wa, 0.0%hi,
0.0%si, 0.0%st
Mem: 4194304k total, 4116216k used, 78088k free, 666688k buffers
Swap: 4194296k total, 52k used, 4194244k free, 719448k cached
PID USER
PR NI VIRT RES
SHR S %CPU %MEM
TIME+ COMMAND
3833 root
21 0 2457m 2.1g
9920 S
91.8 53.2 84027:12 java
1 root
15 0 10364 640 548 S 0.0 0.0 0:07.51 init
2 root
RT -5
0 0
0 S 0.0 0.0 0:01.10
migration/0
3 root
34 19
0 0 0 S 0.0 0.0
0:00.46 ksoftirqd/0
4 root
RT -5
0 0
0 S 0.0 0.0 0:00.00 watftirqd/0
Let’s see the output of the
command,
top - 23:24:28 up 100 days, 23:30, 0 users,
load average: 3.64, 4.27, 3.94
23:24:28: Current System Time
( can be obtained by ‘date’ command )
100 days: Up time, The System
was started before 100 days ( can get the same using ‘uptime’ command)
1 Users: One user
Load average 3.64, 4.27, 3.94: The Load Average displayed for past 1min,
5min and 15 minute intervals.
Tasks: 97 total, 1 running, 96 sleeping, 0 stopped,
0 zombie
Total Number of tasks: 97
Running: This can be a taught
as tasks that are ready to run.
Sleeping: by default sleeping
process don’t use any cpu.
Cpu(s): 45.9%us, 0.0%sy, 0.0%ni, 53.9%id, 0.2%wa, 0.0%hi,
0.0%si, 0.0%st
This section Says about the
CPU Details. This gives information on what cpu has spending time.
·
us -> User CPU time: The time the CPU has spent running users’ processes that are
not niced.
·
sy -> System CPU time: The time the CPU has spent running the kernel and its
processes.
·
ni -> Nice CPU time: The time the CPU has spent running users’ process that have
been niced.
·
wa -> iowait: Amount of time the CPU has been waiting for I/O to complete.
·
hi -> Hardware IRQ: The amount of time the CPU has been servicing hardware
interrupts.
·
si -> Software
Interrupts.: The amount of time the CPU has been
servicing software interrupts.
·
id is idle, in other words CPU idle status
·
st is Time stolen from a virtual machine
Mem: 4194304k total,
4116216k used, 78088k free, 666688k buffers
Swap: 4194296k
total, 52k used, 4194244k
free, 719448k cached
These give us the Details of the Memory
and Swap.
PID USER PR NI VIRT
RES SHR S %CPU %MEM
IME+ COMMAND
3833 root 21
0 2457m 2.1g 9920
S 91.8
53.2 84027:12 java
These details give you the Process
information. The columns indicate
1.
PID - Process ID - The unique
ID of the process (commonly used with the kill command)
2.
USER - Username which the
process is running under
3.
PR - Priority for the process
(ranges from -20 for very important processes to 19 for
unimportant processes)
4.
NI - Nice value modifies the
priority of the process (a negative value will increase the priority of the
process and a positive value will decrease the priority of the process)
5.
VIRT - Total amount of virtual
memory used by the process
6.
RES - Resident size (kb) -
Non-swapped physical memory which the process has used
7.
SHR - Shared memory size (kb) -
Amount of shared memory which the process has used (shared memory is memory
which could be allocated to other processes)
8.
S - Process status - Possible
values:
o R - Running
o D -
Sleeping (may not be interrupted)
o S -
Sleeping (may be interrupted)
o T - Traced
or stopped
o Z - Zombie
or "hung" process
9.
%CPU - Percentage of CPU time
the process was using at the time top last
updated
10.
%MEM - Percentage of memory
(RAM) the process was using at the time top last
updated
11.
TIME+ - Cumulative CPU time which
the process and children of the process have used
12.
COMMAND - Name of the process or
the path to the command used to start the process (press c to toggle
between the name of the process and the path to the command used to start the
process)
To sort top output by any column
In Order to sort the top
command output by any column, execute the top command and press ‘o’.It then
provides you with a list of options to sort .
Some of them
are
* A: PID =
Process Id
* E: USER = User
Name
* H: PR =
Priority
* I: NI =
Nice value
* O: VIRT = Virtual
Image (kb)
* Q: RES = Resident
size (kb)
Display Selected User Process In Top
In Order to get
the Details of a process that belong to a selected users, we can use
Top –u root
Display Only
Specific Process
If we need to
find the information about a specific process, we can use
top -p 29547(PID)
Refresh Linux Top Command Output
By default, the
output of the top command will be refreshed for every 3.0 seconds. If we need
to change this feature we can press ‘d’
while the top command is running. It allows us to enter the time frame for the
refresh rate.
High Light Running process
We can high
light the information a top command shows by pressing ‘z’ while the top command
is executing.
Display Absolute Path of the Command
If we need to
check the complete absolute path of the command that was executing in top command,
we can press ‘c’.
Decrease the Process Display Count in Top
If We need to
decrease the display of the process count in the output of top command, we can
press ‘n’ while the top command is executing. It gives us an option to enter a
value for the display of the process.
Write to a File
If we need to
write the Output of the top command to a file for future reference ,we can use
‘w’ while the top command is executing.The contents are saved to ~/.toproc
file.
top - 02:57:54 up 102 days,
3:08, 0 users, load average: 0.16, 0.16, 0.16
Tasks: 106 total, 1
running, 105 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.3%us, 0.5%sy,
0.0%ni, 97.4%id, 1.7%wa, 0.0%hi,
0.2%si, 0.0%st
Mem: 4194304k
total, 3595660k used, 598644k free, 706288k buffers
Swap: 4194296k total, 52k used,
4194244k free, 600820k cached
Wrote configuration to
'/privdir/djbs002/.toprc'
Once the file
is written it shows the confirmation.
There will be a
mode available in top command, which allows performing more tasks. Tasks like
- k, to kill a task
(process/thread)
- r, to re-nice a task
- d or s,
to change the delay or sleep interval
Consider if you
want to kill a process, when the top command was executing you can press ‘k’
which will ask you for the process ID to be killed. Once you enter PID and
enter , the process id will be killed.
