The program atop is an interactive monitor to view the load on a Linux system. It shows the occupation of the most critical hardware resources (from a performance point of view) on system level, i.e. cpu, memory, disk and network. It also shows which processes are responsible for the indicated load with respect to cpu- and memory load on process level. Disk load is shown if per process “storage accounting” is active in the kernel or if the kernel patch ‘cnt’ has been installed. Network load is only shown per process if the kernel patch ‘cnt’ has been installed.

Install atop on CentOS/RHEL/Red hat Linux using yum

First you need to enable EPEL repo as described here to install atop. Type the following yum command:
# yum install atop
Sample outputs:

Loaded plugins: product-id, protectbase, rhnplugin
This system is receiving updates from RHN Classic or RHN Satellite.
0 packages excluded due to repository protections
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package atop.x86_64 0:1.27-1.el6 will be installed
--> Finished Dependency Resolution
 
Dependencies Resolved
 
==================================================================
 Package     Arch          Version              Repository   Size
==================================================================
Installing:
 atop        x86_64        1.27-1.el6           epel        106 k
 
Transaction Summary
==================================================================
Install       1 Package(s)
 
Total download size: 106 k
Installed size: 229 k
Is this ok [y/N]: y
Downloading Packages:
atop-1.27-1.el6.x86_64.rpm                 | 106 kB     00:00     
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
  Installing : atop-1.27-1.el6.x86_64                         1/1 
  Verifying  : atop-1.27-1.el6.x86_64                         1/1 
 
Installed:
  atop.x86_64 0:1.27-1.el6                                        
 
Complete!

How do I use atop program?

Type the following command as root user:
# atop
Sample outputs:

atop command examples

Here are some conman atop command examples:

To see active processes only

# atop -a

Display individual threads

# atop -y

Display average-per-second i.s.o. total values

# atop -1

Display memory-related process-info
# atop -m

Display disk-related process-info

# atop -d

Display network-related process-info

# atop -n

Display scheduling-related process-info

# atop -s

Display various process-info (ppid, user/group, date/time)

# atop -v

Display command line per process

# atop -c

Sorting option

Pass the following option to sort your process:

	  -C  sort processes in order of cpu-consumption (default)
	  -M  sort processes in order of memory-consumption
	  -D  sort processes in order of disk-activity
	  -N  sort processes in order of network-activity
	  -A  sort processes in order of most active resource (auto mode)

See atop(1) for more information.