atop – For Linux server performance analysis

We’re all familiar with top, a real-time system monitor. Some prefer htop and previously, I mentioned iotop for use with storage read/write monitoring. Let’s look at another popular tool for Linux server performance analysis: atop.

Advantages of atop

Atop is an ASCII full-screen performance monitor which can log and report the activity of all server processes. One feature I really like is that atop will stay active in the background for long-term server analysis (up to 28 days by default). Other advantages include:

• Shows resource usage of ALL processes, even those that are closed/completed.
• Monitors threads within processes & ignores unused processes.
• Accumulates resource usage for all processes and users with the same name.
• Highlights critical resources using colors (red).
• Will add or remove columns as the size of the display window changes.
• Includes disk I/O and network utilization.
• Uses netatop kernel module to monitor TCP & UDP and network bandwidth.

Once atop is launched, by default, it will show system activity for CPU, memory, swap, disks, and network in 10-second intervals. In addition, for each process and thread, you can analyze CPU utilization, memory consumption, disk I/O, priority, username, state, and even exit codes.

Install atop on RHEL/CentOS/Fedora Linux

First, install and enable EPEL (Extra Packages for Enterprise Linux) repo. See RedHat solution #308983.

dnf install atop

Install atop on Debian/Ubuntu Linux

apt install atop

Once installed on any distro, you can launch it similarly to top using:

atop

Using atop – system & process monitor

A good place to start would be to read the man pages:

man atop

Other useful commands:

Launch with average-per-second total values:

atop -1

Launch with active processes only:

atop -a

Launch with command line per process

atop -c

Launch with disk info

atop -d

Launch with memory info

atop -m

Launch with network info

atop -n

Launch with scheduling info

atop -s

Launch with various info (ppid, user, time)

atop -v

Launch with individual threads

atop -y

Once atop is running, press the following shortcut keys to sort processes:

• a – sort in order of most active resource.
• c – revert to sorting by CPU consumption (default).
• d – sort in order of disk activity.
• m – sort in order of memory usage
• n – sort in order of network activity

Guide to reading atop reports/logs

By default, after install, the atop daemon writes snapshots to a compressed log file (eg. /var/log/atop/atop_20140813). These log files can be read using:

atop -r /full/path/to/atop/log/file

Once you open a log file (e.g., atop -r /var/log/atop/atop_20140813), use t to go forward in 10-minute intervals and T to go back. You can analyze specific times by pressing b then entering the time. The above shortcut keys also work in this mode… a, c, d, m,n.

You can use shortcuts with atopsar. For example, using the flag “-c 30 5” with atopsar will generate a report for current CPU utilization for 5 minutes (ten times with intervals of 30 seconds):

atopsar -c 30 5

Using the flag -A with return all available reports.

atopsar -A

But you can limit this to a specific time window using beginning “-b” and end “-e” flags:

atopsar -A -b 11:00 -e 11:15

As you can see, it’s easy to use atop for Linux server performance analysis effectively.

Other popular command-line tools for Linux server performance analysis:

top, htop, nmon, net-tools, iptraf, collectl, glances, iostat and vmstat.