Prerequisites

To follow along with this guide, you will need access to a computer running a Linux-based operating system. This can either be a virtual private server which you’ve connected to with SSH or your local machine. Note that this tutorial was validated using a Linux server running Ubuntu 20.04, but the examples given should work on a computer running any version of any Linux distribution.

If you plan to use a remote server to follow this guide, we encourage you to first complete our Initial Server Setup guide. Doing so will set you up with a secure server environment — including a non-root user with sudo privileges and a firewall configured with UFW — which you can use to build your Linux skills

Step 1 – How To View Running Processes in Linux

You can see all of the processes running on your server by using the top command:

The remainder of the displayed output shows the running processes and their usage statistics. By default, top automatically sorts these by CPU usage, so you can see the busiest processes first. top will continue running in your shell until you stop it using the standard key combination of Ctrl+C to exit a running process. This sends a kill signal, instructing the process to stop gracefully if it is able to

An improved version of top, called htop, is available in most package repositories. On Ubuntu 20.04, you can install it with apt:

Here are some keyboard shortcuts that will help you use htop more effectively:

There are many other options that you can access through help or setup. These should be your first stops in exploring htop’s functionality. In the next step, you’ll learn how to monitor your network bandwidth.

Step 2 – How To Monitor Your Network Bandwidth

If your network connection seems overutilized and you are unsure which application is the culprit, a program called nethogs is a good choice for finding out.

On Ubuntu, you can install nethogs with the following command:

After that, the nethogs command will be available:

nethogs associates each application with its network traffic.

There are only a few commands that you can use to control nethogs:

On Ubuntu, you can install iptraf-ng with the following command:

iptraf-ng needs to be run with root privileges, so you should precede it with sudo:

You’ll be presented with a menu that uses a popular command line interface framework called ncurses.

For example, to get an overview of all network traffic, you can select the first menu and then “All interfaces”. It will give you a screen that looks like this:

If you would like to have those IP addresses resolved into domains, you can enable reverse DNS lookup by exiting the traffic screen, selecting Configure and then toggling on Reverse DNS lookups.

With both of these options enabled, the display may look like this:

netstat is installed by default on most modern systems, but you can install it yourself by downloading it from your server’s default package repositories. On most Linux systems, including Ubuntu, the package containing netstat is net-tools:

By default, the netstat command on its own prints a list of open sockets:

If you add an -a option, it will list all ports, listening and non-listening:

If you’d like to filter to see only TCP or UDP connections, use the -t or -u flags respectively:

See statistics by passing the “-s” flag:

In the next step, you’ll learn some useful ways of monitoring your disk usage.

Step 3 – How To Monitor Your Memory Usage

You can check the current memory usage on your system by using the free command

When used without options, the output looks like this:

To display in a more readable format, you can pass the -m option to display the output in megabytes:

The Mem line includes the memory used for buffering and caching, which is freed up as soon as needed for other purposes. Swap is memory that has been written to a swapfile on disk in order to conserve active memory.

Finally, the vmstat command can output various information about your system, including memory, swap, disk io, and cpu information.

You can use the command to get another view into memory usage:

You can see this in megabytes by specifying units with the -S flag:

To get some general statistics about memory usage, type:

This will give you details about what kind of information is stored in the cache.

Conclusion