3. Monitoring your server

Understanding your system

So now we want to be able to navigate, operate and monitor our system. To do this, most servers have a relatively homogenous system: systemd!

systemd is a software suite that provides an array of system components for Linux operating systems. The main aim is to unify service configuration and behavior across Linux distributions.

systemctl is the command-line tool that manages the systemd system and service manager in Linux.

• How to work with systemd units, etc

  • Many modern Linux distros go with systemd — it can handle services for you in a convenient manner

  • It comes with systemctl, along with a lot of other things — DNS caching resolvers, time sync, a bootloader, etc, But we'll want to focus on systemctl

  • Start/stop/restart services: systemctl start unit.service, etc

  • Check service status: systemctl status unit.service

journalctl is a utility for querying and displaying logs from journald, systemd’s logging service.

To see live logs:

journalctl -f

To see the first 20 lines

journalctl -n 20

To check a specific service:

journalctl -u sshd

To get all logs from last boot

journalctl -b

To filter by time (last 15 minutes for example)

journalctl --since "15 minutes ago"

Monitoring with top

Aside from reading warnings, and making sure our services are running, we often times also want to make sure our system as a whole is running as expected. This is where top and htop come into play

What is top?

• top command is used to show the Linux processes. It provides a dynamic real-time view of the running system.

• Think of it as a super powerful task manager for Linux.

Basic Usage

• Just type top to start the program.

• Pressing q will simply exit the command mode.

• Pressing h will show you the help menu.

What does everything mean?

• PID: Shows task’s unique process id.

• PR: The process’s priority. The lower the number, the higher the priority.

• VIRT: Total virtual memory used by the task.

• USER: User name of owner of task.

• %CPU: Represents the CPU usage.

• TIME+: CPU Time, the same as ‘TIME’, but reflecting more granularity through hundredths of a second.

• SHR: Represents the Shared Memory size (kb) used by a task.

• NI: Represents a Nice Value of task. A Negative nice value implies higher priority, and positive Nice value means lower priority.

• %MEM: Shows the Memory usage of task.

• RES: How much physical RAM the process is using, measured in kilobytes.

• COMMAND: The name of the command that started the process.

top cheatsheet

https://gist.github.com/ericandrewlewis/4983670c508b2f6b181703df43438c3gist.github.com

Some exercises!

• Try running top and see what you can find out about your system!

• What are the top 5 processes using the most CPU?

• What would I press if I want to kill the processes using the most memory?

• I want to see what processes start running when I start my computer. How would I do that?

Solution

• What are the top 5 processes using the most CPU?

  • top -> Shift + P

• What would I press if I want to kill the processes using the most memory?

  • top -> Shift + M -> k

• I want to see what processes start running when I start my computer.

  • top -> f -> PID -> s -> q -> Shift + R