# Monitoring ### 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: ```bash journalctl -f ``` To see the first 20 lines ```bash journalctl -n 20 ``` To check a specific service: ```bash journalctl -u sshd ``` To get all logs from last boot ```bash journalctl -b ``` To filter by time (last 15 minutes for example) ```bash 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 {% embed url="" %} #### 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`
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