Last Sync: 2022-08-28 11:00:04

Linux/Monitoring_processes_and_resources.md

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 categories:
   - Linux
-tags: [journal, systemd, sytems-programming]
+tags: [sytems-programming]
 ---
+
+# Monitoring processes and resources
+
+## Processor time and memory usage: `top`, `htop` etc
+
+We can use [ps](/Programming_Languages/Shell_Scripting/Processes.md) to list the currently running processes but it does not provide much information about the resource metrics or how the process changes over time. We can use `top` to get more information.
+
+`top` provides an interactive interface for the information that `ps` displays. It updates in real time and shows the most active processes based on the CPU time that they are utilising. You can also order by memory usage.
+
+_Here I have pressed `u` to show only the processes associated with my user:_
+
+![](/img/htop.png)
+
+### Main commands
+
+| Command | Action                          |
+| ------- | ------------------------------- |
+| -u      | Show processes by selected user |
+| M       | Sort by memory usage            |
+| P       | Sort by cumulative CPU usage    |
+| ?       | View key and explanation        |
+
+## Files being used by active processes: `lsof`
+
+`lsof` stands for _list open files_. It lists opened files and the processes using them. Without modifiers it outputs a huge amount of data. The best way to use it is to execute it against a specific PID. For example the below output gives me some useful info about which files VS Code is using:
+
+![](/img/lsof.png)
+
+## System calls: `strace`
+
+A system call is when a process requests a service from the [kernel](/Operating_Systems/The_Kernel.md), for instance an I/O operation to memory. We can trace these system calls with `strace`.