netdata/health/guides/load/load_average_1.md

Understand the alert

This alarm calculates the system load average (CPU and I/O demand) over the period of one minute. If you receive this alarm, it means that your system is overloaded.

What does "load average" mean?

The term system load average on a Linux machine, measures the number of threads that are currently working and those waiting to work (CPU, disk, uninterruptible locks). So simply stated: System load average measures the number of threads that aren't idle.

What does "overloaded" mean?

Let's look at a single core CPU system and think of its core count as car lanes on a bridge. A car represents a process in this example:

• On a 0.5 load average, the traffic on the bridge is fine, it is at 50% of its capacity.
• If the load average is at 1, then the bridge is full, and it is utilized 100%.
• If the load average gets to 2 (remember we are on a single core machine), it means that there is one car lane that is passing the bridge. However, there is another full car lane that waits to pass the bridge.

So this is how you can imagine CPU load, but keep in mind that load average counts also I/O demand, so there is an analogous example there.

Troubleshoot the alert

• Determine if the problem is CPU load or I/O load

To get a report about your system statistics, use vmstat (or vmstat 1, to set a delay between updates in seconds):

The procs column, shows:
r: The number of runnable processes (running or waiting for run time).
b: The number of processes blocked waiting for I/O to complete.

• Check per-process CPU/disk usage to find the top consumers

1. To see the processes that are the main CPU consumers, use the task manager program top like this:

   top -o +%CPU -i
   

2. Use iotop:
   iotop is a useful tool, similar to top, used to monitor Disk I/O usage, if you don't have it, then install it

   sudo iotop
   

3. Minimize the load by closing any unnecessary main consumer processes. We strongly advise you to double-check if the process you want to close is necessary.

Useful resources

1. UNIX Load Average Part 1: How It Works
   
2. UNIX Load Average Part 2: Not Your Average Average
   
3. Understanding Linux CPU Load
   
4. Linux Load Averages: Solving the Mystery
   
5. Understanding Linux Process States