netdata/health/guides/load/load_average_5.md

Understand the alert

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

The alert gets raised into warning if the metric is 4 times the expected value and cleared if the value is 3.5 times the expected value.

For further information on how our alerts are calculated, please have a look at our Documentation.

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.

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

Troubleshoot the alert

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

First you need to check if you are running on a CPU load or an I/O load problem.

1. 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.

1. List your currently running processes using the ps command:

The grep command will fetch the processes that their state code starts either with R (running or runnable (on run queue)) or D(uninterruptible sleep (usually IO)).

1. 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.

• 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.