High System Load

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General Information

Troubleshooting high system load.

Checklist

The following tools are useful when troubleshooting system load.

Typically built in

Need to install (if using a minimal install base)

Base Repo

yum -y install iotop sysstat

Know how many processors you have. This is essential to determine if load is high.
1. ```
grep -c processor /proc/cpuinfo
```
2. %Load (decimal) = (Load Average / Number Processors)
3. Example: Number of processors = 2, load average seen = 1.50
4. 1.50 / 2 = 0.75 or 75% load on the processors
Check load averages
1. Uptime shows the load average for the last 1, 5, and 15 minutes. If it is too high or trending up, time to investigate further.
2. ```
uptime
```
What kind of load
1. Use vmstat to determine what kind of system load. “vmstat 1” prints stats every 1 second.
  1. ```
  vmstat 1
```
2. Important columns to take note of:
  1. CPU: “wa” ⇒ Time spent waiting for I/O. If high, something is probably heavily utilizing disk.
  2. CPU: “id” ⇒ CPU time spent idle. If close to 0, CPU is used heavily.
  3. CPU: “sy” ⇒ CPU time spent running system/kernel processes. Mail and firewalls are common causes of high system use.
  4. CPU: “us” ⇒ CPU time spent running user processes. If high, investigate with top.
  5. SWAP: “si” ⇒ Memory swapped in from disk each second.
  6. SWAP: “so” ⇒ Memory swapped to disk each second.
    1. If either are high, memory is most likely also very low.
3. Further investigate either high CPU use or Disk I/O

top

iostat
iotop

Troubleshooting Tools