Server loadEdit

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Server load or simply load is a measure of resource usage commonly used to indicate the intensity of demands upon an Internet server. The number is an indication of the number of waiting processes waiting to get a slice of the processor time at the moment the load measurement was taken. A load average close to 0.0 indicates that the machine is only very lightly loaded and (almost) no processes have to wait when they want a slice of processor time. Ideally load averages should be kept down near 0, 1 or 2. As the load average gets higher system responsiveness is reduced. Load averages over 10 are very high, and averages over 20 are extremely high.

Load can also be measured on desktop machines running operating systems such as Mac OS X. For example, open up a Terminal window and use the uptime tool to view the load averages over the last minute, 5 minutes and 15 minutes:

$ uptime
18:05  up  5:49, 4 users, load averages: 0,34 0,40 0,42

In this example, the load average over the last minute was 0.34 (appearing as 0,34 in this case because in the Spanish locale the comma is used as a decimal separator), load average during the last five minutes was 0.40, and load average over the last fifteen minutes was 0.42.

For comparison, here is some output from a server running Red Hat Enterprise Linux:

11:10:41  up 233 days,  2:00,  2 users,  load average: 0.03, 0.06, 0.59

Load averages can also be monitored in realtime using top or w (in Mac OS X as well) or tload (only in Red Hat Enterprise Linux).

Slightly more sophisticated load average reports can be obtained using a command like the following:

sar -Hqt         | \
 cut -f3,6 -d';' | \
 tr  ' ;' ',,'   | \
 cut -f2,3 -d ','|
 mail -s "Today's load levels" user@example.com

This does the following:

  • Get a list of load averages for the day at 10 minute intervals
  • Cut all but the 3rd and 6th columns of the input (columns delimited by a semicolon)
  • Replace spaces and semicolons with commas (useful for importing into a database or spreadsheet)
  • Further cut the input, leaving only the 2nd and 3rd columns (now delimited by a comma)
  • Mail the output to the specified email address