Linux Uptime Command: View System Uptime and Load

The uptime command in Linux shows how long the system has been running, the number of logged-in users, and the CPU load.

The most common options are:

• -p        Shows how long the system has been up in a "nice" format
• -s        Shows how long the system has been up in YEAR-MONTH-DAY HOUR:MINUTE:SECOND format

The CPU load averages shown by the uptime command are calculated as the average of processes running or waiting for the CPU. These averages are not normalized by the number of CPUs.

It is very important to remember that uptime shows the CPU load average for the last 1 minute, the last 5 minutes, and the last 15 minutes, in that order.

If the CPU load is greater than 1, and the system has only one CPU, it means the CPU usage is beyond capacity, therefore there is a large wait for CPU by the processes.

But to draw more accurate conclusions, it depends on how long the CPU average has been above 1. If there was a CPU usage spike in the last minute, but the load averages for the 5 and 15 minute periods are low, it is not an indication that there is a need to replace the CPU. But if the averages are also high at 5 and 15 minutes, it means the processing capacity may be poorly planned in relation to the system load.

It is also important to know that these averages are not normalized by the number of processors. A load number of 1 on a system with 4 processors means the CPUs are idle 75% of the time. This way, you can understand that to overload a system with 4 CPUs, the average load needs to be greater than 4.

See in this example that there is CPU to spare:

$ uptime 20:35:37 up 31 days,  9:41,  1 user,  load average: 0,02, 0,02, 0,00

The -p option shows how long the system has been up in a day-counting style:

$ uptime -pup 4 weeks, 3 days, 9 hours, 45 minutes

And the -s option shows how long the system has been up in date format:

$ uptime -s2019-08-15 10:53:45

The number of CPUs in a system can be viewed in the /proc/cpuinfo file, with the "model name" parameter:

$ grep -c 'model name' /proc/cpuinfo1

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