How do I calculate CPU usage percentage? – Linux Tips And Tricks

Learn how to calculate CPU usage percentage in Linux.

The /proc/stat file keeps track of a variety of different statistics about the system since it was last restarted.

grep ‘cpu ‘ /proc/stat
OUTPUT
cpu 6992 1362 21245 11173867 914 0 2498 0 0 0

The number shown next to the cpu is the amount of time, measured in jiffies (1/100ths of a second on most architectures, use sysconf(_SC_CLK_TCK) to obtain the right value), that the system (“cpu” line) or the specific CPU (“cpuN” line) spent in various states:

The very first “cpu” line aggregates the numbers in all of the other “cpuN” lines.
From left to right.
user: normal processes executing in user mode
nice: same as user processes but executing in as a low priority
system: processes executing in kernel mode
idle: twiddling thumbs
iowait: waiting for I/O to complete
irq: servicing interrupts (hardware irq)
softirq: servicing softirqs

The “intr” line gives counts of interrupts serviced since boot time.
The “ctxt” line gives the total number of context switches across all CPUs.
The “btime” line gives the time at which the system booted, in seconds since the Unix epoch.
The “processes” line gives the number of processes and threads created, which includes (but is not limited to) those created by calls to the fork() and clone() system calls.
The “procs_running” line gives the number of processes currently running on CPUs.
The “procs_blocked” line gives the number of processes currently blocked, waiting for I/O to complete.
The “softirq” is the software version of the hardware interrupts.

To calculate the percentage of cpu used by system processes, use this command.
grep ‘cpu ‘ /proc/stat | awk ‘{usage=($4)*100/($2+$3+$4+$5+$6+$7+$8+$9+$10+$11)} END {print usage “%”}’

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