How to get percentage of processor use with bash?
Processor use or utilization is a measurement over time. One way to measure utilization in % is by computation over two successive reads of /proc/stat. A simple common bash script to compute the percentage is:
#!/bin/bash
# Read /proc/stat file (for first datapoint)
read cpu user nice system idle iowait irq softirq steal guest< /proc/stat
# compute active and total utilizations
cpu_active_prev=$((user+system+nice+softirq+steal))
cpu_total_prev=$((user+system+nice+softirq+steal+idle+iowait))
usleep 50000
# Read /proc/stat file (for second datapoint)
read cpu user nice system idle iowait irq softirq steal guest< /proc/stat
# compute active and total utilizations
cpu_active_cur=$((user+system+nice+softirq+steal))
cpu_total_cur=$((user+system+nice+softirq+steal+idle+iowait))
# compute CPU utilization (%)
cpu_util=$((100*( cpu_active_cur-cpu_active_prev ) / (cpu_total_cur-cpu_total_prev) ))
printf " Current CPU Utilization : %s\n" "$cpu_util"
exit 0
use/output:
$ bash procstat-cpu.sh
Current CPU Utilization : 10
output over 5 iterations:
$ ( declare -i cnt=0; while [ "$cnt" -lt 5 ]; do bash procstat-cpu.sh; ((cnt++)); done )
Current CPU Utilization : 20
Current CPU Utilization : 18
Current CPU Utilization : 18
Current CPU Utilization : 18
Current CPU Utilization : 18
top -bn1 | sed -n '/Cpu/p'
gives the following line
Cpu(s): 15.4%us, 5.3%sy, 0.0%ni, 78.6%id, 0.5%wa, 0.0%hi, 0.1%si, 0.0%st
You can pull any CPU field with the following will take the user CPU (us)
top -bn1 | sed -n '/Cpu/p' | awk '{print $2}' | sed 's/..,//'
Output:
15.4%
If you want another field like system CPU (sy) you can change the awk field from $2,
top -bn1 | sed -n '/Cpu/p' | awk '{print $3}' | sed 's/..,//'
Output:
5.3%
If you want other CPU:
us: user CPU used by user processes
sy: system CPU used by system/kernel processes
ni: nice CPU used by processes that were reniced
id: idle CPU not used
wa: io wait Essentially idle CPU waiting on IO devices
hi: hardware irq CPU used to service hardware IRQs
si: software irq CPU used to service soft IRQs
st: steal time CPU time which the hypervisor dedicated (or ‘stole’) for other guests in the system.
To get usage percent total since bringing the system up:
awk '/cpu /{print 100*($2+$4)/($2+$4+$5)}' /proc/stat
To get the usage percentage over the last second:
awk -v a="$(awk '/cpu /{print $2+$4,$2+$4+$5}' /proc/stat; sleep 1)" '/cpu /{split(a,b," "); print 100*($2+$4-b[1])/($2+$4+$5-b[2])}' /proc/stat
Explanation
From man 5 proc, the meaning of the first four numbers on the cpu line in /proc/stat is given by:
cpu 3357 0 4313 1362393
The amount of time, measured in units of USER_HZ (1/100ths of a second on most architectures, use sysconf(_SC_CLK_TCK) to obtain the right value), that the system spent in user mode, user mode with low priority (nice), system mode, and the idle task, respectively. The last value should be USER_HZ times the second entry in the uptime pseudo-file.
The get the CPU usage, we add the user and system times and divide by the total of user, system, and idle time.
Let's look again at the calculation for total CPU usage since system up:
awk '/cpu /{print 100*($2+$4)/($2+$4+$5)}' /proc/stat
By requiring that the line match cpu, we get system totals. The second column is user time, the fourth is system time, and the fifth is idle time. The ratio is multiplied by 100 to get a percentage.
Now, let's consider the recent CPU usage:
awk -v a="$(awk '/cpu /{print $2+$4,$2+$4+$5}' /proc/stat; sleep 1)" '/cpu /{split(a,b," "); print 100*($2+$4-b[1])/($2+$4+$5-b[2])}' /proc/stat
This reads /proc/cpu twice, a second apart. The first time, the CPU user + system, and user+system+idle times are saved in the variable a. sleep is called to delay for a second. Then, /proc/cpu is read a second time. Tne old user+system total is subtracted from the new total and divided by the change in the total of all times. The result is multiplied by 100 to convert it to percent and printed.