time - run programs and summarize system resource usage

syntax

$ time [options] [command]

Real: This is the actual time taken by the processor of the computer to execute the command from pressing the button to complete the command.
User: CPU time that is taken by the user mode.
SYS: This is the time taken by the system or the Kernel to execute the command.

To calculate execution time of commands

$ time sleep 5

$ time free -h

$ time df -Th

$ time ping google.com

To display the time in portable POSIX format

$ time -p sleep 5

$ time -p free -h

$ time -p df -Th

$ time -p ping google.com

To calculate the update time 

$ time sudo apt update 

To save the time command output in the text file

$ /usr/bin/time -o sleep_output.txt sleep 5

$ /usr/bin/time -o df_output.txt df -Th

To get detailed summary of the executed time

$ /usr/bin/time -v sleep 5

$ /usr/bin/time -v df -Th

$ /usr/bin/time -v free -h

regards,

T.Dhanasekar