To find out how long a Unix or Linux system has been running, we can use the uptime command. This command will show the current time, the length of time the system has been running, the number of users logged in, and the load average over the last 1, 5, and 15 minutes. For example:  $ uptime
21:52:06 up 3 days, 6:22, 2 users, load average: 0.00, 0.00, 0.00  In this example, the system has been running for 3 days and 6 hours (3 days, 6:22).  We can also use the who -b command to show the time that the system was last booted. For example:  $ who -b
system boot 2021-07-14 21:50 This will show the date and time that the system was last booted.  Keep in mind that these commands may not work on all systems, and the output may vary depending on the specific operating system and version.  A must-know for anyone heading into a Shell Scripting interview, this is one of the most frequently asked UNIX Shell Scripting interview questions.