Intro To 'sleep' Command In Linux

2023-05-23 - By Robert Elder

     I use the 'sleep' command to delay for a specified amount of time:

sleep 123

     If I run the 'sleep' command with a value of 1, it will do absolutely nothing for one second and then return control to the prompt:

sleep 1

     Many versions of the 'sleep' command will allow you to specify a time as a floating point number as well as an integer:

sleep 0.3
sleep 1.3

Sleep Using Units - Seconds, Minutes, Hours, Days

     Some versions of the 'sleep' command will allow you to specify a suffix after the number to control whether the 'sleep' time indicates seconds, minutes, hours, or days:

sleep 1.3m

     You can consult the 'info' pages of the sleep command for a list of suffixes:

info sleep

25.1 ‘sleep’: Delay for a specified time
========================================

‘sleep’ pauses for an amount of time specified by the sum of the values
of the command line arguments.  Synopsis:

     sleep NUMBER[smhd]...

   Each argument is a number followed by an optional unit; the default
is seconds.  The units are:

‘s’
     seconds
‘m’
     minutes
‘h’
     hours
‘d’
     days

Using 'sleep' To Lower CPU Usage In Busy Loops

     The 'sleep' command is useful for scripting because it lets you delay program execution without wasting CPU usage inside of a busy loop.  If I run this command in a busy loop:

for i in {1..10000000}; do :; done

     it will also cause a delay just like the 'sleep' command does, but it also consumes 100% of the CPU:

     The 'sleep' command allows for delays without wasting CPU by taking advantage of blocking features within the operating system scheduler.  If I run this command instead:

while true; do :; sleep 1; done

     you can see that the CPU usage is now much lower:

     And that's why the 'sleep' command is my favourite Linux command.

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