sudo pmset -a disablesleep 1

2 min read Original article ↗

TIL:

$ sudo pmset -a disablesleep 1

Keeps your MacBook running even when you close the screen. So you can keep that process running while you migrate from the coffee shop to the office. Or the office to the airport.

Embarrased to say the number of times I've kept the lid of my computer precariously cracked open in my backpack over the years.

Seemingly undocumented. I had heard about $ caffeinate -dimsu but that doesn't seem to work anymore, even though it's man page looks promising: 

$ man caffeinate

SYNOPSIS
     caffeinate [-disu] [-t timeout] [-w pid] [utility arguments...]

DESCRIPTION
     caffeinate creates assertions to alter system sleep behavior.  If no assertion flags are specified, caffeinate creates an assertion to
     prevent idle sleep.  If a utility is specified, caffeinate creates the assertions on the utility's behalf, and those assertions will
     persist for the duration of the utility's execution. Otherwise, caffeinate creates the assertions directly, and those assertions will
     persist until caffeinate exits.

     Available options:

     -d      Create an assertion to prevent the display from sleeping.

     -i      Create an assertion to prevent the system from idle sleeping.

     -m      Create an assertion to prevent the disk from idle sleeping.

     -s      Create an assertion to prevent the system from sleeping. This assertion is valid only when system is running on AC power.

     -u      Create an assertion to declare that user is active. If the display is off, this option turns the display on and prevents the
             display from going into idle sleep. If a timeout is not specified with '-t' option, then this assertion is taken with a default
             of 5 second timeout.

     -t      Specifies the timeout value in seconds for which this assertion has to be valid. The assertion is dropped after the specified
             timeout. Timeout value is not used when an utility is invoked with this command.

     -w      Waits for the process with the specified pid to exit. Once the the process exits, the assertion is also released.  This option
             is ignored when used with utility option.

EXAMPLE
     caffeinate -i make
        caffeinate forks a process, execs "make" in it, and holds an assertion that prevents idle sleep as long as that process is running.

SEE ALSO
     pmset(1)

LOCATION
     /usr/bin/caffeinate

Darwin                                                         November 9, 2012                                                        Darwin

Of course, don't forget to turn the flag back off so your computer can sleep again. 

$ sudo pmset -a disablesleep 0

Thanks Isaac for the tip.