Power Down System (PWRDWNSYS)
The Power Down System (PWRDWNSYS) command prepares the system for
ending and then starts the power-down sequence. All active
subsystems are notified that the system is being powered down; no
new jobs or routing steps can be started by any subsystem.
Use GO CMDPWR for other POWER commands.
enjoy life. it is not a dress rehearsal.
PWRDWNSYS will turn off your iSeries (i5 or AS/400) and to perform an IPL the command needs an additional parameter.
This will perform everything Phil says and restart your machine.
Both answers are assuming the system is actually on and he’s looking to reboot, rather than IPL’ing from an off state using the correct panel code and the power button.