StackWise - IOS upgrade switch reboot sequence
In a StackWise configuration of multiple switches, when upgrading the IOS of the stack, the sequence of the rebooting of the switches typically takes place simultaneously for all switches.
For Catalyst switches in the 9K series, the autoboot feature is enabled, which causes all the switches to automatically reboot when the IOS is upgraded.
Links
https://forum.networklessons.com/t/cisco-stackwise/1160/121?u=lagapidis