On Sun, Jun 14, 2020 at 5:20 PM Pete Biggs <pete at biggs.org.uk> wrote: > > > fwiw, i've always used 'init 0' to shut down all sorts of unix/linux > > systems. > > In EL7/EL8, init is now a symlink as well because everything is > controlled by systemd. > > > On old school unix, and I think even early Linux, halt was an > > /immediate/ halt, as in catch fire. might as well hit the power switch. > > > Not quite. Shutdown is a timed thing so you can tell it to shutdown or > reboot at a certain time or after a certain delay and it can broadcast > messages to the users - it's useful on multi-user systems to be able to > warn users that the system is about to go down. Halt is an immediate > thing without any broadcast messages or delay but it does do the halt > cleanly. There is an option to halt to not sync the disks - this is > not a wise thing to do and is an emergency option - certainly the > original man pages for halt said something like "only do this if your > disks are on fire". I'm quite sure that in original Berkeley Unix, as on the VAX 11/780, halt was an immediate halt of the CPU without any process cleanup or file system umounting or anything. Early SunOS (pre-Solaris) was like this, too. -- -john r pierce recycling used bits in santa cruz