> 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". P.
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
> 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. >The SunOS 4.1.2 man page for halt says NAME halt - stop the processor SYNOPSIS /usr/etc/halt [ -oqy ] DESCRIPTION halt writes out any information pending to the disks and then stops the processor. halt normally logs the system shutdown to the system log daemon, syslogd(8), and places a shutdown record in the login accounting file Ivar/admlwtmp. These actions are inhibited if the -0 or -q options are present. The BSD 4.3 (that ran on VAXen) man pages say largely similar things: https://www.freebsd.org/cgi/man.cgi?query=halt&apropos=0&sektion=0&manpath=4.3BSD+Reno&arch=default&format=html Everything is somewhere on the net :-) P.