Hi, On 2021-07-29 7:35 a.m., Thomas Schmitt wrote: > Hi, > > tomas@tuxteam.de wrote: >>> While I've read about issuing sync *twice* with the explanation >>> that sysadmins are a supersticious bunch > > Polyna-Maude Racicot-Summerside wrote: >> I'm really asking why do it 3 time. >> In case it came back to the prompt *before* finishing to do it's job ? > > I dimly remember that it was part of the shutdown procedure of one of > the earliest Unix machines which i met. IBM RT, Apollo DN3000, microVAX ... ? > The shutdown spell was something like > Sorry, I'm too young for IBM RT, HP Apollo DN3000 or any type of VAX (except in a emulator). > sync ; sync ; halt > > Googling "sync halt" leads me to an interesting theory at > https://bsdimp.blogspot.com/2020/07/when-unix-learned-to-reboot2.html > > According to section "That sync; sync; sync Thing..." two bugs of early > systems' sync existed (one explored by the blog's author, one as rumor): > > 1: The sync system call returned without waiting. > Workaround: > Keep the human operator busy while the machine is still not done with > flushing buffers. E.g. prescribe to type three lines of "sync" before > typing "halt". > > 2: Only the first sync call returned early, whereas the second sync > properly blocked until flushing was done. > That seems to be the origin of my memory. > > Thanks for this bit of history :) > Have a nice day :) > > Thomas > -- Polyna-Maude R.-Summerside -Be smart, Be wise, Support opensource development
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