On Sun, Jun 03, 2018 at 05:07:46AM +0000, Eitan Adler wrote: > > New Revision: 334552 > > URL: https://svnweb.freebsd.org/changeset/base/334552 > > > > Log: > > top(1): remove chdir to / > > > > While this came out of a conversation in IRC, it turn out that some > > people don't like it. Since this was a courtesy feature, just remove > it. >
At first I thought you were nuts to remove it, since I thought this was a wise change. However, I've changed my mind. I've done some research behind this practice. A long time ago, it used to be critical to the operation of the system: long running processes could prevent a reboot. The 7th Edithion and earlier didn't even have a reboot system call[*]. In System III and original System V based systems, you even had to cd / before doing a shutdown. Otherwise the umounts of all the filesystems except / would fail. There were no forcing provisions in the code at that time. Long running processes would cd to / to avoid problems with people needing to unmount a filesystem and secondarily to ensure that the umounts would work if there were issues with the process dying at reboot time. Somewhere around SysV r3 or so, these restrictions were lessoned and by the time Solaris forked from SysV r4, they were mostly gone. BSD kernels appear to have had similar issues, but they were fixed (or became moot) very early on (maybe between 2.8 and 2.9, google isn't as helpful as I'd had hoped here, and I didn't want to sink a ton of time reading code on TUHS). Fast forward to today, and they are unneeded. There's no issue with reboot. There can be minor issues with umounting filesystems. fstat(1) can be used, though it's a bit cumbersome, to find stray references. Warner [*] OK, a system call number was reserved for reboot, but it wasn't implemented. _______________________________________________ svn-src-all@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/svn-src-all To unsubscribe, send any mail to "svn-src-all-unsubscr...@freebsd.org"
