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--- admin_grundlagen:verzeichnisbaum [2023/05/17 20:59]
ingo_wichmann
+++ admin_grundlagen:verzeichnisbaum [2023/05/17 21:02] (aktuell)
ingo_wichmann
@@ Zeile 8: / Zeile 8: @@
 [[admin_grundlagen:verzeichnisbaum_uebung|Verzeichnisbaum Übung]]
-(( Warum das alles komplizierter ist, als es sein müßte: http://lists.busybox.net/pipermail/busybox/2010-December/074114.html ))
+(( Warum das alles komplizierter ist, als es sein müsste: http://lists.busybox.net/pipermail/busybox/2010-December/074114.html
+von Rob Landley, 2010
+You know how Ken Thompson and Dennis Ritchie created Unix on a PDP-7 in 1969?
+Well around 1971 they upgraded to a PDP-11 with a pair of RK05 disk packs (1.5
+megabytes each) for storage.
+When the operating system grew too big to fit on the first RK05 disk pack (their
+root filesystem) they let it leak into the second one, which is where all the
+user home directories lived (which is why the mount was called /usr).  They
+replicated all the OS directories under there (/bin, /sbin, /lib, /tmp...) and
+wrote files to those new directories because their original disk was out of
+space.  When they got a third disk, they mounted it on /home and relocated all
+the user directories to there so the OS could consume all the space on both
+disks and grow to THREE WHOLE MEGABYTES (ooooh!).
+Of course they made rules about "when the system first boots, it has to come up
+enough to be able to mount the second disk on /usr, so don't put things like
+the mount command /usr/bin or we'll have a chicken and egg problem bringing
+the system up."  Fairly straightforward.  Also fairly specific to v6 unix of 35
+years ago.
+The /bin vs /usr/bin split (and all the others) is an artifact of this, a
+'s implementation detail that got carried forward for decades by
+bureaucrats who never question _why_ they're doing things.  It stopped making
+any sense before Linux was ever invented, for multiple reasons:
+) Early system bringup is the provice of initrd and initramfs, which deals
+with the "this file is needed before that file" issues.  We've already _got_ a
+temporary system that boots the main system.
+) shared libraries (introduced by the Berkeley guys) prevent you from
+independently upgrading the /lib and /usr/bin parts.  They two partitions have
+to _match_ or they won't work.  This wasn't the case in 1974, back then they
+had a certain level of independence because everything was statically linked.
+) Cheap retail hard drives passed the 100 megabyte mark around 1990, and
+partition resizing software showed up somewhere around there (partition magic
+.0 shipped in 1997).
+Of course once the split existed, some people made other rules to justify it.
+Root was for the OS stuff you got from upstream and /usr was for your site-
+local files.  Then / was for the stuff you got from AT&T and /usr was for the
+stuff that your distro like IBM AIX or Dec Ultrix or SGI Irix added to it, and
+/usr/local was for your specific installation's files.  Then somebody decided
+/usr/local wasn't a good place to install new packages, so let's add /opt!
+I'm still waiting for /opt/local to show up...
+Of course given 30 years to fester, this split made some interesting distro-
+specific rules show up and go away again, such as "/tmp is cleared between
+reboots but /usr/tmp isn't".  (Of course on Ubuntu /usr/tmp doesn't exist and
+on Gentoo /usr/tmp is a symlink to /var/tmp which now has the "not cleared
+between reboots" rule.  Yes all this predated tmpfs.  It has to do with read-
+only root filesystems, /usr is always going to be read only in that case and
+/var is where your writable space is, / is _mostly_ read only except for bits
+of /etc which they tried to move to /var but really symlinking /etc to
+/var/etc happens more often than not...)
+Standards bureaucracies like the Linux Foundation (which consumed the Free
+Standards Group in its' ever-growing accretion disk years ago) happily
+document and add to this sort of complexity without ever trying to understand
+why it was there in the first place.  'Ken and Dennis leaked their OS into the
+equivalent of home because an RK05 disk pack on the PDP-11 was too small" goes
+whoosh over their heads.
+))

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