[Mageia-dev] ANNOUNCE: The /usr move cometh! <---- Instructions

Tue Sep 25 15:19:07 CEST 2012

'Twas brillig, and Thierry Vignaud at 25/09/12 11:07 did gyre and gimble:
+> On 9 September 2012 20:42, Colin Guthrie <mageia at colin.guthr.ie> wrote:
+>>> Those cannot be done anymore.
+>>> Now updating rpm in order to be able to sole the unifiedsystemdir depends
+>>> pulls filesystem...
+>>> Classic egg & chicken issue...
+>>
+>> Yes, this has been a problem for a while now in Cauldron. But not many
+>> users are asking this question these days, so the likely path now is
+>> from mga2 -> cauldron which is probably where the effort should be focused.
+> 
+> BTW I tested live upgrade from FC17 to FC18.
+> It works smoothly if you don't have third party packages.
+> in FC there's no need for a special boot, everything is hanled by filesystem
+> package's pre/post scripts:
+> 
+> $ rpm -q --scripts filesystem -v
+> pretrans scriptlet (using <lua>):
+> --#
+> --# If we are running in pretrans in a fresh root, there is no /usr
+> and symlinks.
+> --# We cannot be sure, to be the very first rpm in the transaction list,
+> --# so, let's create the toplevel symlinks here and the directories
+> they point to.
+> --# When our rpm is unpacked by cpio, it will set all permissions and
+> modes later.
+> --#
+> 
+> if posix.stat("/usr") == nil then
+>     posix.mkdir("/usr")
+> end
+> 
+> for i,dir in ipairs({"/lib", "/lib64", "/sbin", "/bin"}) do
+>     if posix.stat("/usr"..dir) == nil then
+>         posix.mkdir("/usr"..dir)
+>         if posix.stat(dir, "mode") == nil then
+>             posix.symlink("usr"..dir, dir)
+>         end
+>     end
+> end
+> 
+> return 0
+> postinstall scriptlet (using <lua>):
+> posix.symlink("../run", "/var/run")
+> posix.symlink("../run/lock", "/var/lock")
+
+We have pretty much the same script in our package if you look, but this
+does not process the move transition itself (i.e. there is nothing to
+move content from /bin to /usr/bin before rmdir'ing the dir and
+replacing it with a symlink).
+
+What this script achieves is to ensure that the filesystem layout is
+correct when installing the very first packages e.g. in a chroot. This
+is needed because some packages (not filesystem.rpm) may package a file
+/bin/foo. rpm does not guarentee ordering of the package installation
+transaction so if we install the foo package (which will trigger the
+installation of filesystem) we cannot guarentee that filesystem will be
+installed before foo and thus we need to prevent the creation of the
+/bin dir that would happen if foo was installed first.
+
+The comments in the script explain this pretty clearly.
+
+
+Regarding what does the actual move of files, I cannot say but if it
+happens automatically on a yum upgrade I'd certainly be interested to
+know how it's done without breaking things... Also I'm surprised that
+rpm let you do the upgrade as fedora have the same checks on their
+filesystem rpm as we do (i.e. it refuses to install if the /bin +
+friends are NOT symlinks)... so I'd be interested to know how this is
+done...
+
+Col
+
+
+
+-- 
+
+Colin Guthrie
+colin(at)mageia.org
+http://colin.guthr.ie/
+
+Day Job:
+  Tribalogic Limited http://www.tribalogic.net/
+Open Source:
+  Mageia Contributor http://www.mageia.org/
+  PulseAudio Hacker http://www.pulseaudio.org/
+  Trac Hacker http://trac.edgewall.org/
+