WIP

src/Propellor/Property/OS.hs

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+module Propellor.Property.OS (
+	cleanInstallOnce,
+	Confirmation
+	confirm,
+	fixupNetworkAddresses,
+	fixupRootSsh,
+	oldOSRemoved,
+) where
+
+import Propellor
+import qualified Propellor.Property.Chroot as Chroot
+import qualified Propellor.Property.Debootstrap as Debootstrap
+
+-- | Replaces whatever OS was installed before with a clean installation
+-- of the OS that the Host is configured to have.
+--
+-- This can replace one Linux distribution with different one.
+-- But, it can also fail and leave the system in an unbootable state.
+--
+-- This property only runs once. The cleanly installed system will have
+-- a file /etc/propellor-cleaninstall, which indicates it was cleanly
+-- installed.
+--
+-- You will typically want to run some more properties after the clean
+-- install, to bootstrap from the cleanly installed system to a fully
+-- working system. For example:
+--
+-- > & os (System (Debian Unstable) "amd64")
+-- > & cleanInstall (confirm "com.example.foo") (BackupOldOS <> UseOldKernel)
+-- >    `onChange` propertyList "fixing up after clean install"
+-- >        [ fixupNetworkInterfaces
+-- >        , fixupRootSsh
+-- >        -- , installDistroKernel
+-- >        -- , installGrub
+-- >        ]
+-- > & Apt.installed ["ssh"]
+-- > -- rest of system properties here
+cleanInstallOnce :: Confirmation -> Exceptions -> Property
+cleanInstallOnce c = check (not <$> doesFileExist flagfile) $
+	Property "OS cleanly installed" $ do
+		confirm c
+		error "TODO"
+		-- debootstrap /new-os chroot; avoid running
+		--   propellor inside the chroot yet
+		-- unmount all mounts
+		-- move all directories to /old-os,
+		--   except for /boot and /lib/modules
+		-- move /new-os to /
+		-- touch /etc/propellor-cleaninstall
+		-- re-bootstrap propellor in /usr/local/propellor,
+		--   (using git repo bundle, privdata file, and possibly
+		--   git repo url, which all need to be arranged to
+		--   be present in /old-os's /usr/local/propellor)
+		-- return MadeChange
+  where
+	flagfile = "/etc/propellor-cleaninstall"
+
+-- | To confirm you really intend to apply a dangerous Property to a
+-- system, and have not copied and pasted it in by accident, you must
+-- provide as confirmation, the hostname of the system you intend
+-- to apply the Property to, written in the form form "com.example.somehost"
+newtype Confirmation = Confirmation String
+
+confirm :: String -> Confirmation
+confirm (Confirmation c) h
+	| h ==(intercalate "." $ reverse $ split "." c) = return ()
+	| otherwise = error "Bad confirmation of dangerous Property; see the documentation to fix this."
+
+-- | Sometimes you want an almost clean install, but with some exceptions.
+data Exceptions
+	= UseOldKernel -- ^ Leave /boot and /lib/modules from old OS, so the system can boot using them as before
+	| BackupOldOS -- ^ Back up old OS to /old-os, to avoid losing any important files
+	| NoExceptions
+	| CombinedExceptions Exceptions Exceptions
+
+instance Monoid Exceptions where
+	mempty = NoExceptions
+	mappend = CombinedExceptions
+
+-- /etc/network/interfaces is configured to bring up all interfaces that
+-- are currently up, using the same IP addresses.
+--
+-- This property only does anything if it comes after cleanInstall,
+-- in the same propellor run where cleanInstall has made a change.
+fixupNetworkInterfaces :: Property
+fixupNetworkInterfaces = undefined
+
+-- /root/.ssh/authorized_keys is copied from the old os
+fixupRootSsh :: Property
+fixupRootSsh = undefined
+
+-- Installs an appropriate kernel from the distribution.
+installDistroKernel :: Property
+installDistroKernel = undefined
+
+-- Installs grub to boot the system.
+installGrub :: Property
+installGrub = undefined
+
+-- Removes the old OS's backup from /old-os
+oldOSRemoved :: Property
+oldOSRemoved = check (doesDirectoryExist oldOsDir) $
+	Property "old OS backup removed" $ liftIO $ do
+		removeDirectoryRecursive oldOsDir
+		return MadeChange
+
+oldOsDir :: FilePath
+oldOsDir = "/old-os"