user.texinfo: Update apt-add-repository command line.

Explain how package and system upgrades are intended to work.

diff --git a/doc/user-manual/user.texinfo b/doc/user-manual/user.texinfo
index dde13630023058ae0a3c91d492c35e5b5dcb36c5..a5eee7dfa699694c0f72e5910115d056c947f2ce 100644 (file)
--- a/doc/user-manual/user.texinfo
+++ b/doc/user-manual/user.texinfo
@@ -4040,11 +4040,11 @@ sudo apt-key add ~/Downloads/mhb-key.gpg
 @end example
 
 Next add the repository to your list of package sources.
-On Ubuntu 17.04 (Zesty Zapus) you would use this command:
+On Ubuntu 17.10 (Artful Aardvark) you would use this command:
 
 @example
-sudo add-apt-repository \
-        -s "deb http://birchwood-abbey.net/ubuntu/ birchwood zesty"
+sudo add-apt-repository -s \
+    "deb http://birchwood-abbey.net/~puck/ubuntu/17.10/ birchwood main"
 @end example
 
 or by editing files in @file{/etc/apt/}.
@@ -4063,8 +4063,21 @@ sudo apt-get update
 sudo apt-get install mit-scheme-pucked-x11-screen
 @end example
 
-You can also download the package files and install them by hand.  Links to
-the available package files are listed on the project home page.
+Note that the Ubuntu version number is part of the source URL.  This
+allows new versions of Scheme and its plugins to be provided for old
+versions of Ubuntu.  (Normally you would upgrade to new versions of
+Ubuntu to get new versions of Scheme.)  However this means there may
+be @emph{three} packages named @code{mit-scheme-pucked} with the
+@emph{same} version, each compiled for Ubuntu 16.04, 17.10 or 18.04.
+
+When you upgrade to a new version of Ubuntu you should first remove
+the @code{mit-scheme-pucked} package (and all of its plugins), then
+re-install them after changing the source URL (e.g. to
+@url{http://birchwood-abbey.net/~puck/ubuntu/18.04/}).
+
+You can also download the package files and install them by hand.
+Links to the available package files are listed on the project home
+page.
 
 @example
 @uref{http://birchwood-abbey.net/~puck/Scheme/}
@@ -4122,6 +4135,10 @@ sudo dpkg --install ${P}-x11_0.2.1-1_amd64.deb
 sudo dpkg --install ${P}-x11-screen_0.2.1-1_amd64.deb
 @end verbatim
 
+As mentioned above, when you upgrade to a new version of Ubuntu you
+should first remove the @code{mit-scheme-pucked} package (and all of
+its plugins), then re-install them after changing the source URL.
+
 @node Unix Installation
 @section Unix Installation