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| 2 | <!DOCTYPE note PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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| 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
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| 4 | <!ENTITY % general-entities SYSTEM "../general.ent">
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| 5 | %general-entities;
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| 6 | ]>
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| 7 |
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| 8 | <!-- $LastChangedBy$
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| 9 | $Date$ -->
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| 10 |
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| 11 | <sect2>
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| 12 | <title>Qt Installation Alternatives</title>
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| 13 |
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| 14 | <para>The installation of <application>Qt</application> presents
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| 15 | several challenges and choices. Complicating the Qt installation is the fact
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| 16 | that there are two versions, <application>Qt4</application> and
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| 17 | <application>Qt5</application>, that have executable programs with
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| 18 | identical names. If both packages are installed on one system,
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| 19 | the only methods to manage which set of programs is used is to
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| 20 | either control the users' <envar>PATH</envar> or to rename files
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| 21 | either directly or via symbolic links. Both packages cannot
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| 22 | be installed in the same directory.
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| 23 | </para>
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| 24 |
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| 25 | <para>If you are only going to install one of the Qt versions,
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| 26 | the choice of installation methods is easier. You can either
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| 27 | install the components in the several directories of the <filename
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| 28 | class='directory'>/usr</filename> hierarchy or install the
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| 29 | entire package in a separate directory of your choice. <!-- We
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| 30 | refer to these options below as "Method 1: Installing in /usr"
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| 31 | and "Method 2: Installing in /opt". --></para>
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| 32 |
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| 33 | <para>If both versions of Qt are to be installed, one or both versions need
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| 34 | to be installed in a separate directory. For the purposes here we use the
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| 35 | <filename class='directory'>/opt</filename> directory. The selection of
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| 36 | which version is being used by individual users on a system is controlled
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| 37 | by the <envar>PATH</envar> variable. Other systems can be designed, but
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| 38 | the BLFS editors find the <envar>PATH</envar> method easiest.</para>
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| 39 |
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| 40 | <para> The advantage of installing in <filename
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| 41 | class='directory'>/usr</filename> is that no updates to the
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| 42 | <filename>/etc/ld.so.conf</filename> or
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| 43 | <filename>/etc/man_db.conf</filename> files are required. The package files
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| 44 | are distributed within several subdirectories of the <filename
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| 45 | class='directory'>/usr</filename> hierarchy. This is the method that most
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| 46 | commercial distributions use. The disadvantage for BLFS users is that this
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| 47 | Qt instance cannot be upgraded while it is in use. For instance, it cannot
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| 48 | be upgraded from a running KDE environment. It also precludes having
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| 49 | multiple versions of Qt on your system and does not allow reverting to
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| 50 | an existing, known working instance of Qt.</para>
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| 51 |
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| 52 | <para> The advantage of installing <application>Qt</application> in a
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| 53 | custom directory such as <filename
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| 54 | class='directory'>/opt/qt-&qt4-version;</filename> or <filename
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| 55 | class='directory'>/opt/qt-&qt5-version;</filename> is that it keeps all
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| 56 | the package files consolidated in a dedicated directory hierarchy. By using
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| 57 | this method, an update can be made without overwriting a previous
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| 58 | installation and users can easily revert to a previous version by changing
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| 59 | one symbolic link or merely changing the PATH variable. It also allows a
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| 60 | developer to maintain multiple versions of <application>Qt4</application>
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| 61 | or <application>Qt5</application> for testing. </para>
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| 62 |
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| 63 | </sect2>
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