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<TITLE>Maximum RPM (RPM):Inside the Spec File:EarthWeb Inc.-</TITLE>
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<!-- ISBN=0672311054 //-->
<!-- TITLE=Maximum RPM (RPM)//-->
<!-- AUTHOR=Edward Bailey//-->
<!-- PUBLISHER=Macmillan Computer Publishing//-->
<!-- IMPRINT=Sams//-->
<!-- CHAPTER=13 //-->
<!-- PAGES=0163-0204 //-->
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<A NAME="PAGENUM-182"><P>Page 182</P></A>
<P>Because there will be no blather packages installed once the erase completes, the
argument passed to the scripts is 0.
</P>
<P>With all that said, of what possible use would this argument be? Well, it has two very
interesting properties:
</P>
<UL>
<LI> When the first version of a package is installed, its
%pre and %post scripts will be passed an argument equal to
1.
<LI> When the last version of a package is erased, its
%preun and %postun scripts will be passed an argument equal to
0.
</UL>
<P>Given these properties, it's trivial to write an install-time script that can take certain actions
in specific circumstances. Usually, the argument is used in the
%preun or %postun scripts to perform a special task when the last instance of a package is being erased.
</P>
<P>What is normally done during these scripts? The exact tasks may vary, but in general, the
tasks are any that need to be performed at these points in the package's existence. One very
common task is to run ldconfig when shared libraries are installed or removed. But that's not the
only use for these scripts. It's even possible to use the scripts to perform tests to ensure the
package install/erasure should proceed.
</P>
<P>Since each of these scripts will be executing on whatever system installs the package, it's
necessary to choose the script's choice of tools carefully. Unless you're sure a given program is
going to be available on all the systems that could possibly install your package, you should not use
it in these scripts.
</P>
<B>
13.3.2.1. The %pre Script
</B>
<P>The %pre script executes just before the package is to be installed.
It is the rare package that requires anything to be done prior to installation; none of the 350 packages that comprise
Red Hat Linux 4.0 make use of it.
</P>
<B>
13.3.2.2. The %post Script
</B>
<P>The %post script executes after the package has been installed. One of the most popular
reasons a %post script is needed is to run
ldconfig to update the list of available shared
libraries after a new one has been installed. Of course, other functions can be performed in a
%post script. For example, packages that install shells use the
%post script to add the shell name to /etc/shells.
</P>
<P>If a package uses a %post script to perform some function, quite often it will include a
%postun script that performs the inverse of the
%post script, after the package has been removed.
</P>
<A NAME="PAGENUM-183"><P>Page 183</P></A>
<B>
13.3.2.3. The %preun Script
</B>
<P>If there's a time when your package needs to have one last look around before the user erases
it, the place to do it is in the %preun script. Anything that a package needs to do immediately
prior to RPM taking any action to erase the package can be done here.
</P>
<B>
13.3.2.4. The %postun Script
</B>
<P>The %postun script executes after the package has
been removed. It is the last chance for a package to clean up after itself. Quite often,
%postun scripts are used to run ldconfig to remove newly erased shared libraries from
ld.so.cache.
</P>
<H4><A NAME="ch13_ 7">
13.3.3. Verification-Time Script—The
%verifyscript Script
</A></H4>
<P>The %verifyscript script executes whenever the installed
package is verified by RPM's verification command. The contents of this script are entirely up to the package builder, but in
general the script should do whatever is necessary to verify the package's proper installation.
Since RPM automatically verifies the existence of a package's files, along with other file
attributes, the %verifyscript script should concentrate on different aspects of the package's
installation. For example, the script might ensure that certain configuration files contain the proper
information for the package being verified:
</P>
<!-- CODE //-->
<PRE>
for n in ash bsh; do
echo -n "Looking for $n in /etc/shells... "
if ! grep "^/bin/${n}\$" /etc/shells > /dev/null; then
echo "missing"
echo "${n} missing from /etc/shells" >&2
else
echo "found"
fi
done
</PRE>
<!-- END CODE //-->
<P>In this script, the config file /etc/shells is checked to ensure that it has entries for the
shells provided by this package.
</P>
<P>It is worth noting that the script sends informational and error messages to
stdout and error messages only to stderr. Normally RPM will only display error output from a verification
script; the output sent to stdout is only displayed when the verification is run in verbose mode.
</P>
<H3><A NAME="ch13_ 8">
13.4. Macros: Helpful Shorthand for Package Builders
</A></H3>
<P>RPM does not support macros in the sense of ad hoc sequences of commands being defined
as a macro and executed by simply referring to the macro name.
</P>
<A NAME="PAGENUM-184"><P>Page 184</P></A>
<P>However, two parts of RPM's build process are fairly constant from one package to
another: the unpacking and patching of sources. RPM makes two macros available to simplify
these tasks:
</P>
<UL>
<LI> The
%setup macro, which is used to unpack the original sources.
<LI> The
%patch macro, which is used to apply patches to the original sources.
</UL>
<P>These macros are used exclusively in the %prep script; it wouldn't make sense to use them
anywhere else. The use of these macros is not mandatory—it is certainly possible to write a
%prep script without them. But in the vast majority of cases they make life easier for the package builder.
</P>
<H4><A NAME="ch13_ 9">
13.4.1. The %setup Macro
</A></H4>
<P>As mentioned earlier, the %setup macro is used to unpack the original sources, in
preparation for the build. In its simplest form, the macro is used with no options and gets the name of
the source archive from the source tag specified earlier in the spec file. Let's look at an
example. The cdplayer package has the following source tag:
</P>
<!-- CODE SNIP //-->
<PRE>
Source: ftp://ftp.gnomovision.com/pub/cdplayer/cdplayer-1.0.tgz
</PRE>
<!-- END CODE SNIP //-->
<P>and the following %prep script:
</P>
<!-- CODE SNIP //-->
<PRE>
%prep
%setup
</PRE>
<!-- END CODE SNIP //-->
<P>In this simple case, the %setup macro expands into the following commands:
</P>
<!-- CODE //-->
<PRE>
cd /usr/src/redhat/BUILD
rm -rf cdplayer-1.0
gzip -dc /usr/src/redhat/SOURCES/cdplayer-1.0.tgz | tar -xvvf -
if [ $? -ne 0 ]; then
exit $?
fi
cd cdplayer-1.0
cd /usr/src/redhat/BUILD/cdplayer-1.0 chown -R root.root .
chmod -R a+rX,g-w,o-w .
</PRE>
<!-- END CODE //-->
<P>As you can see, the %setup macro starts by changing directory into RPM's build area and
removing any cdplayer build trees from previous builds. It then uses
gzip to uncompress the original source (whose name was taken from the
source tag), and pipes the result to tar for unpacking. The return status of the unpacking is tested. If successful, the macro continues.
</P>
<P>At this point, the original sources have been unpacked. The
%setup macro continues by changing directory into
cdplayer's top-level directory. The two cd commands are an artifact of
%setup's macro expansion. Finally, %setup makes sure every file in the build tree is owned by root
and has appropriate permissions set.
</P>
<P>But that's just the simplest way that %setup can be used. A number of other options can
be added to accommodate different situations. Let's look at them.
</P>
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