Maximum RPM: Taking the RPM Package Manager to the Limit
Chapter 15. Making a Relocatable Package
For this example, we'll use our tried-and-true cdplayer application.
Let's start by reviewing the spec file for possible problems:
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Everything looks all right, except for the %files list. There are
files in /usr/local/bin, a man page in /usr/local/man/man1, and
a config file in /etc. A prefix of /usr/local would work pretty
well, except for that cdp-config file.
For the sake of this first build, we'll declare the config file
unnecessary and remove it from the %files list. We'll then add a
prefix tag line, setting the prefix to /usr/local. After these
changes are made, let's try a build:
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The build proceeded normally up to the point of actually creating the
binary package. The Package Prefix = usr/local line confirms that RPM
picked up our prefix tag line. But the build stopped — and on a file
called /usr/doc/cdplayer-1.0-1. But that file isn't even in the
%files list. What's going on?
Take a closer look at the %files list. See the line that reads
%doc README? In the Section called The %doc Directive in
Chapter
13,
we discussed how the %doc directive creates a directory under
/usr/doc. That's the file that killed the build — the directory
created by the %doc directive.
Let's temporarily remove that line from the %files list and try again:
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The build completed normally. Note how the files to be placed in the
binary package file are listed, minus the prefix of /usr/local. Some
of you might be wondering why the cdp.1 file didn't cause problems.
After all, it had a %doc directive, too. The answer lies in the way
the file was specified. Since the file was specified using an absolute
path, and that path started with the prefix /usr/local, there was no
problem. A more complete discussion of the %doc directive can be
found in the Section called The %doc Directive in Chapter
13.
In the course of building this package, we ran into two hitches:
-
The config file
cdp-configcouldn't be installed in/etc. -
The
READMEfile could not be packaged using the %doc directive.
Both of these issues are due to the fact that the files' paths do not
start with the default prefix path /usr/local. Does this mean this
package cannot be relocated? Possibly, but there are two options to
consider. The first option is to review the prefix. In the case of our
example, if we chose a prefix of /usr instead of /usr/local, the
README file could be packaged using the %doc directive, since the
default documentation directory is /usr/doc. Another approach would be
to use the %docdir directive to define another documentation-holding
directory somewhere along the prefix path.
[1]
This approach wouldn't work for /etc/cdp-config, though. To package
that file, we'd need to resort to more extreme measures. Basically, this
approach would entail packaging the file in an acceptable directory
(something under /usr/local) and using the %post post-install
script to move the file to /etc. Pointing a symlink at the config file
is another possibility.
Of course, this approach has some problems. First, you'll need to write a %postun script to undo what the %post script does. [2] A %verifyscript that made sure the files were in place would be nice, too. Second, because the file or symlink wasn't installed by RPM, there's no entry for it in the RPM database. This reduces the utility of RPM's -c and -d options when issuing queries. Finally, if you actually move files around using the %post script, the files you move will not verify properly, and when the package is erased, your users will get some disconcerting messages when RPM can't find the moved files to erase them. If you have to resort to these kinds of tricks, it's probably best to forget trying to make the package relocatable.
Looks like cdplayer is a poor candidate for being made relocatable.
However, since we did get a hamstrung version to build successfully, we
can use it to show how to test a relocatable package.
First, let's see if the binary package file's prefix has been recorded properly. We can do this by using the --queryformat option to RPM's query mode:
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The DEFAULTPREFIX tag directs RPM to display the prefix used during
the build. As we can see, it's /usr/local, just as we intended. The
--queryformat option is discussed in the Section called
--queryformat — Construct a Custom Query Response in Chapter
5.
So it looks like we have a relocatable package. Let's try a couple of installs and see if we really can install it in different locations. First, let's try a regular install with no prefix specified:
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That seemed to work well enough. Let's see if the files went where we intended:
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Looks good. Let's erase the package and reinstall it with a different prefix:
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(We should mention that directories foonly and blather didn't exist
prior to installing cdplayer.)
RPM has another tag that can be used with the --queryformat option. It's called INSTALLPREFIX and using it displays the prefix under which a package was installed. Let's give it a try:
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As we can see, it displays the prefix we entered on the command line. Let's see if the files were installed as we directed:
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So far, so good — the proper directories are there. Let's look at the man page first:
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That looks ok. Now on to the files in bin:
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Uh-oh. That cdplay symlink isn't right. What happened? If we look at
cdplayer's makefile, we see the answer:
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Ah, when the software is installed during RPM's build process, the make
file sets up the symbolic link. Looking back at the %files list, we
see cdplay listed. RPM blindly packaged the symlink, complete with its
non-relocatable string. This is why we mentioned absolute symlinks as a
prime example of non-relocatable software.
Fortunately, this problem isn't that difficult to fix. All we need to do is change the line in the makefile that creates the symlink from:
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To:
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Now cdplay will always point to cdp, no matter where it's installed.
When building relocatable packages, relative symlinks are your friend!
After rebuilding the package, let's see if our modifications have the desired effect. First, a normal install with the default prefix:
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Next, we'll try a second install using the --prefix option (after we first delete the original package):
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As you can see, the trickiest part about building relocatable packages is making sure the software you're packaging is up to the task. Once that part of the job is done, the actual modifications are straightforward.
In the next chapter, we'll cover how packages can be built in non-standard directories, as well as how non-root users can build packages.
| [1] | For more information on the %docdir directive, please see the Section called The %docdir Directive in Chapter 13. |
| [2] | Install and erase-time scripts have an environment variable, RPM_INSTALL_PREFIX, that can be used to write scripts that are able to act appropriately if the package is relocated. See the Section called Install/Erase-time Scripts in Chapter 13 for more information. |