Building a Relocatable Package

Tying Up the Loose Ends

In the course of building this package, we ran into two hitches:

1. The config file cdp-config couldn't be installed in /etc.

2. The README file 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.

Test-Driving a Relocatable Package

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:

# rpm -qp --queryformat '%{DEFAULTPREFIX}\n' cdplayer-1.0-1.i386.rpm /usr/local #

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:

# rpm -Uvh cdplayer-1.0-1.i386.rpm cdplayer ################################################## #

That seemed to work well enough. Let's see if the files went where we intended:

# ls -al /usr/local/bin total 558 -rwxr-xr-x 1 root root 40739 Oct 7 13:23 cdp* lrwxrwxrwx 1 root root 18 Oct 7 13:40 cdplay -> /usr/local/bin/cdp* … # ls -al /usr/local/man/man1 total 9 -rwxr-xr-x 1 root root 4550 Oct 7 13:23 cdp.1* … #

Looks good. Let's erase the package and reinstall it with a different prefix:

# rpm -e cdplayer # rpm -Uvh --prefix /usr/foonly/blather cdplayer-1.0-1.i386.rpm cdplayer ################################################## #

(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:

# rpm -q --queryformat '%{INSTALLPREFIX}\n' cdplayer /usr/foonly/blather #

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:

# cd /usr/foonly/blather/ # ls -al total 2 drwxr-xr-x 2 root root 1024 Oct 7 13:45 bin/ drwxr-xr-x 3 root root 1024 Oct 7 13:45 man/ #

So far, so good — the proper directories are there. Let's look at the man page first:

# cd /usr/foonly/blather/man/man1/ # ls -al total 5 -rwxr-xr-x 1 root root 4550 Oct 7 13:23 cdp.1* #

That looks ok. Now on to the files in bin:

# cd /usr/foonly/blather/bin # ls -al total 41 -rwxr-xr-x 1 root root 40739 Oct 7 13:23 cdp* lrwxrwxrwx 1 root root 18 Oct 7 13:45 cdplay -> /usr/local/bin/cdp #

Uh-oh. That cdplay symlink isn't right. What happened? If we look at cdplayer's makefile, we see the answer:

install: cdp cdp.1.Z … ln -s /usr/local/bin/cdp /usr/local/bin/cdplay

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:

ln -s /usr/local/bin/cdp /usr/local/bin/cdplay

To:

ln -s ./cdp /usr/local/bin/cdplay

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:

# rpm -Uvh cdplayer-1.0-1.i386.rpm cdplayer ################################################## # cd /usr/local/bin/ # ls -al cdplay lrwxrwxrwx 1 root root 18 Oct 8 22:32 cdplay -> ./cdp* #

Next, we'll try a second install using the --prefix option (after we first delete the original package):

# rpm -e cdplayer # rpm -Uvh --prefix /a/dumb/prefix cdplayer-1.0-1.i386.rpm cdplayer ################################################## # cd /a/dumb/prefix/bin/ # ls -al cdplay lrwxrwxrwx 1 root root 30 Oct 8 22:34 cdplay -> ./cdp* #

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.