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.

15.4.2. 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 section 5.2.2 of Chapter 5, "Getting Information About Packages."

So it looks like we have a relocatable package. Let's try a couple 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 ##################################################

#

Note 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 you can see, it displays the prefix you entered on the command line. Let's see if the files were installed as 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 okay. 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 makefile sets up the symbolic link. Looking back at the %files list, we see cdplay listed. RPM blindly packaged the symlink, complete with its nonrelocatable string. This is why we mentioned absolute symlinks as a prime example of nonrelocatable 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 this:

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

to this:

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 --nodeps 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 --nodeps --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.