make options

[Kurt Granroth]

On Thursday 20 April 2006 22:38, Nathan England wrote:
> I'm also looking for some documentation that mentions something about the
> DESTDIR or prefix options when make install is run. Some places say to use
> DESTDIR, others say prefix ... ?

Nothing should be saying "use DESTDIR".  That's useful for building RPMs (or 
other packages) but almost never useful for the end user that's compiling 
from source.

The 'prefix' and 'DESTDIR' variables are both part of the autotools suit of 
build tools.  The former says where the files should be installed.  The 
latter describes a temporary installation root for use while packaging.

For instance, all source packages that support both will have their install 
targets set to something like ${DESTDIR}/${prefix}/bin/file.  By default, 
DESTDIR is empty and (on most source packages), prefix defaults 
to /usr/local/.  So this would expand to '/usr/local/bin/file', which is 
where you want it so it's all good.

But say you want to make an RPM.  If you do a 'make install' during the 
packaging process, then it will install it into /usr/local... but what if you 
already have a version of that software there?  Or maybe you don't have 
permissions to install there?  Or you want to maintain a clean system?  
Whatever your reason, you typically do *not* want to install the files into 
your primary system while you are creating the package.

So, instead, you set the DESTDIR to something like '/tmp/build-root'.  Then, 
the file location expands to '/tmp/build-root/usr/local/bin/file'.  When you 
do 'make install' this time, everything is installed into temp.  You can then 
change your root (chroot) to /tmp/build-root and assemble your package at 
your leisure.

The next obvious question is this: why not just set 'prefix' to the full 
'/tmp/build-root/usr/local/bin' when building a binary package?  Well, it's 
due to the fact that quite a few apps actually encode their location one way 
or another into the executable itself.  The most common "automatic" way of 
this happening is encoding the path of associated libraries (using 'rpath') 
into the executable so you don't have to set ld.so.conf for every single 
application install.  If you build the package with the library in 
'/tmp/build-root/usr/local/lib/libmylib.so' but it's installed in the end 
into /usr/local/lib, then the encoded path will be bogus.

In short: Always use 'prefix'.  Only use 'DESTDIR' if you are building RPMs or 
DEBs or something similar.

Here's a quick (not detailed enough) description: 
http://sources.redhat.com/autobook/autobook/autobook_107.html

Kurt