On Linux system, if we do not have root priviledge, we can not use package
managers to install a package to its default location (usually under /usr).
Besides, the packages installed by the package managers are often too old to
have the latest features. Or, even if we have root priviledge, we do not want
to mess up with the system-wide packages and just want to experiment with a
package locally. On these ocassions, we may want to install the package to a
custom location.
The standard procedure to build and install a package from source is something like the following:
./configure
make && make install
By default, the package will be installed under /usr and you must have root
priviledge. If you are not familiar with these steps. Read
here
and
here
for more discussions on what each step does.
In order to install the package to a custom location and find dependency
packages which are not installed on standard locations, we need to set custom
options and variables for the configure script. In this post, I will explain
the meaning of --prefix, CLFAGS, CXXFLAGS, CPPFLAGS and LDFLAGS.
The meaning of these options and variables#
--prefix#
--prefix is used to tell make where to install the compiled packages. For
example, if you use --prefix=$HOME/local, after building the package using
make -j, if you do a make install, the binary file will be put in
$HOME/local/bin, the library file will be put in $HOME/local/lib or
$HOME/local/lib64, the header file will be put in $HOME/local/include and
the help file and other resources may be put in $HOME/local/share.
CFLAGS and CXXFLAGS#
CFLAGS and CXXFLAGS are used to set up C and C++ compilers respectively. On
most Linux system, the C compiler is usually gcc, while the C++ compilers is
usually g++.
CPPFLAGS#
The CPPFLAGS is often mis-understood to set up C++ compiler options. In fact,
it is used by C/C++ preprocessors. It tells preprocessor where to find the
header files. If you need to set up C++ compiler, you should use CXXFLAGS
variable. A valid CPPFLAGS is something like
CPPFLAGS="-I$HOME/local/include".
LDFLAGS#
LDFLAGS is used to set up the path of library files. For example,
LDFLAGS="-L$HOME/local/lib".
Conclusion#
In this post, I introduced some of the most commonly-used options and flags for the configure script when building packages from source. Understanding these options and flags will help you succeed in building the packages.