1. To change the order of PATH items, you just need to put the newly-added path in front of the PATH, or at the back of the path to put it behind all the former PATH items.
2. Compile opencv on linux, this is a good helper: http://blog.sina.com.cn/s/blog_675e6b570101gpsj.html
3. Compile hdf5 on centos, a good helper is here: http://www.hdfgroup.org/ftp/HDF5/current/src/unpacked/release_docs/INSTALL
4. compile leveldb on centos, a good helper: http://techoverflow.net/blog/2012/12/14/compiling-installing-leveldb-on-linux/
5. compile protobuf, about the error cannot install `libprotoc.la' to a directory not ending in /usr/local/lib : solution is : https://www.mail-archive.com/protobuf@googlegroups.com/msg02998.html; http://stackoverflow.com/questions/10279829/installing-glib-in-non-standard-prefix-fails;
https://code.google.com/p/protobuf/issues/detail?id=549;
And the installation helper is here: http://blog.csdn.net/realxie/article/details/7456013
6.compile boost library: http://www.boost.org/doc/libs/1_57_0/more/getting_started/unix-variants.html