[root@rhel include]# gem install pg -- --with-pgsql-include-dir=/usr/pgsql-8.4/include/ --with-pgsql-lib-dir=/usr/pgsql-8.4/lib/
Building native extensions.  This could take a while...
ERROR:  Error installing pg:
	ERROR: Failed to build gem native extension.

/usr/bin/ruby extconf.rb --with-pgsql-include-dir=/usr/pgsql-8.4/include/ --with-pgsql-lib-dir=/usr/pgsql-8.4/lib/
checking for pg_config... yes
Using config values from /usr/bin/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
	--with-opt-dir
	--without-opt-dir
	--with-opt-include
	--without-opt-include=${opt-dir}/include
	--with-opt-lib
	--without-opt-lib=${opt-dir}/lib
	--with-make-prog
	--without-make-prog
	--srcdir=.
	--curdir
	--ruby=/usr/bin/ruby
	--with-pg
	--without-pg
	--with-pg-dir
	--without-pg-dir
	--with-pg-include
	--without-pg-include=${pg-dir}/include
	--with-pg-lib
	--without-pg-lib=${pg-dir}/lib
	--with-pg-config
	--without-pg-config
	--with-pg_config
	--without-pg_config


Gem files will remain installed in /usr/lib/ruby/gems/1.8/gems/pg-0.11.0 for inspection.
Results logged to /usr/lib/ruby/gems/1.8/gems/pg-0.11.0/ext/gem_make.out



[root@rhel include]# find / -name "libpq-fe.h"
/usr/include/libpq-fe.h
/usr/include/postgresql/libpq-fe.h
/usr/pgsql-8.4/include/libpq-fe.h
/usr/local/include/libpq-fe.h
find: `/proc/fs/vmblock/mountPoint': Нет такого файла или каталога