必要ライブラリがありません事案の救世主apt-file

gemなど入れる時の哀しみ

Gem::Installer::ExtensionBuildError: ERROR: Failed to build gem native extension.

        /home/hash/.rvm/rubies/ruby-1.9.3-p327/bin/ruby extconf.rb
checking for pg_config... no
No pg_config... trying anyway. If building fails, please try again with
 --with-pg-config=/path/to/pg_config
checking for libpq-fe.h... no
Can't find the 'libpq-fe.h header
*** extconf.rb failed ***

何入れたらいいもんだかわからない. そこでapt-file

$ sudo apt-get install apt-file
$ apt-file update
$ apt-file search libpq-fe.h
libpq-dev: /usr/include/postgresql/libpq-fe.h

$ sudo apt-get install libpq-dev

素晴らしい