Gem::Ext::BuildError: ERROR: Failed to build gem native extension.

current directory:
/home/meni/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/pg-1.1.4/ext
/home/meni/.rbenv/versions/2.6.0/bin/ruby -I
/home/meni/.rbenv/versions/2.6.0/lib/ruby/2.6.0 -r
./siteconf20190220-2326-1eh1ckf.rb 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 ***
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=/home/meni/.rbenv/versions/2.6.0/bin/$(RUBY_BASE_NAME)
	--with-pg
	--without-pg
	--enable-windows-cross
	--disable-windows-cross
	--with-pg-config
	--without-pg-config
	--with-pg_config
	--without-pg_config
	--with-pg-dir
	--without-pg-dir
	--with-pg-include
	--without-pg-include=${pg-dir}/include
	--with-pg-lib
	--without-pg-lib=${pg-dir}/lib

To see why this extension failed to compile, please check the mkmf.log which can
be found here:

/home/meni/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/extensions/x86_64-linux/2.6.0-static/pg-1.1.4/mkmf.log

extconf failed, exit code 1

Gem files will remain installed in
/home/meni/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/gems/pg-1.1.4 for
inspection.
Results logged to
/home/meni/.rbenv/versions/2.6.0/lib/ruby/gems/2.6.0/extensions/x86_64-linux/2.6.0-static/pg-1.1.4/gem_make.out

An error occurred while installing pg (1.1.4), and Bundler cannot
continue.
Make sure that `gem install pg -v '1.1.4' --source 'https://rubygems.org/'`
succeeds before bundling.

In Gemfile:
  pg