gem install pg 给出 Gem::Ext::BuildError: ERROR: Failed to build gem native extension in ruby '2.2.3' and 'rails', '4.2.7.1' in ubuntu 18.04 LTS

Question

Iam trying to set up a rails project which has ruby 2.2.3 and rails version 4.2.7.1. It uses PostgreSQL as the database. I can see gem 'pg' entry in the GemFile. I did bundle install to install the dependencies, but when it came to installing pg gem, it is giving me the following error. I dont have postgreSQL installed on my ubuntu 18.04 LTS system. Could this be the reason why iam getting this error. Please help. Error that i am getting:

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**Fetching pg 1.2.3
Installing pg 1.2.3 with native extensions
Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
    current directory: /home/pc-123/.rvm/gems/ruby-2.2.3/gems/pg-1.2.3/ext
/home/pc-123/.rvm/rubies/ruby-2.2.3/bin/ruby -I /home/pc-123/.rvm/rubies/ruby-2.2.3/lib/ruby/site_ruby/2.2.0 -r ./siteconf20200822-841-6si3xn.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/pc-123/.rvm/rubies/ruby-2.2.3/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

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Answer 1

You must install the libpq-dev package. You are using Ubuntu so:

sudo apt install libpq-dev

Answer 2

It would be smart to have PostGreSQL installed.

This depends on what Ruby version is your interpreter using. A mismatch there and you can run into problems. Using the same version will fix your issue.