pg gem install fails, cannot find libpq-fe.h header
The postgres binaries are not in the path. Symlink them in to a directory in your path and you should be good: ln -s /usr/pgsql-9.4/bin/p* /usr/local/bin
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Did you build postgres or install it from yum?
Just posting the solution for PostgreSQL 11. If someone lands here.
sudo yum install epel-release
sudo yum install postgresql11-llvmjit
sudo yum install postgresql11-devel postgresql11-libs
Then run
gem install pg -v '1.2.3' -- --with-pg-config=/usr/pgsql-11/bin/pg_config
Thats it