sudo yum remove postgresql

In order to confirm we are removing what we did install with amazon-linux-extras, we can check the Repository after we run the sudo yum remove command:

yum remove openvpn

read

man yum

for further information.

If you still have the original compiled source directory somewhere you may be able to use sudo make uninstall in each directory which (in theory) should remove all of the files installed.

Note I say in theory because it's not guaranteed the Makefile has proper provision for "uninstalling" in this way. Generally the recommendation is to use packages shipped with the distribution unless you're fully aware of what you're doing and have a strategy for handling upgrades & uninstalling applications installed this way.

If you are using RHEL or Amazon's AMI:

sudo yum -y remove mysql-server

and

sudo yum -y install mysql-server

should do it.

If it's Amazon AMI Linux first you need to stop nginx service:

sudo service nginx stop

than you should disable it with:

sudo chkconfig nginx off

and if you like, uninstall it:

sudo yum remove nginx

HTH

1. remove dispensable packages

Amazon Linux instances manage their software using the yum package manager. The yum package manager can install, remove, and update software, as well as manage all of the dependencies for each package. – Managing Software on Your Linux Instance

I have executed the following to produce a list of the 20 largest packages in the system:

rpm -qa --queryformat '%10{size} - %-25{name} \t %{version}\n' | sort -nr | head -n 20

To remove packages with all of its dependencies I have then installed the yum plugin remove-with-leaves and then repeatedly removed the largest packages (including dependencies) which I deemed dispensable (see below for list):

sudo yum remove package_name --remove-leaves

2. remove obsolete kernel

1. Identified current kernel:uname -mrs
2. Listed all kernels: rpm -q kernel
3. Manually removed obsolete Linux kernel: sudo yum remove kernel-4.9.76-3.78.amzn1.x86_64

3. remove unused packages

Identified packages that can be removed without affecting anything else (in debian-speak these are called “orphaned packages”) and removed quietly.

sudo package-cleanup --quiet --leaves | sudo xargs -l1 yum -y remove 

Findings

While I am actively only using Python 3.6.5 it is not possible to remove the default python (Python 2.7.14).

Python is required by many of the Linux distributions. Many system utilities the distro providers combine (both GUI based and not), are programmed in Python. The version of python the system utilities are programmed in I will call the "main" python. [...] Because of the system utilities that are written in python it is impossible to remove the main python without breaking the system. – How to yum remove Python gracefully?

Space occupied by python27 packages amounts to 115819035 bytes (~116 MB).

Results

• A total of ~0.5 GB was reclaimed (7% of disk space on /dev/xvda1).
• 214 packages with a total of 633427867 bytes were removed:

  java-1.7.0-openjdk emacs-common mysql55-server java-1.7.0-openjdk-devel git 
  mysql55 vim-common perl compat-libicu4 aws-apitools-ec2 emacs v8 ruby20-libs 
  perl-Encode nodejs-devel aws-apitools-elb aws-apitools-as nodejs 
  aws-apitools-mon perl-DBD-SQLite dejavu-sans-fonts subversion subversion-libs 
  subversion-perl python36-devel dejavu-serif-fonts vim-enhanced libtool autoconf 
  perl-DBI rubygem20-rdoc automake libX11-common perl-libs gyp cvs libX11 git-svn 
  alsa-lib gnutls dejavu-sans-mono-fonts perl-Net-SSLeay npm libyaml-devel 
  xorg-x11-fonts-Type1 perl-IO-Compress rsync libxcb libpng perl-Test-Harness 
  rubygems20 perl-Pod-Simple fontconfig aws-amitools-ec2 lcms2 perl-DBD-MySQL55 
  git-cvs xorg-x11-font-utils libXfont perl-podlators perl-IO-Socket-SSL git-p4 
  v8-devel perl-YAML perl-Storable rubygem20-json perl-Git-SVN perl-PathTools 
  nodejs-hawk perl-Pod-Perldoc ruby20-irb perl-File-Temp libuv-devel libserf 
  system-rpm-config autogen-libopts perl-Getopt-Long perl-Compress-Raw-Zlib 
  perl-Filter perl-GSSAPI dejavu-fonts-common libuv perl-Net-Daemon libICE cvsps 
  perl-Socket rubygem20-psych perl-Digest-SHA git-email perl-Authen-SASL ttmkfdir 
  perl-HTTP-Tiny perl-Data-Dumper nodejs-ctype perl-threads emacs-git 
  perl-Time-HiRes perl-IO-Socket-IP libXext giflib rubygem20-bigdecimal libSM 
  nodejs-async perl-threads-shared perl-PlRPC nodejs-hoek node-gyp libXi perl-Git 
  nodejs-request nodejs-fstream perl-Scalar-List-Utils ruby20 nodejs-mime 
  perl-Exporter perl-TermReadKey perl-Compress-Raw-Bzip2 nodejs-tar 
  perl-Digest-MD5 perl-File-Path perl-Error http-parser perl-Net-LibIDN 
  perl-Pod-Usage perl-Time-Local libfontenc libXrender libXau 
  nodejs-npm-registry-client nodejs-minimatch nodejs-boom nodejs-http-signature 
  nodejs-semver libXcomposite nodejs-glob nodejs-nopt perl-Digest perl-Carp 
  libXtst perl-Thread-Queue nodejs-npmconf libffi-devel perl-constant gpm-libs 
  perl-Pod-Escapes nodejs-normalize-package-data nodejs-packaging 
  nodejs-read-package-json nodejs-promzard nodejs-lockfile nodejs-asn1 
  nodejs-ansi perl-Text-ParseWords copy-jdk-configs nodejs-form-data nodejs-sntp 
  nodejs-fstream-npm nodejs-node-uuid nodejs-config-chain perl-Digest-HMAC 
  nodejs-retry nodejs-graceful-fs nodejs-sigmund nodejs-npmlog http-parser-devel 
  nodejs-read-installed nodejs-lru-cache nodejs-init-package-json nodejs-qs 
  nodejs-slide nodejs-combined-stream nodejs-assert-plus nodejs-fstream-ignore 
  nodejs-block-stream perl-parent nodejs-delayed-stream nodejs-ini nodejs-sha 
  nodejs-cmd-shim nodejs-tunnel-agent nodejs-mute-stream nodejs-rimraf 
  nodejs-read nodejs-osenv nodejs-mkdirp perl-macros nodejs-which nodejs-abbrev 
  perl-Net-SMTP-SSL nodejs-archy nodejs-uid-number nodejs-aws-sign 
  nodejs-forever-agent nodejs-opener nodejs-json-stringify-safe nodejs-proto-list 
  nodejs-cryptiles nodejs-editor nodejs-child-process-close 
  nodejs-github-url-from-git nodejs-cookie-jar nodejs-npm-user-validate 
  nodejs-chmodr nodejs-chownr nodejs-once nodejs-inherits nodejs-oauth-sign 
  aws-apitools-common mysql-config vim-filesystem ruby git-all 
  fontpackages-filesystem 
  

Resources

1. Amazon Linux AMI
   • Amazon Linux AMI 2018.03 Release Notes
2. GAD3R's answer to how to remove all installed dependent packages while removing a package in centos 7?
3. How to remove old unused kernels on CentOS Linux
4. jtoscarson's answer to Remove unused packages
5. Owen Fraser-Green's answer to How can I remove Orphan Packages in Fedora?