ver time I have added way too many PPAs using the add-apt-repository command on Ubuntu Linux 16.04/18.04 LTS server for testing purpose. How can I delete or remove those PPAs? Is there a command to list all PPAs?
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Yes, you can delete or remove a PPA. You must have root privileges to achieve this task.
What is a PPA?
A PPA is an acronym for Personal Package Archive. It is nothing but pre-built binary software repository for apt packages. The author uploads source code and packages are built online using Launchpad.
How do I add a PPA and install a package?
The syntax is:
sudo add-apt-repository ppa:name/her
sudo apt update
sudo apt install package
For example, install a simple animated GIF screen recorder called peek using PPA:
$ sudo add-apt-repository ppa:peek-developers/stable
$ sudo apt update
$ sudo apt install peek
How to list all installed PPAs
Type the following command:
$ grep ^ /etc/apt/sources.list.d/*
Sample outputs:

How To: Ubuntu Linux Remove/Delete PPAs
The syntax is:
sudo add-apt-repository --remove ppa:name/here
To remove PPA named ppa:gluster/glusterfs-3.9. However, before removing PPA delete all packages installed from the same PPA using apt-get command/apt command:
$ sudo apt-get --purge remove glusterfs-server
$ sudo apt-get --purge autoremove
Now delete PPA:
$ sudo add-apt-repository --remove ppa:gluster/glusterfs-3.9
Sample outputs:
This archive is EOL. Please use a supported version. More info: https://launchpad.net/~gluster/+archive/ubuntu/glusterfs-3.9 Press [ENTER] to continue or ctrl-c to cancel removing it
Finally update your repo:
$ sudo apt-get update
Sample outputs:
Hit:1 http://ppa.launchpad.net/saiarcot895/myppa/ubuntu xenial InRelease Hit:2 http://download.nus.edu.sg/mirror/mariadb/repo/10.1/ubuntu xenial InRelease Get:3 http://security.ubuntu.com/ubuntu xenial-security InRelease [102 kB] Hit:4 http://mirror.lstn.net/mariadb/repo/10.1/ubuntu xenial InRelease Hit:5 http://in.archive.ubuntu.com/ubuntu xenial InRelease Hit:6 http://in.archive.ubuntu.com/ubuntu xenial-updates InRelease Get:7 http://in.archive.ubuntu.com/ubuntu xenial-backports InRelease [102 kB] Fetched 204 kB in 1s (185 kB/s) Reading package lists... Done
Say hello to ppa-purge tool
The ppa-purge tool is nothing but a bash shell script capable of downgrading all packages in a given PPA back to the original Ubuntu versions. It disables a PPA. First install ppa-purge:
$ sudo apt-get install ppa-purge
Sample outputs:
Reading package lists... Done Building dependency tree Reading state information... Done Suggested packages: aptitude The following NEW packages will be installed: ppa-purge 0 upgraded, 1 newly installed, 0 to remove and 4 not upgraded. Need to get 6,312 B of archives. After this operation, 24.6 kB of additional disk space will be used. Get:1 http://in.archive.ubuntu.com/ubuntu xenial/universe amd64 ppa-purge all 0.2.8+bzr63 [6,312 B] Fetched 6,312 B in 0s (24.2 kB/s) Selecting previously unselected package ppa-purge. (Reading database ... 92785 files and directories currently installed.) Preparing to unpack .../ppa-purge_0.2.8+bzr63_all.deb ... Unpacking ppa-purge (0.2.8+bzr63) ... Processing triggers for man-db (2.7.5-1) ... Setting up ppa-purge (0.2.8+bzr63) ...
ppa-purge syntax
The syntax is:
$ sudo ppa-purge ppa:repo-name/dirname
$ sudo ppa-purge ppa:saiarcot895/mypp
Sample outputs:

To remove https://launchpad.net/~saiarcot895/+archive/ubuntu/myppa you can use following syntax too:
$ sudo ppa-purge -o myppa
$ sudo ppa-purge -o saiarcot895 -p myppa
Where,
-p [ppaname] PPA name to be disabled (default: ppa) -o [ppaowner] PPA owner -s [host] Repository server (default: ppa.launchpad.net) -d [distribution] Override the default distribution choice. -y Pass -y --force-yes to apt-get or -y to aptitude -i Reverse preference of apt-get upon aptitude. -h Display this help text