Move into /usr/src/
cd /usr/src/Download Asterisk from their website
wget http://downloads.asterisk.org/pub/telephony/asterisk/asterisk-20-current.tar.gzExtract the downloaded archive
tar zxvf asterisk-20-current.tar.gzOptionally, remove the archive
rm asterisk-20-current.tar.gzMove into the new directory
cd asterisk-20.5.2/Run the install script
contrib/scripts/install_prereq installRun the configure script
./configureSelect and modules to be installed
make menuselectCompile Asterisk
makeInstall Asterisk on the system
make installOPTIONAL: Generate sample config files and move them into the sample directory
make samples
mkdir /etc/asterisk/samples
mv /etc/asterisk/*.* /etc/asterisk/samples/OPTIONAL: Generate files that make up a basic PBX config
make basic-pbxGenerate startup files
make configEnable and start Asterisk
systemctl enable asterisk.service
systemctl start asterisk.service
systemctl status asterisk.serviceYou should now be able to launch the Asterisk CLI and further configure the system
asterisk -rvvvv