Quick automatic install (CentOS 6 / RHEL6)

curl https://raw.githubusercontent.com/Eugeny/ajenti/master/scripts/install-rhel.sh | sh

Quick automatic install (CentOS 7 / RHEL7)

curl https://raw.githubusercontent.com/Eugeny/ajenti/master/scripts/install-rhel7.sh | sh

Manual install

Ajenti requires EPEL repositories: http://fedoraproject.org/wiki/EPEL

Add repository key:

wget http://repo.ajenti.org/ajenti-repo-1.0-1.noarch.rpm 
rpm -i ajenti-repo-1.0-1.noarch.rpm

Install the package:

yum install ajenti

Start the service:

service ajenti restart

The panel will be available on HTTPS port 8000. The default username is root, and the password is admin.

Troubleshooting

Package does not match intended download?

yum clean metadata

Can't access panel at port 8000?

By default, CentOS blocks port 8000 with firewall. Run following to unblock port temporarily. 
CentOS / RHEL 6

iptables -A INPUT -p tcp --dport 8000 -j ACCEPT

Add this line to  /etc/sysconfig/iptables file (before the COMMIT line) to unblock it permanently.

CentOS / RHEL 7

firewall-cmd --permanent --zone=public --add-port=8000/tcp
firewall-cmd --reload