1、下载xinetd安装包

wget http://archive.ubuntu.com/ubuntu/pool/universe/x/xinetd/xinetd_2.3.15.3-1_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/n/netkit-telnet/telnetd_0.17-41_amd64.deb

2、安装

dpkg -i xinetd_2.3.15.3-1_amd64.deb telnetd_0.17-41_amd64.deb

3、如果遇到报错invoke-rc.d: policy-rc.d denied ，请尝试以下解决方案

printf '#!/bin/sh\nexit 0' > /usr/sbin/policy-rc.d
chmod +x  /usr/sbin/policy-rc.d

printf 'service telnet
{
        disable = no
        flags = REUSE
        socket_type = stream
        wait = no
        user = root
        server = /usr/sbin/in.telnetd
        log_on_failure = HOST
}' > /etc/xinetd.d/telnet
systemctl restart xinetd.service