[OS_Linux_Ubuntu] telnet & ssh 설치와 설정 (installation / configuration)


1. telnet 설치 및 설정
sudo apt-get install xinetd
sudo apt-get install telnetd

/etc/xinetd.conf 파일의 defualt{} 함수는 주석 처리

service telnet
{
     disable = no
     flags = REUSE
     socket_type = stream
     wait = no
     user = root
     server = /usr/sbin/in.telnetd
     log_on_failure += USERID
}

sudo /etc/init.d/xinetd restart


2. ssh 설치 및 설정
설치

    $ sudo apt-get install ssh

포트 변경

    $ sudo vim /etc/ssh/sshd_config

    # port 22 에서 '#' 를 제거하고 원하는 포트로 변경

    IF >>  X-window 사용하고 싶을 경우, 
        
        /etc/ssh/ssh_config
        위의 파일의 다음내용을 변경한다
       
        # ForwardX11 no -> ForwardX11 yes 로 설정변경)

데몬 재시작

    $ sudo /etc/init.d/ssh restart

서버 작동 확인

    $ netstat -ntlp | grep 23



Ubuntu는 /etc/hosts.allow 파일과  /etc/hosts.deny 파일에 모든 서비스에 대한 허용과 거절을 설정한다. 
설정 예시>  hosts.deny 파일에는 보통 ALL : ALL 로 해준다.(보안의 기본 정책은 모든 접속을 차단하고 승인된 IP만 허용한다)
  서비스(ssh/telnet)을 우분투 서버가 있는 네트워크(192.168.123.0/24)와 관리자 IP(10.10.10.100)을 허용하고자 한다면 
  hosts.deny 는 
     ALL : ALL
  hosts.allow 은
     sshd : 10.10.10.100, 192.168.123.0/255.255.255.0
     in.telnetd : 10.10.10.100, 192.168.123.0/255.255.255.0 
상기와 같이 설정한다.
로컬에서 로컬로의 모든 접속을 허용하려면  hosts.allow 파일에  ALL:localhost 를 추가 해주면 된다.

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