ubuntu ssh install (우분투 ssh 설치)


install ssh

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$ apt-get install openssh-server
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start ssh

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$ service ssh restart
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confirm Installation

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$ dpkg --get-selections | grep openssh
openssh-client                    install
openssh-server                    install
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$ service ssh status
● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: active (running) since 일 2018-12-09 00:35:18 KST; 1 day 17h ago
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test connection

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$ ssh <user ID>@<IP or HostName>
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ubuntu version check (우분투 버전 확인)


check ubuntu version

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$ cat /etc/issue
Ubuntu 16.04.4 LTS \n \l
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$ lsb_release -a
No LSB modules are available.
Distributor ID:    Ubuntu
Description:    Ubuntu 16.04.4 LTS
Release:    16.04
Codename:    xenial
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ubuntu telnet server install (우분투 텔넷 서버 설치)


install telnet server (텔넷 서버 설치)


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$ sudo apt-get install xinetd telnetd

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Configure telnet server (텔넷 서버 설정)

add below script on /etc/xinetd.d/telnet 

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$ vi /etc/xinetd.d/telnet
 
-----------------------
 
# default: off
service telnet
{
 disable = no
 flags = REUSE
 socket_type = stream
 wait = no
 user = root
 server = /usr/sbin/in.telnetd
 log_on_failure += USERID
}

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Start telnet server (텔넷 서버 실행)

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$ sudo /etc/init.d/xinetd restart
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Check telnet server (텔넷 서버 테스트)

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$ telnet < IP or HostName >
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or

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$ telnet
telnet> open
(to) < IP or HostName
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if this error occurs, you should check ACL.

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$ telnet 192.88.19.11 23
Trying 192.88.19.11...
telnet: connect to address 192.88.19.11: Connection refused
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scan port


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$ nmap -A <from IP>/32 -p 23
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23 port is closed 


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$ nmap -192.88.19.23/32 -23
 
Starting Nmap 7.01 ( https://nmap.org ) at 2018-12-10 13:08 KST
Nmap scan report for aaa.com (192.88.19.23)
Host is up (0.0014s latency).
PORT   STATE  SERVICE VERSION
23/tcp closed telnet
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open 23 ports . be careful of openning ACL

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$ sudo iptables -A IN_public_allow -p tcp -m tcp --dport 23 -m conntrack --ctstate NEW -j ACCEP
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connect telnet


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$ telnet 192.88.19.11 23
Trying 192.88.19.11...
Connected to aaa.com.
Escape character is '^]'.
Password:
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done.


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