Configure the Telnet server in Ubuntu10.10

First describe my system environment: Ubuntu10.10x86Desktop in this system by default only installed telnet (that is, the client) root@www.linuxidc.com :~ # Dpkg-stelnetPackage: telnetStatus: installokinstalled & nb first describe my system environment: Ubuntu 10.10x86 Desktop

By default, only telnet (client) is installed on this system)

 
 

  
  
root@www.linuxidc.com:~# dpkg -s telnet 
  
  
Package: telnet 
  
  
Status: install ok installed 
  
  
Priority: standard 
  
  
Section: net 
  
  
Installed-Size: 188 
  
  
Maintainer: Ubuntu Developers     
  
  
Architecture: i386 
  
  
Source: netkit-telnet 
  
  
Version: 0.17-36build1 
  
  
Replaces: netstd 
  
  
Provides: telnet-client 
 
 

Therefore, only telnet commands can be used to log on to the host where the telnet service is enabled. Others cannot use telnet to log on to the host.

1. Now we want to talk about how to allow others to use telnet to log on to the local machine. We need to install two software:

 
 

  
  
root@www.linuxidc.com:~# apt-get install telnetd 
  
  
root@www.linuxidc.com:~# apt-get install xinetd 
 
 

Telnetd is telnet-server, but it cannot be started by itself. You need to manage the daemon software xinetd to take over.

 
 

  
  
root@www.linuxidc.com:~# dpkg -s telnetd 
  
  
Package: telnetd 
  
  
Status: install ok installed 
  
  
Priority: optional 
  
  
Section: net 
  
  
Installed-Size: 152 
  
  
Maintainer: Ubuntu Developers     
  
  
Architecture: i386 
  
  
Source: netkit-telnet 
  
  
Version: 0.17-36build1 
  
  
Replaces: netstd 
  
  
Provides: telnet-server 
 
 

2. Start telnetd through xinetd by creating a new telnet file and entering the following content (no security settings)

 
 

  
  
Root@www.linuxidc.com :~ # Vi/etc/xinetd. d/telnet
  
  
Service telnet
  
  
{
  
  
Disable=No 
  
  
Socket_type=Stream 
  
  
Flags=REUSE 
  
  
Wait=No 
  
  
User=Root 
  
  
Server=/Usr/sbin/In. telnetd# Note that in. telnetd is the file generated by telnetd installation.
  
  
Log_on_failure + = USERID
  
  
}
 
 

If you want to modify the default port number for telnet (23), you need to modify the corresponding telnet port in the/etc/services file.

3. Restart the xinetd program.

 
 

  
  
root@www.linuxidc.com:/etc/xinetd.d# service xinetd restart 
  
  
 * Stopping internet superserver xinetd                                  [ OK ]  
  
  
 * Starting internet superserver xinetd                                  [ OK ] 
 
 

In this case, you can use the netstat command to check the listening status of port 23.

 
 

  
  
root@www.linuxidc.com:~# netstat -tulnp | grep 23 
  
  
tcp        0      0 0.0.0.0:23              0.0.0.0:*               LISTEN      4176/xinetd  
 
 

4. You can confirm that the telnet server has been set up. In this case, you only need to change the computer and then use the telnet ip address to log on. The default setting is that the root user cannot log on via telnet (telnet is transmitted in plain text on the network, and the password can be detected by sniffer). If the security is ensured, you can use the following method to allow the root user to log on:

(1) modify the/etc/securetty file and add the terminal

 
 

  
  
root@www.linuxidc.com:~# tail -5 /etc/securetty  
  
  
pts/0 
  
  
pts/1 
  
  
pts/2 
  
  
pts/3 
  
  
pts/4 
 
 

Or you can directly change the name of the securetty file to use root login.

(2) modify the/etc/pam. d/login file and call the securetty verification Annotation

 
 

  
  
12  # Disallows root logins except on tty's listed in /etc/securetty 
  
  
13  # (Replaces the `CONSOLE' setting from login.defs) 
  
  
14  # Note that it is included as a "required" module. root will be 
  
  
15  # prompted for a password on insecure ttys. 
  
  
16  # If you change it to a "requisite" module, make sure this does not leak 
  
  
17  # user name information. 
  
  
18  #auth       required  pam_securetty.so 
 
 

In this way, the telnet configuration is basically complete, but we recommend that you use ssh (however, for windows systems, you need to append dedicated software to ssh, which is really amazing!