Remote Connectivity

 Telnet is used to communicate to a host through telnet protocol on default port 23  It operates on client/server basic.. The client requires an account on the server to login  Most t

 Configure FTP

 Telnet is used to communicate to a host

through telnet protocol on default port 23

 It operates on client/server basic The client requires an account on the server to login

 Most telnet servers will not allow you

login as root because of security You can

login as normal user and su to root

 why people still use it ? - telnet can be used for debugging text based protocol : HTTP, SMTP and POP

 When users has telnetrc file in their home directories, telnet will execute the

commands listed in this file

# this is a comment

saigonctt send ayt DEFAULT environ export USER

telnet [IP address|host name] [port]

 If telnet is executed without options, it will be

started in command mode with prompt

“telnet>”

 You can change to command mode by

“Ctrl-]” after connected

?, h, help Lists commands with description

<command> ? More information of command (arg)

open <IP address> Open connection to the IP address or host name close = quit Terminates connection from client

logout Requests server to terminate the connection

send Send a special character sequence to the server

status A brief status report of telnet

…

( See #man telnet for more commands )

 There are 3 programs :

 rlogin : similar to telnet

rlogin [-l username] <hostname>

 rsh : executes cmd on remote host

rsh [-l username] <hostname> <cmd>

Shell meta-characters can be used in <cmd> To have rsh

interpret the meta-characters on remote machine, put

`quotation mark around them If not

quotes,meta-characters are interpreted on local machine :

# rsh –l minh saigonctt “cat ~/file” > local_file

# rsh –l minh saigonctt “cat ~/file” “>” remote_file

 rcp : copy files between machines

rcp <dir> <remote username>@<hostname>:<dir> rcp <remote username>@<hostname>:<dir> <dir>

 centers around the idea of trusted users

and hosts , NOT password authentication.

• Trusted hosts are also known as equivalent hosts

• If NO hosts.equiv is present, NO hosts are trusted

• The rhosts file is used to control access to an

individual user account

• It grant/denies password-free access to an individual

user account by means of rhosts

but rhosts does

 Everything SSH send across network is

encrypted SSH has become de-factor

standard for remote connection

 SSH can hanlde X connection

 Arbitrary TCP/IP ports can be redirect

through the encrypted channel in both directions

 For forwarding, ssh captures on port 6010

 Optional compression of all data with gzip

 Complete replacement for rlogin, rsh, rcp

authentication keys) ssh-agent Authetication agent, used to hold

RSA keys for authentication

agent make-ssh-known-hosts Used to create

/etc/ssh/ssh_known_hosts file

ssh-keygen2 The utility for generating keys

ssh-agent2 Authetication agent, used to hold

RSA keys for authentication

ssh-add2 Add identifier to the authentication

agent ssh-askpass2 X11 utility for querying password

 SSH has been 98% rewritten

 Supports other key-exchange methods

besides RSA : Diffie-Hellman key exchange

 Supports for DSA and other public key

algorithms besides RSA

 More secure and allows integration into

public key infrastrures

 Supports “subsystems”,

platform-independent module, built-in SOCKS, …

 Because of legal reasons, SSH is not included by default in Linux You can download and install from source code or from OpenSSH

 OpenSSH suite includes :

• ssh (replaces telnet and rlogin)

• scp (replaces rcp)

• sftp (replaces ftp)

 Client : openssh-clients-xxx.rpm

(ssh, ssh_config, sftp, )

 Addtion tools : openssh-xxx.rpm

(scp, ssh-keygen, )

as comment Keyword are case sensitive :

 All Linux distributions offer the wu-ftpd

program, which is ftp daemon developed at Washington University

 wu-ftpd is the most common daemon on

the Internet

 It’s main configuration file

class all real,guest,anonymous *

loginfails 5

message /welcome.msg login

message message cwd=*

compress yes all

tar yes all

chmod no guest,anonymous delete no anonymous

rename no anonymous

…

lp mail news uucp

…

 It’s another powerful ftp server, not popular

as wu-ftpd but easier to configure and more secure

 It can run as stand-alone server or from

inetd

 Relevant files :

/usr/sbin/in.proftpd : server daemon /etc/proftpd.conf : main configuration file