CSC128: Introduction to UNIX

Communications


e-mail

mail (now we often use nail)
The command-line email program.  If you type mail by itself, it will either report that you have no messages and exit, or it will list your messages and prompt for further commands.
  • Entering just the message number will display that message to the screen.  
  • d(elete) [msg-number]  Deletes the message numbered [msg-number] .
  • r [msg-number]  Start composing a reply to [msg-number] .
 (nm)ail [-s subject] [username]
This will start composing an email to [username] .  The subject can optionally be specified on the commmand line.

To finish the email, type Ctrl-D or enter a dot (
. ) by itself on an otherwise empty line.  (Some versions of mail don't like Ctrl-D.)

Note that mail can be used like other UNIX commands.  The command:
ls -l | mail abear
This will send an e-mail to the user named abear , the contents of which are the output of the command ls -l .


pine
A nice, interactive email client, based on the pico editor.

There are many email clients, including graphically-based ones.



Using a Remote UNIX Machine
UNIX is multi-user.  All the machines in the CSC lab are networked together, and each has a name.  You can use any of the machines from any other one by using one
of the following commands.


rlogin [host]
This command will log you into the machine named [host] .

rsh [host] [command]
This command will execute [command] on the machine named [host] .  If [command] is ommitted, then acts the same as rlogin .


ssh [host] [command]
This is essentially the same as rsh , but it encrypts the communications, so that it is much more secure. I strongly suggest you get in the habit of using this command, and only use rsh when ssh isn't available on both your machine and the remote host.
See the man pages for ssh also see the man page for ssh-keygen. You use ssh-keygen to generate a key which is kept in $HOME/.ssh/identity , this is your private key and must be protected from being known by anyone but you. The public key, $HOME/.ssh/identity.pub is your public key and it can be copied to other hosts that you log into and placed into the file $HOME/.ssh/known_hosts . Now, if you do not specify a passphrase when you run ssh-keygen then copy the public key over to another systems known_hosts file, you can ssh from one machine to another securely without having to enter a password.


For more information on ssh and ssh-keygen see the page on ssh-keygen


Note: If you need to transfer files from a Windows host you use a utility such as WinSCP.

File Transfer using ftp and sftp



ftp
[host]
sftp [host]

(File Transfer Protocol ) This allows you to connect with a remote ftp host and send/receive files.  ftp  has its own command line; a few useful commands are listed below.  ( sftp is the ssh version of ftp;  use it if possible, although not all ftp servers will accept secure connections.)
ascii
binary
These commands switch between ascii and binary mode in ftp but not in sftp.  If you are transferring text files, use ascii mode; otherwise, use binary mode.
 

ls
ls -l (long listing)
cd [directory]
These commands do what you'd expect; they allow you to move around the remote filesystem and list the available files.  Be careful-- they behave a little differently than you might expect.

lcd [directory]
This command changes the local current working directory.

get [filename]
put [filename]
These commands do what their names suggest--
get
pulls the file named [filename] from the remote machine to the local machine.
put pushes the file named [filename] from the local machine to the remote machine.

user
Used to switch to another user if you are already logged in

open [hostname]
Used at the ftp prompt to open a connection to a machine. Often you may find that you are at a ftp prompt but have been dropped by the server, in which case you type open [hostname] which will re-connect you to the server.

mget
[filenames] ...
mput [filenames] ...
These are the same as get and put , but multiple filenames may be specified.

prompt

This command turns off the irritating habit of ftp to ask you to verify each file in an mget or an mput operation.  It also will turn it back on, if it's already off.

bye
The cute way of telling ftp that you want to close the session and exit.

rcp [user@host:filename] ... [user@host:filename ]


Usage: scp [source] [dest_file]

scp [user@host:filename] ... [user@host:filename]

This command also transfers files between computers, but uses a syntax similar to cp .
rcp
is unsecure; scp is more secure.



Multiple Users

who
Lists all users currently logged into the machine.

w
Also lists all users currently logged into the machine, but with different information.

finger[user@host]
Requests information about user.   Most systems now either ignore this (for historical security reasons), or simply don't keep the information updated.  This command is largely useless today.


Chatting
write [user@host] *
This command allows you to type lines of text that are then sent to the tty of user on the machine named host .  Use Ctrl-D to finish.  (*Note: in the Parkland UNIX lab, this only works for users logged into the same machine...)

ytalk
[user@host]
This command opens a two-way chat between yourself and user on the machine named host .  The specified user will be informed of the request to chat, and must then  run the talk command to you before chatting will begin.

ytalk

It is common now to use the more modern version of talk called ytalk which gives you access to multiple parties talking at once and the nice feature of being able to do shell commands inside of the ytalk session. The ESCAPE MENU in the ytalk man page has instructions on how to use the advanced features of ytalk for instance in a ytalk session ESC s takes you to a shell prompt within ytalk and typing exit will get you out of the shell and back into your normal "chat" mode of ytalk.


mesg
mesg y
mesg n
By iteself, this command reports on whether you are set to receive messages from writeor talk.   mesg y allows messages, and  mesg n denies messages.