Commands covered in this section: rlogin telnet sz rz ping finger who rwho talk write mesg
Logging into Remote Computers
There are times when you will need to log into a remote computer
to do this there are several commands available on the UNIX systems.
Use rlogin hostname to log into the computer called hostname.
You will be accessing that computer as if it was the machine you are using, this means that
your environment settings will be effective for that rlogin (the shell that account is
set-up with will be operational, so if you are using zsh and that account is set to use bash on
login you will be using the bash shell).
On occasions the need may arise for you to log into a remote host using another userid. to do
this use rlogin -l userid hostname. This will allow you to log into hostname under a different identity,
which will remain effective during that session.
Note: Some UNIX systems inverse the order of the hostname and userid so if the example
given above does not work use rlogin hostname -l userid.
You will need to have a password for the account you are trying to log into or have permission to use it without a
password.
Using Telnet
Telnet is a well known internet utility and as such it is available on most systems, the most important difference
between rlogin and telnet is that you cannot use
rlogin with PC based networks, it will only work on
UNIX networks. To access PC networks use telnet
Type telnet hostname to connect directly to the machine specified by hostname, if you want to
connect to a specific port type telnet hosname port (note, space required). The hostname
can be either a full name such as crocus.csv.warwick.ac.uk or it can be a simple IP address as 128.83.165.133
If you just type telnet without supplying a hostname you will get the telnet prompt
which looks as this: telnet>
at this prompt you can use any of the telnet commands
described bellow.
Note: To use any of these command s you will need to be at the telnet prompt, if you are in a telnet session
to escape use Ctl & ] to get to the prompt (you connection to the remote computer will not be lost).
| Command | Short Format | Parameters | Action |
| open | o | hostname (port) | Opens a new telnet connection to remote computer |
| close | c | none | Closes your current connection to remote computer and returns you to the telnet prompt |
| quit | q | none | As close but exits from the telnet utility completely. |
| status | st | none | Displays telnet status |
Advanced Telnet Use
Telnet provides may option allowing you to make more advanced use of the networking facilities offered by
UNIX, we will here describe a few of the most commonly used.
z allows you to either suspend telnet and return to your shell or to start a subshell, this will mostly depend
on your system set-up, but the end result will be practically the same, you will be working in your sub/shell while the
remote connection is suspended. On most UNIX systems this means that you will be able to use rz or
sz to receive (or send)
files via the Zmodem transfer protocol.(see bellow)
m or mode Will allow you to change the modes of transmission between the two computers. This will effect the
speed of transfer as well as the way the data is transferred(note: both computers need to support these option for
mode to work, try it, if it starts complaining, it doesn't support that mode!).
- mode c will cause transmission to be in the character form, so that each character you type at your terminal
will be immediately transferred to the remote computer. This mode is very efficient when you are telneting to a
computer located on the same network as your own, or one that is very close. if you are communicating with a computer that
is far use the next mode.
- mode l sets the communication to be in line mode. This will cause telnet to wait until you have pressed ENTER before transmitting, and
it will then transmit the whole of your line. This is faster as all your data is sent in as little data packets as possible.
sz amp rz
These two utilities are used in conjunction to telnet to send and receive files using the Zmodem Protocol.
Use the z telnet command as described above, then type
binary on to switch from ASCII transfer to binary transfer, start the rz in the background by
typing bg rz. This will cause the system
to wait for a Zmodem transfer. Then bring the telnet session back to the foreground (see section on Controlling Processes for details on
how to use fg bg, ...) and start the sending the file in Zmodem.
Because of the wonders of the Zmodem Protocol all the necessary setting will be in set-up by the two computers and the file transmitted, once the rz
job is finished your file will be received. To send a file use the same procedure but type bg sz filename, and instruct the remote computer to
receive the file.
Computer Status
Telnet connections refused? Unable to rlogin? The computer you are
trying to access might be down. To find out if it is the remote computer
or your utility type ping hostname
. This give you either
hostname is alive or hostname is not responding (some say
dead!).
If when you type ping hostname you get no response for a long
time, then the remote computer is either dead or remote connections have
been disabled. Try later!
Finding all about a Remote User
There are time, when we need to (or would like to) know as much as
possible about a given user. To do so use finger userid
This will give you something like:
[localhost]
Login name: lauvj
In real life: Mr F Blaskovic
Directory: /home/crocus8/la/uvj
Shell: /usr/local/bin/zsh
Mr F Blaskovic (lauvj) is not presently logged in.
Last seen at crocus on Sun Aug 18 12:39:05 1996 from somewhere.com
Mail forwarded to someplace.on.the.net
This is the long version of the output given by finger. (which is
usually the default on localhosts). If it isn't the default use finger -
l userid, or if it is the default and you want the short format use
finger -s userid.
If you have a file called .plan or .project, those will be displayed.
Note in the above example there is a reference to main being forwarded
followed by the address to where the mail is forwarded. This will be
displayed if the user has a .forward file in their home directory.
If you don't want to wait for finger to display the .plan, .project or
.forward files use finger -p userid.
Use finger -options userid@hostname to find a user at hostname, or any
user that matches the string userid. If you are on a network with
several hosts instead of using finger userid, use
finger -options
userid@ this will search all your LAN hosts machines. Use finger
-options @hostname to get a listing of all users on hostname
Finding Users with who
To find out about users, processes on your machine use who. who will
display a list of users in this format:
| root | -tty03 | Aug 20 03:42 |
| frankie | +tty01 | Aug 20 10:22 |
| matt | +tty20 | Aug 20 19:03 |
| ops | -tty00 | Aug 20 00:00 |
As show the output will include the login name of the users, the tty,
date and time. If you use who -T, before the tty a + or - will be
displayed (as above), this indicates whether you can write to the
terminal or not (a + means that you can write to the terminals and - you
can't). The who -m will show you the equivalent of the who am i command,
all the information you need about yourself.
Another useful option to who is -H which will put a header above each
column of the output.
who for Remote Users
The who command can be used in the same way as you would use who, but
will display information about remote users instead of local ones.
Use rwho hostname, to get a list of all users logged in at
hostname. To get a listing as that which is produced by who,
type rwho -l hostname. And a useful switch is -a which will
produce a report on the specified machine even if no users are logged
in.
Talking to Other Users
If you need to talk to another user use talk.
First you will need to know at what machine the
person you want to talk to is logged on (use finger, rusers, ... to find out).
Type talk userid@hostname where userid is the login name of the person you want to talk to
and hostname is the machine where s/he is logged on (don't forget the @ sign!).
If the person you want to talk to is still logged in s/he will get a
message that looks like:
Message from Talk_Daemon@darkstar at 16:00 ...
talk: connection requested by user@darkstar.
talk: respond with: talk user@darkstar
To respond you would type talk user@darkstar, your screen will then split in two. All you type will appear in the top half
and what the person talking with you type will appear on the bottom part.
You will quickly notice that your screen becomes a mess, to clear it use Ctl & L. To quit from the talk
connection use Ctl & C. This
will terminate the talk session and return you to your shell.
Using Talk Across Networks
To use talk across networks you need to know the machine name as well as the hostname for the person whom you want to talk with.
Best way to find that out is to ask them! Alternatively use finger.
type talk userid@machinename.hostname, for example you would use lauvj@crocus.warwick.ac.uk to
get in touch with me. Notice how you put the user name followed
by the @ sign, the name of the machine (crocus), and then the hostname (here warwick.ac.uk).
Using Write
To just write a message on another user's screen use write userid or optionally
write userid ttynn, where nn is the tty number the user is using. After you typed in the command type in any text/messages you wish to send.
then end it with a Ctl & C.
That person will then receive something like:
Message from yourid yourtty
The message you typed in.
Stopping Messages
Some times you just don't want other people disturbing your work, and having talk
requests and messages popping up all over the place can be very disturbing.
To stop any messages use chmod -w /dev/tty or you can use
mesg n. This will
prevent you from being disturbed by the talk/write messages.
Note: These commands won't stop any messages from the superuser, the only way
you can stop these is, not being logged on!
Frankie Blaskovic
Last modified: Sun Aug 10 15:18:02 BST 1997
