Birmingham mumbai

teletypewriter
, which is a term used from a much different time period. In the past, a 
teletypewriter would be used to electronically send signals to a typing device on the 
other end of a wire. Obviously, we don't use machines like these nowadays, but the 
concept is similar from a virtual standpoint. On our server, we're using our keyboard 
to send input to a device that then displays output to another device. In our case, 
the input device is our keyboard and the output device is our screen, which is either 
connected directly to our server or is located on our computer which is connected to 
our server over a service such as SSH. On a Linux system, most processes run on a 
TTY, which is (to all intents and purposes) a terminal that grabs input and manages 
the output, similar to a teletypewriter in a virtual sense. A terminal is our method of 
interacting with our server.
In 
Figure 7.3
, we have two processes running on a TTY of 
tty1
, and the other 
processes are running on 
pts/0
. The TTY we see is the actual terminal device, and 
pts
 references a virtual (pseudo) terminal device. Our server is actually able to run 
several 
tty
 sessions, typically one to seven. Each of these can be running their own 
programs and processes. To understand this better, try pressing 
Ctrl
 + 
Alt
 + any 
function key, from 
F1
 through 
F7
 (if you have a physical keyboard plugged into a 
physical server). Each time, you should see your screen cleared and then moved to 
another terminal. Each of these terminals is independent of one another. Each of 
your function keys represents a specific TTY, so by pressing 
Ctrl
 + 
Alt
 + 
F6
, you're 
switching your display to TTY 6.
Essentially, you're switching from TTY 1 through to TTY 7, with each being able to 
contain their own running processes. If you run 
ps a
 again, you'll see any processes 
you start on those TTYs show up in the output as a 
tty
 session, such as 
tty2
 or 
tty4
. 
Processes that you start in a terminal emulator will be given a designation of 
pts
, 
because they're not running in an actual TTY, but rather a pseudo-TTY.

---

Chapter 7