Introduction to Linux/Unix-I
Here we will see what these basic terms of Linux/Unix mean to us
Multi-user operating systems allow multiple users to
utilise the computer and run programs at the same time. All
are multi-user systems, but most batch processing systems for
mainframes were too, to avoid leaving the expensive CPU idle while it
waited for I/O operations to complete.
The most obvious example is a Unix server where multiple
remote users have access (via
Telnet) to the Unix shell prompt at
the same time.
In computing, multitasking is a method by which multiple tasks, also
known as processes, share common processing resources such as a CPU
with help of time slices. In the case of a computer with a single CPU,
only one task is said to be running at any
point in time, meaning that the CPU is actively executing instructions
for that task. Multitasking solves the problem by scheduling which task
may be the one running at any given time, and when another
waiting task gets a turn. The act of reassigning a CPU from one task to
another one is called a context switch.
Multiprocessing is traditionally known as the use of multiple
concurrent processes in a system as opposed to a single
process at any one instant. Like multitasking which
allows multiple processes to share a single CPU,
multiple CPUs may be used to execute multiple threads within a single
A Unix shell, also called “the command line”, provides the
traditional user interface for the Unix operating system. Users direct
the operation of the
computer by entering command input as text for a shell to execute
- Almquist shell (ash)
- Bourne shell (sh) Written by Steve Bourne, while at
Labs. First distributed with
Version 7 UNIX, circa 1978.
- Bourne-Again shell (bash)
- C shell (csh) Written by Bill Joy,
while at the University of
California, Berkeley. First distributed with BSD, circa 1979.
- scsh (Scheme Shell)
- TENEX C shell (tcsh)
- Korn shell (ksh) Written by Dave
while at Bell Labs.
- rc shell (rc) The Plan 9 shell by Tom Duff while at
Labs, later backported to Unix and other Operating Systems.
- Z shell (zsh)