Unix – Linux

CS3353Ssystem Administration

OS

• The Operating System– Acts as the interface to all software, hardware,

and users of a computer.– Requires a file system for organizing files– Must maintain its viability to prevent other

programs, hardware, users, etc, from impeding its operation.

Unix and its variants will accomplish the above.

UNIX

• Consists of core software known as the kernel– The kernel acts to share resources of the system

with all running processes.– A process is a collection of resources associated

with a running program.

UNIX

• By 1973, it was a complete• Written using the C program language.– Multi user– Multi task– Multi processor

UNIX Variants

• There are many variants of UNIX. – BSD (1977)– AT&T System V (1983)– Linux (1991, Linus Torlvalds, Helsinki Finland)– Mac OS X is a UNIX based variant (1999).

UNIX

• Multi-user– The user accesses the computer in an

environment that is separated from other users sharing the computer’s resources.

– Access is through a verification process known as logging-in: Enter a user-id and password.

– The OS creates an environment known as the “shell” for the user after the login is complete.

The Unix/Linux Shell

• A command line interpreter• The shell is tagged with the user’s ID.• The user can have multiple independent shells

running simultaneously.

Shell Types

• sh = Bourne shell• csh = C-shell• ksh = korn shell, an enhanced c-shell.• bash = enhanced Bourne shell. The new

standard for shell scripting.

The UNIX-Linux OS

• The Unix/Linux OS consists of:– The kernel – the main controlling program that is

started at boot time.– Processes that support the kernel and all other

activity– The File system– Utilities