Linux Administrationx

fullfattruckΚινητά – Ασύρματες Τεχνολογίες

10 Δεκ 2013 (πριν από 3 χρόνια και 5 μήνες)

60 εμφανίσεις








Linux Administration


1.

How deadlocks are handled in linux ?

2.

How many Logical ports are available in OS? eg.23 for Telnet like this what is total
number of available ports?

Ans.

An

operating system

(
OS
) is a set of

programs

that manage

computer hardware

resources
and
provide common services for

application software
. The operating system is the most important type
of

system software

in a computer system. A user cannot run an application program on the computer
without an operating system, unless the application program is self booting.

Time
-
sharing operating systems schedule tasks for efficient u
se of the system and may also include
accounting for cost allocation of processor time, mass storage, printing, and other resources.

For hardware functions such as input and output and

memory allocation
, the operating system acts as an
intermediary between application programs and the computer hardware,
[1]
[2]

although the application code
is usually executed directly by the hardware and will frequently call the OS or be interrupted by it.
Operating systems are found on almost any device that contains a
computer

from

cellula
phones

and

video game consoles

to

supercomputers

and

web servers
.

Examples of popular modern operating systems include

Android
,

iOS
,

Linux
,

Mac OS X
,

BSD
, all of which
have their roots in

Unix
, and

Microsoft Windows
.
[3]


3.

What is the main advantage of creating links to a file instead of copies of the file?

Ans.

In

computing
, a

symbolic link

(also

symlink

or

soft link
) is a special type of

file

that contains a
reference
to another file or directory in the form of an absolute or relative

path

and that affects pathname
resolution.
[1]

Symbolic links were already present by 1978 in mini
-
computer operating systems
from

DEC

and Data General's

RDOS
. Today they are supported by the

POSIX

operating
-
system
standard, most

Unix
-
like
operating systems

such as

FreeBSD
,

GNU/Linux
, and

Mac OS X
, and also
Windows operating systems such as

Windows Vista
,

Windows 7
and to some degree in

Windows
2000

and

Windows XP
.

Symbo
lic links operate transparently for most operations: programs which read or write to files named by
a symbolic link will behave as if operating directly on the target file. However, programs that need to
handle symbolic links specially (e.g., backup utilit
ies) may identify and manipulate them directly.

A symbolic link contains a text string that is automatically interpreted and followed by the operating
system as a path to another file or directory. This other file or directory is called the "target". The s
ymbolic
link is a second file that exists independently of its target. If a symbolic link is deleted, its target remains
unaffected. If a symbolic link points to a target, and sometime later that target is moved, renamed or
deleted, the symbolic link is no
t automatically updated or deleted, but continues to exist and still points to
the old target, now a non
-
existing location or file. Symbolic links pointing to moved or non
-
existing targets
are sometimes called

broken
,

orphaned
,

dead

or

dangling
.

Symbolic l
inks are different from

hard links
. Hard links do not normally point to directories, and they
cannot link paths on different

volumes

or
file systems
. Symbolic links may point to any file or directory
irrespective of the

volumes

on which the source and destination reside. Whereas hard links always refer
to an existing file, symbolic links may contain an arbitrary path that doesn't point t
o anything.

Some Unix as well as Linux distributions use symbolic links extensively in an effort to reorder the

file
system

hierarchy. This is accomplished with several mechanisms, s
uch as variant and context
-
dependent
symbolic links. This offers the opportunity to create a more intuitive or application
-
specific

directory
tree

and to reorganize the system
without having to redesign the core set of system functions and utilities.


4.

How to use Regular Expressions in QTP? give an example.

Ans.

HP QuickTest Professional

software provides functional and

regression test

automation for
software applications and environments.
[1]

Part of
the

HP

Quality Center tool suite, HP QuickTest
Professional can be used for enterprise quality assurance.
[2]

HP
QuickTest Professional supports keyword and scripting interfaces and features a graphical user
interface.
[3]

It uses the Visual Basic Scripti
ng Edition (
VBScript
) scripting language to specify a test
procedure, and to manipulate the objects and controls of the application under test.
[3]

HP QuickTest Professional was originally written by

Mercury Interactive
.
[4]

Mercury Interactive was
subsequently acquired by

Hewlett Packard

(HP) in 2006.
[5]

HP QuickTest Professional 11 is currently
available from

HP Software Divis
ion
.
[6]

HP QuickTest Professional is automated testing software designed
for testing various software applications and environments. It performs functional and

regression
testing

through a user interface such as a native GUI or web interface.
[7]

It works by identifying the objects
in the application user interface or a web page and performing desired operations (such as mouse clicks
or keyboard events); it can also capture object properties like name or handler ID. HP QuickTest
Professional uses a

VBScript scripting language to specify the test procedure and to manipulate the
objects and controls of the application under test. To perform more sophisticated actions, users may need
to manipulate the underlying

VBScript
.
[8]

Although HP QuickTest Professional is usually used for "UI Based"

Test Case

Automation, it also can
automate some "Non
-
UI" based Test Cases such as file system operations, database testing or Web
services testing.


5.

How you will uncompress the file?

6.

What command is used to display a list of currently running proc
esses?

7.

What is a login shell?

Ans.

A

Unix shell

is a

command
-
line interpreter

or

shell

that provides a traditional

user interface

for
the

Unix

operating system

and for

Unix
-
like

systems. Users direct the operation o
f the

computer

by
entering commands as text for a

command line interpreter

to execute or

by creating text scripts of one or
more such commands.

The most influential Unix shells have been the

Bourne shell

and the

C shell
. The Bourne shell, sh, was
written by

Stephen Bourne

at AT&T as the original Unix command line interpreter; it introduced the basic
features common to all the

Unix shells, including

piping
,

here documents
,

command
substitution
,

variables
,

control

structures

for condition
-
testing and looping and filename

wildcarding
. The
language, including the use of a reversed keyword to mark the end of a block, was influenced

by

ALGOL
68
.
[1]

The

C shell
, csh, was written by

Bill Joy

while a graduate student at

University of California, Berk
eley
. The
language, including the control structures and the expression grammar, was modeled on C. The C shell
also introduced a large number of features for interactive work, including
the

history

and

editing

mechanisms,

aliases
,

directory stacks
,

tilde notation
,

cdpath
,

job control

and

path
hashing
.

Both shells have been used as coding base and model for
many derivative and work
-
alike shells with
extended feature sets
.


8.

Explain Unix User security concept

Ans.

In this example, which is from the

chacl

command on the

Linux

operating system, the user

sue

is
granted

write

permission to the

/pvr
directory.

[
edit
]
User groups

Users under Unix

style operating systems often belong to managed groups with specific access
permissions. This enables users to be grouped by the level of access they have to this system. Many
Unix implementations add an additional layer of security by requiring that a us
er be a member of
the

wheel

user privileges group

in order to access the

su

command.
[1]

[
edit
]
Issues

Most Unix

and Unix
-
like systems have an account or group which enables a user to exact complete
control over the system, often known as a

root

account. If access to this account is gained by an
u
nwanted user, this results in a complete breach of the system. A root account however is necessary for
administrative purposes, and for the above security reasons the root account is

seldom

used for day to
day purposes (the

sudo

program is more commonly used), so usage of the root account can be more
closely monitored.

Root access "as it should be" can be visualised by those familiar with the

Superman

stories using the
following

analogy
:

Using a root account is rather like being Superman; an administrator's regular

user is more like
Clark Kent. Clark Kent becomes Superman for only as long as necessary, in order to save
people. He then reverts to his "disguise". Root access should be used in the same fashion. The
Clark Kent disguise doesn't really restrict him though
, as he is still able to use his super powers.
This is analogous to using the sudo program.