User

Question 1

what are two ways a user can interact with the OS

Answer 1

command line
- shell, unix, errors, paths, pipes, links, setuid
programming interface
- dynamic memory allocation, locks, errors, shared memory

Question 2

what is a filing system

Answer 2

The filing system lives between the user applications – which want to handle files and the device drivers which move blocks of data to and fro

Question 3

what does the file store (filing system) provide and allow for

Answer 3

it provides a large, persistent storage mechanism that allows for

• IPC
• access rights

Question 4

describe how virtual devices are represented in windows vs unix

Answer 4

windows: each device has own tree
unix: branches off one tree

Question 5

what is a file

Answer 5

basic unit of storage in a filing system

Question 6

files are….

Answer 6

large
slow to access
permanent

Question 7

what makes up a file

Answer 7

attributes and blocks

Question 8

How does a filing system access a file from a file name

Answer 8

each file has a filename that is abstracted to a handle which leads to a descriptor

Question 9

how do we open a file

Answer 9

system call to fetch

Question 10

how do we close a file

Answer 10

push any buffered data to the file

Question 11

how do we perform read/write, why

Answer 11

in blocks

to limit the number of system calls

Question 12

how do we perform seek on a file

Answer 12

it is costly, we treat the file as an array to allow for random access

Question 13

what is a memory mapped file

Answer 13

makes the file appear in a process’ virtual memory space

Question 14

what is file locking

Answer 14

placing a lock on a file prevents against race hazards. only one process can access it

Question 15

what is a volume

Answer 15

a logical drive

corresponds to a disk partition

Question 16

when is moving a file easy, when is it complicated

Answer 16

moving files within a volume is simple

moving files between volumes is difficult

Question 17

what are two file system implementation schemes

Answer 17

FAT and Inodes

Question 18

describe a file allocation table

Answer 18

have an array of cluster pointers.

the FAT table is a linked list

a directory gives a pointer to the start of a file

fragmentation is common

Question 19

what is a cluster

Answer 19

set of data blocks

Question 20

where is FAT most common, what about inodes?

Answer 20

fat in windows

inodes in unix

Question 21

describe inodes

Answer 21

a structure that contains file attributes and an array of pointers to blocks.

small and kept in memory only when file is in use

files are identified by inode number

Question 22

how many blocks of an inode point to other blocks

Answer 22

blocks 1-9 for small files
then a pointer that points to 10-17
next pointer, then pointer 18-81
finally, 82-593

Question 23

describe links

Answer 23

used to copy a file without duplicating data

Question 24

what is a symbolic link

Answer 24

a soft link, a pointer to the file

Question 25

what is a hard link

Answer 25

directory entry contains the inode number.

the file is the link

Question 26

what is a file descriptor

Answer 26

created when a file is opened

access permissions, current position, error status, control flags

Question 27

what is a library

Answer 27

a collection of code for common functions

Question 28

describe a static library

Answer 28

linked at compile time

Question 29

describe a dynamic library and its advantages

Answer 29

library code is not linked or included in the application

this saves space, is easier to maintain, and doesn’t need to be recompiled when it is changed

Question 30

what must a shared library be

Answer 30

re-entrant, relocatable, linked dynamically

Question 31

what is a shell

Answer 31

a user interface program that allows the user to give commands to the computer

Question 32

what is bash

Answer 32

allows us to launch programs with arguments and set up pipes

Question 33

what do shells allow

Answer 33

scripting and aliases

Question 34

what are environment variables

Answer 34

they belong to the environment of a process. maps names to values.

Question 35

how do we access environment variables in a shell

Answer 35

$

Question 36

what happens to environment variables when a process forks, what can we do to change this

Answer 36

the child does not inherit the environment variables.

export

Question 37

give some examples of environment variables

Answer 37

path

home

shell

random

manpath

Question 38

what is man

Answer 38

manual page reader in unix

Question 39

describe a file system

Answer 39

a usb will have its own file system, this will be different to that of the hard disk

they appear as separate devices

but files can easily be transferred back and forth

Question 40

what do we find within each block group on a disk partition

Answer 40

The superblock and group descriptor: specify details like the size of the group, the number of i-node entries, the start of the free-block list.

bitmaps- indicate whether a data block/i-node is used or not.

i-node table- array of records which defines both the file (data blocks) and its attributes.

Question 41

what is a directory

Answer 41

A file which contains a linked list of entries. File-names vary in length so space is allocated (and deallocated) in much the same way as RAM

Question 42

where is the filing system in a monolithic vs microkernel

Answer 42

In a ‘layered’ model the filing system is quite a high-level O.S. layer.

In a microkernel it may well be run (by the O.S.) in user mode.