Case Study 1: UNIX and LINUX - Beuth Hochschulepublic.beuth-hochschule.de/~rweis/.../AstUnix.pdf · 1 Case Study 1: UNIX and LINUX Aus: Andrew S. Tanenbaum, Modern Operation Systems

1

Case Study 1: UNIX and LINUX

Aus: Andrew S. Tanenbaum,Modern Operation Systems

History of unix Overview of unix Processes in unix The unix file system Security in unix

2

UNIX

The layers of a UNIX system.

UserInterface

3

UNIX Utility Programs

A few of the more common UNIX utility programs required by POSIX

4

UNIX Kernel

Approximate structure of generic UNIX kernel

5

Processes in UNIX

Process creation in UNIX.

6

POSIX

The signals required by POSIX.

7

System Calls for Process Management

s is an error codepid is a process IDresidual is the remaining time from the previous alarm

8

POSIX Shell

A highly simplified shell

9

The ls Command

Steps in executing the command ls type to the shell

10

Booting UNIX

The sequences of processes used to boot some systems

cp

11

The UNIX File System (1)

Some important directories found in most UNIX systems

12

The UNIX File System (2)

• Before linking.• After linking.

(a) Before linking. (b) After linking

13

The UNIX File System (3)

• Separate file systems• After mounting

(a) (b)

(a) Before mounting. (b) After mounting

14

System Calls for File Management

• s is an error code

• fd is a file descriptor

• position is a file offset

15

The lstat System Call

Fields returned by the lstat system call.

16

System Calls for Directory Management

• s is an error code

• dir identifies a directory stream

• dirent is a directory entry

17

UNIX File System (1)

Disk layout in classical UNIX systems

18

UNIX File System (2)

Directory entry fields.

Structure of the i-node

19

UNIX File System (3)

The relation between the file descriptor table, the open file description

20

UNIX File System (4)

• A BSD directory with three files• The same directory after the file voluminous

has been removed

21

The Linux File System

Layout of the Linux Ex2 file system.

22

Security in UNIX

Some examples of file protection modes

23

System Calls for File Protection

• s is an error code

• uid and gid are the UID and GID, respectively