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UNIX and LINUX

History of UNIX and Linux "Overview of Linux "Processes in Linux "Memory management in Linux "Input/output in Linux "The Linux file system "Security in Linux "

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UNIX

Multiuser, multiprogrammed"Rich libraries"Portable"POSIX

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History

1971. Unix Version 1, Ken Thompson"1973. ported to C"1979. AT&T Unix V7"1980. BSD 4.0"1983. AT&T - Unix System V"1985. BSD 4.3"1989. AT&T - Unix System V R4.0"1991. Linux 0.01 (9.3k lines C, 950 lines assembly)"

1994. Linux 2.0 (165k lines)

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Linux

The layers of a UNIX system.

UserInterface

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Utility Programs

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

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Kernel

Approximate structure of generic kernel

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Kernel

Approximate structure of Linux kernel

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Processes in UNIX

Process creation in UNIX.

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POSIX

The signals required by POSIX.

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System Calls for Process Management

s is an error code"pid is a process ID"residual is the remaining time from the previous alarm

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POSIX Shell

A highly simplified shell

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Threads in POSIX

The principal POSIX thread calls.

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The ls Command

Steps in executing the command ls type to the shell

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Flags for Linux clone

Bits in the sharing_flags bitmap

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UNIX Scheduler

The UNIX scheduler is based on a multilevel queue structure

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Linux Scheduler

• Real-time FIFO"• Real-time round robin"• Timesharing"

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Booting UNIX

The sequences of processes used to boot some systems

cp

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Handling Memory

• Process A's virtual address space"• Physical memory"• Process B's virtual address space

Process A Process B

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Sharing FilesTwo processes can share a mapped file.

A new file mapped simultaneously into two processes

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System Calls for Memory Management

• s is an error code"• b and addr are memory addresses"• len is a length"• prot controls protection"• flags are miscellaneous bits"• fd is a file descriptor"• offset is a file offset

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Paging in Linux (1)

Linux uses four-level page tables

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Paging in Linux (2)

Operation of the buddy algorithm.

Buddy algorithm

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Networking

Use of sockets for networking

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Terminal Management

The main POSIX calls for managing the terminal

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I/O (1)

Some of the fields of a typical cdevsw table

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I/O (2)

The Linux I/O system

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The UNIX File System (1)

Some important directories found in most UNIX systems

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The UNIX File System (2)

• Before linking."• After linking.

(a) Before linking. (b) After linking

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The UNIX File System (3)

• Separate file systems"• After mounting

(a) (b)

(a) Before mounting. (b) After mounting

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Locking Files

(a) File with one lock"(b) Addition of a second lock"(c) A third lock

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System Calls for File Management

• s is an error code"• fd is a file descriptor"• position is a file offset

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The lstat System Call

Fields returned by the lstat system call.

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System Calls for Directory Management

• s is an error code"• dir identifies a directory stream"• dirent is a directory entry

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File System

Disk layout in classical UNIX systems

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File System

Directory entry fields.

Structure of the i-node

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File System

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

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The Linux File System

Layout of the Linux Ex2 file system.

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File System

• A Linux directory with three files"• The same directory after the file voluminous has been

removed

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Network File System (1)

• Examples of remote mounted file systems"• Directories are shown as squares, files as circles

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Network File System (2)

The NFS layer structure.

The NFS layer structure

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Security in UNIX

Some examples of file protection modes

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System Calls for File Protection

• s is an error code"• uid and gid are the UID and GID, respectively