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System Software
Roman Prykhodchenkorprikhodchenko@kture.kharkov.ua
Unix basics
Tuesday, February 8, 2011
Agenda
• History
• Terminology
• Unix commons
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History
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UNIX
• UNIX is a computer operating system originally developed in 1969 by a group of AT&T employees at Bell Labs.
• Today UNIX is a family of the operating systems that correspond to the Single Unix Specification.
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Main events
• 1969 – MULTICS, the first implementation of the UNIX operating system for General Electric GE-645 computer.
• 1976 – UNIX Timesharing System 6
• 1977 – Berkley Software Distribution (BSD)
• 1979 – UNIX Timesharing System 7
• 1982 – BSD 4.1 implements TCP/IP
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PeopleDenis Ritchie Brian Kernighan Ken Thompson
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Main events
• 1988 – First edition of POSIX standard
• 1989 – The ANSI C standard is published
• 1983 – Richard Stallman initiated the GNU project
• 1992 – The GNU is using the Linux kernel
• 1994 – 386 BSD is released
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PeopleLinus Torvalds Richard Stallman
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People
William Jolitz Lynne Jolitz
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Terminology
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*nix
• UNIX-like operating system (or just *nix) is an operating system that behaves similar to UNIX but does not correspond to the Single Unix Specification.
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SUS
• Single UNIX specification is the collective name of a family of standards for computer operating systems to qualify for the name "Unix"
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POSIX
• POSIX (Portable Operating System Interface for uniX)is the standard for the UNIX operating system published by IEEE Computer Society.
• Includes:
• System API
• Shell interface
• API of the system utilities
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Time-sharing
• Time-sharing operating system shares a computing resource among many users by means of multiprogramming and multi-tasking.
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Unix commons
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Key properties
• Portability
• Preemptive multitasking
• Virtual memory
• Multilevel architecture
• Support of asynchronous processes
• Device-independent I/O
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Software conception
• Do only one thing and do it well.For each task the system can perform there is a separate program.
• Examples:cp – copies a filecat – prints a file’s contents
• Benefits:- Simplicity- Number of errors is relatively small.
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Everything is a file
• Every computer’s resource is represented by a file.
• Examples:/home/john/text.txt – John’s text file/dev/sda – first hard drive/proc/scsi – information about any devices connected via a SCSI or RAID controller
• Benefits:Device-independent I/O operations.
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Multilevel architecture
• Each software type runs on an appropriate level
• Memory is not shared between different levels
• System calls for inter-level communications
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Multilevel architecture
Application software, network services, utilities
System software (command interpreters, protocols...)
System calls
Kernel
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Kernel
• Scheduling
• Memory management
• Interruptions processing
• Inter-process communication
• Low-level device support
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Kernel
• Monolithic kernel
• Microkernel
• Nanokernel
• Exokernel
• Hybrid kernel
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Kernel
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Kernel“Exokernel”
based Operating System
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System calls
• Process management
• Implementation of I/O operations
• Bind user actions to drivers
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Signals
• Signals are an approach of inter-process communication (IPC)
• Signal is an asynchronous message sent to signal
• Operating system interrupts the process when it is sent a signal
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Signals
• A process can implement a handler for different kind of signals
• Default handler kills the process
• Some signals can not be handled
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Signals
• Sources of signals:
• Keyboard shortcuts
• Kernel
• Hardware exception
• Wrong system call
• I/O operations
• A process
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ShellShell is a command-line interpreter that provides a traditional user interface for the Unix operating system and for Unix-like systems.
Most popular are: bash, sh, csh, zsh
We will mostly use bash.
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Common syntax$ app_name [options] [parameters]
Options begin with - or --
-o1 [value] -o2 -o3 [value]
or-o1o2o3
Examples:$ tar -x -j -v -f archive.tar.gz$ tar -xjvf archive.tar.gz
Parameters are usually required.$ rdesktop -f -u UserName 192.168.0.124
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Manual pagesMan application shows a manual page for specified application:
$ man {app_name}
Or you can use option -h to see a short help:$ tar -h
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File system hierarchy standard/ Rood directory
/bin/ Essential command binaries
/boot/ Static bootloader
/dev/ Devices represented by files
/etc/ Host-specific configuration data
/lib/ Basic shared libraries and kernel modules
/mnt/ Temporary mount point
/opt/ Optional software
/sbin/ Basic system software
/tmp/ Temporary data
/usr/ Secondary hierarchy
/var/ Variable data
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PATHPATH is an environment variable used by shells for searching for applications.
Applications located in directories that are included to PATH can be launched without specifying full path.
$ echo $PATH/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/X11R6/bin
You can modify PATH$ PATH=$PATH:~/bin
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Navigationcd Navigates to specified directory
ls Shows current directory’s contents
pwd Shows current directory
mkdir Creates a directory
rmdir Removes a directory
touch Modifies last change date
rm Deletes a file
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InodesInode is an index descriptor of a filesystem resource.
- Every resource has own inode number.- File name is a link to inode.
Example:$ ls -dl /usr/localdrwxr-xr-x 8 root root 240 Dec 22
/usr/local/usr/local/./usr/local/bin/../usr/local/games/../usr/local/lib/../usr/local/sbin/../usr/local/share/../usr/local/src/..
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Questions?
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