Operating systems unix

Operating systems unix

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  Presented by D.Achudhan. M.Sc Zoology Departmentof Animal Health And Management achukutty2612@gmail.com
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   Linux operating systemdeveloped by programming student Linus Torvalds  Linus wanted to develop Unix-like OS just to experiment with new 386 computer at the time...
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   What IsUNIX?  UNIX is an operating system which was first developed in the 1960s.  It is a stable, multi-user, multi-tasking system for servers, desktops and laptops.  UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no windows interface available, for example, in a telnet session.
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   The UNIXoperating system is made up of three parts;  the kernel, the shell and the programs.  The kernel of UNIX is the hub of the operating system:  it allocates time and memory to programs and handles the file store and communications in response to system calls.  The shell acts as an interface between the user and the kernel.
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   There aremany different versions of UNIX, although they share common similarities.  The most popular varieties of UNIX are Sun Solaris, GNU/Linux, and MacOS X.  The UNIX Operating System  The UNIX operating system is made up of three parts; the kernel, the shell and the programs.
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   A programminglanguage is an artificial language designed to express computations that will be executed on a computer.  Programming languages have a syntax (form) and semantics (meaning).  Java and C are example programming languages
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  7 • Unix Commands /home/larry# •That“something” is called a prompt. As its name would suggest, it is prompting you to enter a command. •Every unix command is a sequence of letters, numbers and characters. But there are no spaces. •When you first log into a unix system, you are presented with something that looks like the following:
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  8 Unix is alsocase-sensitive. This means that cat and Cat are different commands. The prompt is displayed by a special program called the shell. Shells accept commands, and run those commands. They can also be programmed in their own language. These programs are called “shell scripts”.
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  9  Unix providesfiles and directories.  A directory is like a folder: it contains pieces of paper, or files.  A large folder can even hold other folders-directories can be inside directories.  In unix, the collection of directories and files is called the file system. Initially, the file system consists of one directory, called the “root” directory  Inside “root” directory, there are more directories, and inside those directories are files and yet more directories. • Storing information
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   Each fileand each directory has a name.  A short name for a file could be joe,  while it’s “full name” would be /home/larry/joe. The full name is usually called the path.  The path can be divide into a sequence of directories. For example, here is how /home/larry/joe is read: /home/larry/joe The initial slash indicates the root directory. This signifies the directory called home. It is inside the root directory. The second slash corresponds to the directory larry, which is inside home. joe is inside larry.
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  11  A pathcould refer to either a directory or a filename, so joe could be either.  All the items before the short name must be directories. Root Directory Sub-Directory homeDirectoryDirectory larry joeFileFile Directory structure
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   ls listfiles and directories  ls -a list all files and directories  mkdir make a directory  cd directory change to named directory  cd change to home-directory  cd ~ change to home-directory  cd .. change to parent directory  pwd display current dir path
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   cp file1file2 copy file1 and call it file2  mv file1 file2 move or rename file1 to file2  rm file remove a file  rmdir directory remove a directory  cat file display a file  more file display a file a page at a time  who list users currently logged in  lpr -Pprinter psfile print postscript file to named printer  * match any number of characters  ? match one character  man command read the online manual page for a command
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   command >file redirect standard output to a file  command >> file append standard output to a file  command < file redirect standard input from a file  grep 'keyword' file search a file for keywords % grep science science.txt  wc file count number of lines/words/characters in file % wc -w science.txt  sort sort data (numerically or alphabetically) Ex: to sort the list of object, type % sort < biglist and the sorted list will be output to the screen.
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  TIME User 1 User 2 User3 User 4 User 5 User 6 User 7 User 8
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   The UnixOS is a multi-user OS allowing more that more person to directly communicate with the computer.  Although the OS can only work on one task at a time, a small piece of time (time slice) is dedicated to each task or user - this is referred to as “time-sharing”.  Time sharing gives the illusion that the CPU is giving all the users its full attention