Introduction to Unix \ Linux


Unix \ Linux Introduction for Begineers

What is UNIX?

  • Unix is an Operating System
  • It is truly the base of all Operating Systems 
  • Sub-products of Unix are Linux, Ubuntu, Solaris, POSIX, etc. 
  • It was developed in the 1970s by Ken Thompson, Dennis Ritchie, and others in the AT&T Laboratories. 
  • It was originally meant for programmers developing software rather than non-programmers. 

Commercial implementations of UNIX in late 80’s

  • Hewlett Packard’s HP-UX 
  • IBM’s AIX 
  • Lynx’s Real-Time UNIX
  • NeXT’s NeXTStep 
  • Santa Cruz Operation’s SCO UNIX 
  • Silicon Graphics’ IRIX  
  • SUN Microsystems’ 
  • SUN OS and Solaris and dozens more.

Architecture is divided into three levels.

  • The lowest level is the kernel , which schedules tasks , manages resources, and controls security. 
  • The next level is the shell, which acts as the user interface, interpreting user commands and starting applications. 
  • The highest level is utilities, which provides utility functions. It is called as USER level.

UNIX File System - Hierarchy

  • /: This is top level directory    It is parent directory for all other directories    It is called as ROOT directory    It is represented by forward slash (/)    C:\ of windows     
  • /root: it is home directory for root user (super user)    It provides working environment for root user    C:\Documents and Settings\Administrator  
  • /home: It is home directory for other users      It provide working environment for other users (other than root)    c:\Documents and Settings\username    
  • /boot: It contains bootable files for Linux    Like vmlinuz (kernel)..... ntoskrnl    Initrd (INITial Ram Disk)and    GRUB (GRand Unified Boot loader)....  boot.ini, ntldr  
  • /etc: It contains all configuration files    Like /etc/passwd.....  User info     
    • /etc/resolv.conf... Preferred DNS     
    • /etc/dhcpd.conf.... DHCP server    C:\windows\system32\dirvers\/usr By default soft wares are installed in /usr directory    (UNIX Sharable Resources)    c:\program files  
  •  /opt: It is optional directory for /usr    It contains third party softwares    c:\program files  
  •  /bin: it contains commands used by all users    (Binary files)  
  •  /sbin: it contains commands used by only Super User (root) 
  • /dev: it contains device files    Like  /dev/hda  ... for hard disk    /dev/cd rom ... for cd rom    Similar to device manager of windows  
  • /proc: it contain process files    Its contents are not permanent, they keep changing    It is also called as Virtual Directory    Its file contain useful information used by OS    like /proc/meminfo ... information of RAM/SWAP    /proc/cpuinfo ... information of CPU 
  • /var: it is containing variable data like mails, log files     /mnt  it is default mount point for any partition    It is empty by default  
  • /media: It contains all of removable media like CD-ROM, pen drive 
  • /lib: It contains library files which are used by OS    It is similar to dll files of windows    Library files in Linux are SO (shared object) files     

Linux Commands:

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