History  and  Features  of  Linux    

The  Unix   operating   system  was   imagined   and   implemented  by  Ken  Thompson  and  Dennis  Ritchie  (both  of  AT&T  Bell  Laboratories)  in  1969  and  first  released  in  1970.   Later   they   rewrote   it   in   a   new   programming   language,   C,   to   make   it  portable   work   in   different   computers   with   different   configuration.   The  availability   and   portability   of   Unix   caused   it   to   be  widely   adopted   copied   and  modified  by  academic  institutions  and  businesses.    In  1991,  in  Helsinki,  Linus  Torvalds  began  a  project  that  later  became  the  Linux  kernel.   He  wrote   the   program   specifically   for   the   hardware   he  was   using   and  independent  of  an  operating  system  because  he  wanted  to  use   the   functions  of  his  new  PC  with  an  80386  processor.    History  In   1980’s,   DOS   (Disk   Operation   System)   was   developed   by   Microsoft   and   the  dominated   Operating   System   for   Personal   Computers.   At   the   same   time,   MAC  Operating  System  was  developed  by  Apple  Computers.   It  was  better   than  DOS,  but   expensive   and   runs   only   Apple   configured   computers.   Parallally,   the   UNIX  Operating  System  was  also  available  at  the  same  time  and  was  much  better  than  DOS  and  MAC  OS.  But  much,  much  more  expensive  than  other  operating  systems.  So  people  were  really  looking  for  a  UNIX  based  system,  which  is  cheaper  and  can  run  on  PCs.  As  both  DOS,  MAC  and  UNIX  were  branded,   i.e.,   the  source  code  of  their   kernel   (OS)   is   protected   and   not   available   to   the   common   users.   So   no  modifications  to  the  above  Operating  Systems  are  possible  without  paying  high  license  fees.    In   1984,   Richard   Stallman,   who   believes   that   software   should   be   free   from  restrictions  against  copying  or  modification  in  order  to  make  better  and  efficient  computer  programs.  So  he  established  a  new  project  with  name  "GNU".  The  aim  of  GNU  was  to  develop  a  complete  Unix-­‐like  operating  system,  which  is  free  for  copying  and  modification.  The  companies  make  their  money  by  maintaining  and  distributing   the   software,   e.g.   optimally   packaging   the   software   with   different  tools   (Redhat,  Slackware,  Mandrake,  SuSE,  etc).  Richard  Stallman  built   the   first  free  GNU  C  Compiler  in  1991.  But  still,  an  OS  was  yet  to  be  developed.    Beginning  of  Linux  A   famous   professor   and   author   of  many   computer   books   Andrew   Tanenbaum  developed  an  operating  system  named  "Minix",  it  is  a  simplified  version  of  UNIX  operating   system   that   runs   on   Personal   Computers.   Minix   was   used   only   for  classroom   teachings   and  was  not   developed   for   commercial   use.   In   September  1991,   Linus   Torvalds,   a   second   year   student   of   Computer   Science   at   the  University   of   Helsinki,   developed   the   preliminary   kernel   of   Linux,   known   as  Linux   version   0.0.1.   And   then   onwards  many   companies   started   distributing  their  versions  of  Linux.    

Linux  Structure  

   Or    

   

File  System  of  Linux  In   a   Linux   system,   everything   is   a   file.   A   Linux   system   makes   no   difference  between  a  file  and  a  directory,  since  a  directory  is  just  a  file  containing  names  of  other  files.  Programs,  services,  texts,  images,  and  so  forth,  are  all  files.  Input  and  output  devices,  and  generally  all  devices,  are  considered  to  be  files,  according  to  the  system.    

Hardware  Requirements  of  Linux  o 700  MHz  processor  

o 512  MB  RAM  o 5  GB  of  hard-­‐drive  space  (or  USB  stick,  memory  card  or  external  drive)  o VGA  capable  of  1024x768  screen  resolution  o Either  a  CD/DVD  drive  or  a  USB  port  for  the  installer  media  o Internet  access  is  helpful  

 Linux  Kernel  

The   Linux   kernel   is   a   Unix-­‐like   operating   system   kernel   used   by   a   variety   of  operating   systems   based   on   it,   which   are   usually   in   the   form   of   Linux  distributions.   The   Linux   kernel   was   initially   imagined   and   created   in   1991   by  Finnish   computer   science   student   Linus   Torvalds.   Linux   rapidly   accumulated  developers   and   users.   The   Linux   kernel   has   received   contributions   from  thousands   of   programmers.   A   kernel   is   the   lowest   level   of   easily   replaceable  software   that   interfaces  with   the  hardware   in   your   computer.   It   is   responsible  for  interfacing  all  of  your  applications  that  are  running  in  “user  mode”  down  to  the   physical   hardware,   and   allowing   processes,   known   as   servers,   to   get  information   from   each   other   using   inter-­‐process   communication   (IPC).   There  are,  of  course,  different  ways  to  build  a  kernel  and  architectural  considerations  when  building  one   from  scratch.   In  general,  most  kernels   fall   into  one  of   three  types:  monolithic,  microkernel,  and  hybrid.  Linux  is  a  monolithic  kernel  while  OS  X  (XNU)  and  Windows  7  use  hybrid  kernels.    A  microkernel  takes  the  approach  of  only  managing  what  it  has  to:  CPU,  memory,  and  IPC.  The  advantages  of  microkernel  are  Portability  and  Security.  Monolithic  kernels  are  the  opposite  of  microkernels  because  they  encompass  the  CPU,   memory,   and   IPC,   but   they   also   include   things   like   device   drivers,   file  system   management,   and   system   server   calls.   The   advantages   of   Monolithic  kernels  are  more  direct  access  to  hardware  for  programs,  Easier  for  processes  to  communicate  between  each  other  etc.  Hybrid  kernels  have  the  ability  to  pick  and  choose  what  they  want  to  run  in  user  mode  and  what  they  want  to  run  in  supervisor  mode.  So  it  is  more  flexible  than  other  models.  

Linux  Commands  ls – List information about file(s) cat – Concatenate and print (display) the content of files cd – Change Directory chmod – Change access permissions clear – Clear terminal screen cp – Copy one or more files to another location rmdir – Remove folder(s) wc – Print byte, word, and line counts who – Print all usernames currently logged in grep – Search file(s) for lines that match a given pattern write – Send a message to another user mv – Move or rename files or directories find – Search for files that meet a desired criteria mkdir – Create new folder(s) more - Display output one screen at a time date – Display or change the date & time