COMP 252 Operating Systems

1
COMP 252Operating Systems

• Lab 01

2
Welcome

• About Me
• Yiyang Zhao (???)
• Website http//www.cse.ust.hk/zhaoyy
• Office 4205
• Hobbies basketball, swimming
• About Lab Tutorials
• 3 parts
• Review
• Nachos
• Practice

3
Outline

• Review Questions
• UNIX basics and Vi editor
• Using SSH to remote access Lab2(4214)
• Compiling a C Program
• Makefile
• Basic C/C programming
• Process Control example on fork()
• (Optional) GDB text base debugger

4
Review

• Review Questions
• (PPT)http//course.cs.ust.hk/comp252/web08fall/Lab
  1/lab01_review.ppt
• (PDF) http//course.cs.ust.hk/comp252/web08fall/La
  b1/lab01_review.pdf
• http//course.cs.ust.hk/comp252/web08fall/Lab1/lab
  01_review_sol.pdf

5
UNIX basic

• Basic command
• ls
• ls a show hidden files or directories
• ls l list in long listing format
• ls al
• cd
• cd / cd change to home directory
• mkdir, rmdir, mv
• rm
• rm r directory remove the contents of
  directories recursively
• rm f file remove file without prompt
• cp copy a file

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UNIX basic

• Practice
• Create a comp252 directory for lab1 under home
  directory
• cd
• mkdir comp252
• cd comp252
• mkdir lab01
• cd lab01
• Copy a file from comp252 directory
• cp /course/comp252/web08fall/Lab1/Makefile/numprin
  t.c .
• cp /course/comp252/web08fall/Lab1/Makefile/main.h
  .
• cp /course/comp252/web08fall/Lab1/Makefile/main.c
  .

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UNIX basic

• Cat
• cat filename display content of a file
• cat gt filename create and append content to a
  file
• cat gtgt filename append content at the end of
  a file
• Practice
• cat main.c // show you the content of main.c
• cat gt helloworld.txt (enter)
• type Hello World (Enter) (Ctrl D)
• cat helloworld.txt

8
UNIX basic

• Get help information to see how to use UNIX
  command
• rm --help
• cp --help more
• cat --help
• find command
• search for files in a directory hierarchy
• try find --help more
• Search main.c file in your home directory
• find . -name main.c

9
UNIX basic

• Useful links
• http//course.cse.ust.hk/comp252/web08fall/Referen
  ce.html

10
Vi Starting vi

• You can use editors under X-windows like kate,
  you can also use a text base editor like Vi
• Starting vi
• vi filename Start at line 1 of file
• vi n filename start at line n of file
• vi filename start at last line of file
• vi r filename recover file after a system
  crash
• Two modes in vi
• Insertion mode press i or I enter this mode
• Command mode press Esc enter this mode

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Vi saving files and leaving vi

• Saving files
• e filename save current and edit other file
• w save current editing file
• w filename save as file
• w! filename save as existing file
• Leaving vi
• q quit vi
• wq save file and quit vi
• q! quit vi without saving
• Copy yy
• Paste p
• Cut cc

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Vi commands

• Moving cursor
• Inserting text
• Changing and replacing text
• Deleting text
• Markers
• Search and replace
• (Go to here)
• http//course.cse.ust.hk/comp252/web08fall/Others/
  vi-ref.pdf

13
Vi Practice

• Practice
• Open helloworld.txt
• vi helloworld.txt (In command mode at the
  beginning)
• (press i to enter insertion mode, you can edit
  the file now)
• (press Esc to enter command mode)
• (press dd to delete current line)
• (press ndd to delete n line below current line)
• (press wq in command mode to leave vi and
  save the file)

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Remote access Lab2(4214)

• Software
• SSH secure Shell
• http//www.ssh.com
• http//cssystem.cse.ust.hk/home.php?docbaseUGuide
  s/RemoteAccessreq_urlUGuides/RemoteAccess/ssh.ht
  ml
• Putty
• http//www.putty.nl
• UNIX ssh command
• ssh l username hostname
• eg. ssh l lfxad csl2wk35.cse.ust.hk

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How to use SSH secure shell

• After you install SSH and start it, click Quick
  Connect

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Logging Page

• Host Name csl2wkXX.cse.ust.hk
• XX can be 01 to 40
• User Name your CSD logging account
• Port Number 22 (SSH default port)
• Authentication method Password

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First time logging to a machine

• Press Yes to save a host key
• If you save it in your local computer, this
  windows will not popup when you logging to same
  machine again

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Enter your password

• Enter your password and click OK

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You logging to a machine!!!
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Notes

• A machine can be accessed for more than one user
  at the same time, use who command to know who
  is using the machine
• You can click Window -gt New Terminal to start
  another terminal to the same machine
• SSH secure Shell is available in the CS lab 1,
  lab 3, lab 4 and all computer bran.

21
Compiling a C Program

• GNUs C Compiler (gcc)
• The main compiler that will be used in this
  course
• For compiling C programs, you can use g
• Linux/UNIX does not have a pretty program like
  Microsoft Visual Studio for managing C
  programming projects
• Compiling a C program
• gcc g m32 ansi Wall c main.c o main.o
• gcc g m32 ansi Wall c numprint.c o
  numprint.o
• -g include symbols for gdb debugger.
• -m32 compile and link 32bit i386 binaries
• -ansi check code against ansi C standard.
• -Wall display all warnings.
• Use ansi and -Wall for user programs.
• Use Wall for kernel programs.
• Linking
• gcc g m32 ansi Wall main.o numprint.o o
  lab01

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Makefile

• You need to type quite a bit for compiling a
  simple program
• For large projects
• You may have many .c and .h files
• You may use many library calls
• You need to specify them at compilation time.
• Things start to get tedious and messy
• One way to manage this complexity is to use a
  Makefile
• Automates the compilation process
• Easy to declare all the compilation options and
  flags

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Makefile

• Example Makefile
• SRCS main.c numprint.c
• HDRS main.h
• OBJECTS main.o numprint.o
• INCLUDE -I/usr/local/include
• LIBS -lm
• CC gcc
• CFLAGS -g ansi Wall
• EXEC lab01
• all (EXEC)
• (EXEC) (OBJECTS)
• (CC) (FLAGS) (INCLUDE) (LIBS) (OBJECTS) o
  (EXEC)
• clean
• rm f (OBJECTS) (EXEC) core
• depend
• makedepend -- (CFLAGS) (INCLUDES) (SRCS)
  (HDRS)
• DO NOT DELETE THIS LINE make depend depends
  on it.

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Makefile

• The first few lines are fairly straightforward
• SRCS, HDRS, and OBJECTS specify the source,
  header, and object files
• INCLUDE, the directory for include files
• LIBS, the library to be linked into the
  compilation
• CC, the type of C compiler
• CFLAGS, the compilation flags
• EXEC, the name of the executable image.
• The line containing all specifies the final
  compilation targets
• in this case, the content of EXEC, or (EXEC).
• The creation of (EXEC) depends on the
  (OBJECTS), or object files.
• To create (EXEC), the compiler needs to link the
  objects by running the (CC) command.
• All the .c files are automatically converted to
  .o files without the need of specifications.
• Note that you need to tab the indentation of the
  (CC) command. Makefile wont work if you use
  the space bar to create the indentation.
• Lines start with denote comments. Lets ignore
  the remaining lines for now. With this Makefile
  in your current project directory, all you need
  to type to compile your project is gmake.

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Makefile

• Prepare a Makefile (can be found on course web)
• cp /course/comp252/web08fall/Lab1/Makefile/Makefil
  e .
• cp /course/comp252/web08fall/Lab1/Makefile/numprin
  t.c .
• cp /course/comp252/web08fall/Lab1/Makefile/main.h
  .
• cp /course/comp252/web08fall/Lab1/Makefile/main.c
  .
• cat Makefile
• Run the Makefile
• gmake
• More about Makefile
• http//users.actcom.co.il/choo/lupg/tutorials/wri
  ting-makefiles/writing-makefiles.html
• http//www.gnu.org/software/make/manual/html_node/
  index.html

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Basic C/C programming

• Please read a C tutorial on our course web
• http//course.cs.ust.hk/comp252/web08fall/Lab1/C2
  0basics/c_tutorial.pdf
• And write a HelloWorld C program
• Understand command line arguments in C/C
  program
• http//course.cs.ust.hk/comp252/web08fall/Lab1/C2
  0basics/command-line_color.pdf
• And run ./lab01 h n 5

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Basic C/C programming

• Read and understand the source code that we just
  compiled
• main.h, main.c, numprint.c
• Run ./lab01 h n 5
• A quick introduction to C
• http//course.cs.ust.hk/comp252/web08fall/Lab1/C2
  0basics/c.pdf
• Useful Links
• http//course.cs.ust.hk/comp252/web08fall/Referenc
  e.html

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Process control

• When UNIX runs a process, it gives each process a
  unique number called process ID, pid.
• may be a "system'' program (e.g., login, csh)
• or program initiated by the user (e.g., textedit,
  dbxtool or a user written one).

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Process control

• The UNIX command "ps" will list all current
  processes running on your machine with their pid.
  
• The C function int getpid() will return the
  process id of process that called this function.

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fork() create a new process

• The fork() system call will spawn a new child
  process which is an identical process to the
  parent except that has a new system process ID.
• The process is copied in memory from the parent
  and a new process structure is assigned by the
  kernel.

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fork() create a new process

• Synopsis
• include ltsys/types.hgtinclude ltunistd.hgt
• pid_t fork(void)

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fork() create a new process
child
parent
Program code
Program code
Data
Data
Heap
Heap
Stack
Stack
33
fork() create a new process
child
invoke fork()
parent
Program code
Program code
Data
Data
Heap
Heap
Stack
Stack
34
fork() create a new process
child
invoke fork()
parent
Program code
Program code
Data
Data
Heap
Heap
Stack
Stack
35
fork() create a new process
child
invoke fork()
parent
Program code
Program code
Data
Data
Heap
Heap
Stack
Stack
36
fork() create a new process
a new process structure is assigned by the kernel
child
invoke fork()
parent
Program code
Program code
Data
Data
Heap
Heap
Stack
Stack
37
fork() create a new process
Parent Child

• duplicated
• Address space
• Global local variables
• Current working directory
• Root directory
• Process resources
• Resource limits
• Etc

• Different
• PID
• Running time
• Running state
• Return values from fork()

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Return values of fork()

• Successful

child
0
fork()
parent
Childs PID

• Not Successful

child
fork()
parent
-1
errno is set to indicate error
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Return values of fork()

• The return value of the function is which
  discriminates the two processes of execution.
• Upon successful completion, fork() return 0 to
  the child process and return the process ID
  of the child process to the parent process.
• Otherwise, (pid_t)-1 is returned to the parent
  process, no child process is created, and errno
  is set to indicate the error.

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A simple C program on fork()

• include ltsys/types.hgt
• include ltstdio.hgt
• include ltunistd.hgt
• int value 5
• int main()
• pid_t pid
• pid fork()
• if (pid 0) / child process /
• value 15
• printf(CHILD value d\n, value) / Line A
  /
• else if (pid gt 0) / parent process /
• wait (NULL)
• value -10
• printf(PARENT value d\n, value) / Line
  B /
• exit(0)

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A simple C program on fork()

• Code can be downloaded from
• http//course.cs.ust.hk/comp252/web08fall/Lab1/tes
  tfork.c
• Compile
• gcc -o testfork testfork.c
• Run and understand the result
• ./testfork

42
A simple C program on fork()

• Line A CHILD value 20
• Line B PARENT value -5
• Upon fork() system call, the variable value is
  made a copy in the child process, so it prints
  out 51520
• after wait() system call, the child terminates
  and its copy of value is destroyed.
• The parent has value5, so it prints out 5-10
  -5.

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(Optional) Debugging

• Printf/Printk
• Simple programs can often be debugged efficiently
  with well placed print statements.
• See the example programs to see how we use print
  statements to verify the arguments supplied
• Kernel programming requires the use of printk for
  debugging.
• gdb
• The GNU debugger. An interactive debugger.
• Useful for debugging complex logic.
• gdb name_of_executable
• Starts GNU debugger (gdb) and loads the
  executable file into memory.

44
(Optional) GDB debugger

• Basic command is introduced here
• http//course.cse.ust.hk/comp252/web08fall/Others/
  GDB.htm
• http//www.dirac.org/linux/gdb/

45
(Optional) Gdb Practice

• Compilation
• cp /course/comp252/web08fall/Lab1/Makefile/gdb.c
  .
• gcc -g -o gdb_demo gdb.c
• gdb gdb_demo
• View the code
• list (view 10 lines of code)
• list (view next 10 lines of code)
• list - (view previous 10 lines of code)
• list 3,8 (view line 3 to line 8)
• Run it
• run 1 2 (run the program with arguments)

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(Optional) Gdb Practice

• Insert / delete breakpoint
• break 7 (inset a break point in line 7)
• info breakpoint (view break point information)
• delete 1 / clear 1 (delete break point 1)
• Enable / disable breakpoint
• break 7
• break 16
• run
• disable 3 (disable break point 3)
• run (can you see the different?)
• info breakpoint
• enable 3 (enable break point 3)

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(Optional) Gdb Practice

• Print out the value of a variable
• disable 3
• run (program will stop at line 7)
• print i (print out the current value of i)
• next (go to next line, it is line 6)
• step (go to next line, it is line 7)
• Note different between next and step
• print i (i become 1)
• continue (go to next break point, it is line 7
  again)
• Quit GDB
• quit