Introduction to the Omega Server CSE 1105

Overview Intro to Omega Basic Unix Command Files Directories Printing C and C++ compilers GNU Debugger

Omega Server Unix-based Server Provides C, C++, Lisp, Prolog, Cobol, and Fortran Language Compilers Pine Mail Server Users connect via telnet, ssh, hummingbird or other remote log ins

How to connect to Omega 1. Using the telnet command > telnet omega.uta.edu 2. Enter username at the prompt

Connect 2. SSH Secure Shell installed on all school computers

Connect 3. Hummingbird

Writing programs Edit a file using an existing Unix editor vi editor pico editor Edit a text file and upload it to omega telnet ftp content or attachment

Basic Unix Commands Managing Files ls : displays the files in a specified directory %ls rm : delete a file %rm file_name cp : copy files %cp source_file destination_file mv : renames files and/or moves files %mv old_filename new_filename %mv old_filename directory/new_name

pwd: print the current (working) directory %pwd cd: change directory %cd subdirectory_name %cd.. mkdir: make a new directory %mkdir subdirectory_name rmdir: remove a directory %rmdir subdirectory_name Basic Unix Commands Managing Directories

Basic Unix Commands Printing Files cat: concatenate the file to the screen (list the file) %cat file_name : or pipe the file to a selected output location %cat file_name | output_loc lpr: send to the printer %lpr file_name

Basic Unix Commands Invoking C and C++ compilers gcc: compile a C program to output file a.out %gcc program_file.c : with the math library option to a file my.out %gcc program_file.c -lm -o my.out g++: compile a C++ program to file a.out % g++ program_file.cpp

GNU Debugger (GDB) Use GDB to debug programs in C, C++, Modular-2, and Pascal, Fortran GDB is part of the GNU Project that was launched in 1984 to develop a complete UNIX style operating system.GNU Project Free software: the GNU system is free ( pronounced “guh-noo”) at software GDB is protected by the GNU General Public License (GPL)

Capabilities with GDB Start your program, specifying anything that might affect its behavior. Make your program stop on specified conditions. Examine what has happened, when your program has stopped. Change things in your program, so you can experiment with correcting the effects of one bug and go on to learn about another.

Starting GDB gcc filename with option –g gcc filename –g gdb in shell prompt with executable file gdb a.out gdb prompt – executing by gdb command (gdb) commands

GDB Commands list(l) – show the source list each 10line list [[file:]n|func] help – show the information of gdb command help [name] break – setup the breakpoint break [[file:]n|function]

GDB Commands - cont. clear – remove the breakpoint clear [[file:]n|function] run – begin program run [arglist] print expr – show the value of expr print expr

GDB Commands - cont. c (or continue) – continue the program c [n] next – execute n lines and display the line if the next line is the function, it executes the whole function. next [n]

GDB Commands - cont. step - execute n lines and display the line if the next line is the function, it executes n line inside the function. step [n] bt (or backtrace) – display the program stack’s order which functions are called in program

GDB Commands - cont. ret (or return) – exit the current function as return retrunvalue ret retval finish – execute the current function until the function returns the retval kill – quit the current debugging process quit – quit the gdb

Example – bugsome.c The program is to calculate factorial and power Not working for power function Setup the breakpoint as power function Program bugsome.c has been compiled with gcc to file a.out /home/dsk22/ xxx1234 /1320> gcc bugsome.c

#include /* returns n * (n-1) *... * 1 */ int factorial(int n) { if(n == 1) return 1; return n * factorial(n - 1); } /* returns b^e, e>=0 */ int power(int b, int e) { return b * power(b, e-1); } void f3() { printf("This is f3().\n"); } void f2() { f3(); printf("11^7 = %d\n", power(11, 7)); } void f1() { printf("11! = %d\n", factorial(11)); f2(); } int main() { f1(); printf("0! = %d\n", factorial(0)); return 0; } List – bugsome.c

Result – a.out /home/dsk22/ xxx1234 /1320> a.out 11! = This is f3(). Stack overflow: pid 315, proc a.out, addr 0x11fdfffe0, pc 0x bc /home: warning, disk quota exceeded for user id Segmentation fault (core dumped) /home/dsk22/xxx1234/1320>

Debugging example /home/dsk22/ xxx1234 /1320> gcc bugsome.c -g /home/dsk22/ xxx1234 /1320> gdb a.out GDB is free software and you are welcome to distribute copies of it under certain conditions; type "show copying" to see the conditions. There is absolutely no warranty for GDB; type "show warranty" for details. GDB 4.16 (alpha-dec-osf4.0), Copyright 1996 Free Software Foundation, Inc... (gdb) break power Breakpoint 1 at 0x d8: file bugsome.c, line 16.

Example continued (gdb) run Starting program: /home/dsk22/xxx1234/1320/a.out 11! = This is f3(). Breakpoint 1, power (b=11, e=7) at bugsome.c:16 16 return b * power(b, e-1); (gdb) c Continuing. Breakpoint 1, power (b=11, e=6) at bugsome.c:16 16 return b * power(b, e-1);

(gdb) c 3 Will ignore next 2 crossings of breakpoint 1. Continuing. Breakpoint 1, power (b=11, e=3) at bugsome.c:16 16 return b * power(b, e-1); (gdb) c Continuing. Breakpoint 1, power (b=11, e=2) at bugsome.c:16 16 return b * power(b, e-1); (gdb) c Continuing. Breakpoint 1, power (b=11, e=1) at bugsome.c:16 16 return b * power(b, e-1); (gdb) c Continuing. Breakpoint 1, power (b=11, e=0) at bugsome.c:16 16 return b * power(b, e-1);

(gdb) ret 1 Make power return now? (y or n) y #0 0x f8 in power (b=11, e=1) at bugsome.c:16 return b * power(b, e-1); (gdb) l 11 } /* returns b^e, e>=0 */ 14 int power(int b, int e) 15 { 16 return b * power(b, e-1); 17 } void f3() 20 {

(gdb) l 21 printf("This is f3().\n"); 22 } void f2() 25 { 26 f3(); 27 printf("11^7 = %d\n", power(11, 7)); 28 } void f1() (gdb) break 28 Breakpoint 2 at 0x c4: file bugsome.c, line 28. (gdb) c Continuing. 11^7 = Breakpoint 2, f2 () at bugsome.c:28 28 }

(gdb) n f1 () at bugsome.c:34 34 } (gdb) n main () at bugsome.c:41 41 printf("0! = %d\n", factorial(0)); (gdb) s factorial (n=0) at bugsome.c:7 7 if(n == 1) (gdb) l 2 #include 3 4 /* returns n * (n-1) *... * 1 */ 5 int factorial(int n) 6 { 7 if(n == 1) 8 return 1; 9 10 return n * factorial(n - 1); 11 }

(gdb) ret 1 Make factorial return now? (y or n) y #0 0x in main () at bugsome.c:41 41 printf("0! = %d\n", factorial(0)); (gdb) c Continuing. 0! = 1 Program exited normally. (gdb) quit