COM324 System Programming. Midterm Exam

Transcription

1 Name: COM324 System Programming Spring Computer Engineering Department Near East University Midterm Exam April 28, 2010 [11:30A] Lecturer: Hüseyin Sevay INSTRUCTIONS You have 100 minutes for this exam. This exam is worth a total of 104 points, and points above 100 are bonus. This question paper has 8 single-sided pages (except for this title page) and a total of 14 questions. Please check to make sure you have all the pages NOW! Please write your name and student ID in the boxes at the top of this page and your student ID on each remaining page NOW! Each question specifies how many points it is worth. Please write your answers in the allotted space/box(es) below or next to each question. Do not write your answers anywhere else! Especially please do not write below the footer line on question pages. Read each question carefully, and do not start answering a question before understanding what that question is asking for.

2 1. Suppose you have a C source file named prog.c. Provide a GNU/Linux command that would only compile this source code with all warning flags turned on. [3 points] 2. Provide a GNU/Linux command that would display on the screen the result of preprocessing C source file named main.c. [2 points] 3. Provide a GNU/Linux command for getting detailed help on the system call open. [2 points] 4. Provide a GNU/Linux command that lists all tasks started in the current terminal session. [2 points] 5. Provide the GNU/Linux command that periodically updates information on running processes on a given machine and can provide information such as which process is taking the most CPU and memory. [2 points] 6. Suppose you are running a process, and, say, with a process ID of What GNU/Linux command would you use in order to monitor this process? Provide the exact command. [2 points] 7. Describe briefly what the command chmod o+rw,g+r-w,o-rwx file.txt accomplishes. [5 points] PLEASE DO NOT WRITE IN THIS SPACE! Page 1 of 8

3 8. Consider the following commands in the given order. Suppose that a file named report.txt exists already. Assume that none of the files that are created by the commands below exist beforehand. Fill in the inode number and reference link count for each file entry printed by each ls command below. Note that some of the values have already been filled in for you on purpose. [14 points] % ls -ali report.txt inode number link count report.txt % ln report.txt h1.txt % ls -ali report.txt h1.txt inode number link count report.txt h1.txt % ln h1.txt h2.txt % ls -ali report.txt h1.txt h2.txt inode number link count report.txt h1.txt h2.txt % rm report.txt % ls -ali h1.txt h2.txt inode number link count h1.txt h2.txt PLEASE DO NOT WRITE IN THIS SPACE! Page 2 of 8

4 9. Write a C program (without #includes) that spawns a child process in which it executes the external command ls -a -lh. [10 points] PLEASE DO NOT WRITE IN THIS SPACE! Page 3 of 8

5 10. Consider the following C source code. Suppose that this code is compiled with the necessary #include files and linked in the current directory to produce an executable named mylseek. #define BUFSIZE 10 void reportcurrentoffset( int fd ) { off_t offset=lseek( fd, 0, SEEK_CUR ); } /* end reportcurrentoffset */ void initbuffer( char *buffer, char initchar, size_t bufsize ) { int i; for ( i=0; (i < bufsize); i++ ) { buffer[i] = initchar; } } /* end initbuffer */ int main( int argc, char **argv ) { int fd; char buffer[bufsize]; off_t offset; fd = open( argv[1], O_RDONLY ); if (fd < 0) { perror( "*** open" ); exit( 1 ); } read( fd, buffer, 2 ); read( fd, buffer, 3 ); offset = lseek( fd, 5, SEEK_CUR ); offset = lseek( fd, -2, SEEK_CUR ); read( fd, buffer, 4 ); offset = lseek( fd, 12, SEEK_SET ); read( fd, buffer, 2 ); offset = lseek( fd, -10, SEEK_END ); read( fd, buffer, 3 ); return 0; } /* end main */ PLEASE DO NOT WRITE IN THIS SPACE! Page 4 of 8

6 Suppose also that we have an input file named lseek.dat also residing in the current directory that contains only one line of data with the following contents: ABCDEFGH Suppose that we execute the program using the command./mylseek lseek.dat. What would this command print out to the screen? Solve this question carefully because each operation may affect the next! [15 points] PLEASE DO NOT WRITE IN THIS SPACE! Page 5 of 8

7 11. What will the following program output when executed (The order of output is critical.) Explain the output in sufficient detail. [15 points] #include <signal.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> void sigchld_handler( int signo ) { printf( "D\n" ); return; } /* end sigchld_handler */ int main( void ) { struct sigaction act; act.sa_handler = sigchld_handler; sigaction( SIGCHLD, &act, NULL ); if (fork() == 0) { sleep( 3 ); printf( "A\n" ); sleep( 2 ); exit( 0 ); } else if (fork() == 0) { sleep( 8 ); printf( "E\n" ); sleep( 5 ); exit( 0 ); } else { printf( "B\n" ); sleep( 50 ); printf( "C\n" ); sleep( 30 ); printf( "F\n" ); } /* end if */ return 0; } /* end main */ PLEASE DO NOT WRITE IN THIS SPACE! Page 6 of 8

8 12. Consider the following series of system calls. Explain in detail what effect is obtained after each sigprocmask call. [15 points] sigset_t seta, setb; sigfillset( &seta ); sigfillset( &setb ); sigdelset( &setb, SIGINT ); sigdelset( &setb, SIGTERM ); sigprocmask( SIG_SETMASK, &seta, NULL ); sigprocmask( SIG_UNBLOCK, &setb, NULL ); sigprocmask( SIG_UNBLOCK, &seta, NULL ); PLEASE DO NOT WRITE IN THIS SPACE! Page 7 of 8

9 13. Name the input and output devices associated with each stage of the compound GNU/Linux command sort file.dat grep -i "security" wc -l > sec.out before and after redirection. [12 points] 14. Blocked signals do not get lost. Is this statement true or false?. Explain briefly. [5 points] PLEASE DO NOT WRITE IN THIS SPACE! Page 8 of 8