CS 590Programming Environments with

UNIX

Computer Lab Accountwww.cs.uah.edu/account

Course Homepagewww.cs.uah.edu/~kkeen/CS590

LASER Lab N328

Some Background

UNIX UNIX System V BSDPOSIX

LINUX

LASER LAB

System Names:

catalina conquest crusader

dakota duchess havoc

hawker invader lightning

marauder

shrike whirlwind

Remote Access

PuTTY is a free telnet/SSH clientYou can download PuTTY here

Upload/Download requires SFTPYou can use PSFTP to upload/download.

Remote Access from UNIX/LINUX

ssh username@host

Ex: ssh kkeen@havoc.cs.uah.edu

What you are expected to already know

bash and simple shell operations Files and directories

File structure / . .. Absolute vs. relative paths File and directory permissions

File and directory commands cp, mv, scp (secure copy), rm, mkdir, rmdir, tar

Set up environment variables PATH, LD_LIBRARY_PATH

At least one text editor vi, emacs, pico

Strong C programming skills

Getting Help The man pages

section 1: User commandssection 2: system callssection 3: library callssection 4: special or device filessection 5: file formats and conventionssection 6: games for linuxsection 7: macro packages and conventionssection 8: system management commands

UNIX/LINUX System Overview

Apps

Shell

Kernel

H.W.

System call

interface

Multi UserMulti Process system

Every user has a UID Every user belongs to at least one

UNIX group GID Root always has UID of 0

Programs and Processes

A program is an executable file A process is an executing instance

of a program

Kernel Mode vs. User Mode

User mode Most apps run in this mode

Kernel mode “trusted” code

System Calls

AppC Library

func

func

func

func

func

func

Kernel

System Call Error Handling

For most system calls, return values are: 0 – success Negative number – failure

errno perror strerror

perror

void perror (const char *msg);

Prints the text in msg followed by a colon and text description of the error number.

perror example

FILE *myFile;myFile = fopen(“file.txt”, “r”);if(myFile == NULL) { perror(“unable to open file”);}

strerror

char *strerror(int errnum);

Prints out text for given error number. Can be used as part of a larger error message.

strerror example

FILE *myFile;myFile = fopen(“file.txt”, “r”);if(myFile == NULL) { fprintf(stderr, “unable to open file:

%s”, strerror(errno));}

Basic IPC - Signals

Inter Process Communication (IPC). Most basic form is via signals. Used to notify a process of some condition.

We can catch signals and Ignore them Let default action take place Call a custom signal handler

Example Program

Files and Directories http://www.cs.uah.edu/~kkeen/CS590/examples/intro/pseudols

More about files and directories in chapter 4

Time in UNIX

Historically Calendar Time Process Time

Clock Time User CPU Time System CPU Time

Command Line Arguments

int main(int argc, char** argv)int main(int argc, char *argv[]) argc – argument count argv – array of character pointers Dealing with numbers

atoi atof

getoptint getopt(int argc, char* const argv[], const char *optstring);

Function to allow easy parsing of command line options

Looks for options we specify Sets optarg and optind Can specify required argument by

using ‘:’ after the option in optstring

getopt_long

Uses two dashes instead of one Allows longer, more descriptive

options.