cs 590 programming environments with unix. computer lab account course homepage kkeen/cs590
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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.
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.