1. CMPT 471 Networking II Linux Primer 1© Janice Regan, 2013

2. Shell Scripts  A shell script is an executable file containing a series of shell commands. When the shell script is executed the commands in the file are executed in sequence by the shell.  A shell script records a series of command line actions and easily executes them again and again  Assures repeatability of experiments and processes  Allows long series of commands to be easily tested and debugged  There are different shell scripting languages such as  csh (C shell), tcsh  sh (Bourne shell), bash (Bourne again shell)  Perl …… © Janice Regan, 2013 2

3. Selecting a Shell Script Language  On the command line type  the name of the shell followed by return to enter the shell.  exit followed by return to leave the shell.  To determine which default shell you are presently using echo $SHELL finger youruserid (your default shell)  The present shell will be indicated by the prompt  To indicate which shell to use inside a shell script  in the first line of your script file#! /bin/csh  To indicate which shell to use when executing a shell script called scriptname  bash scriptname arguments or csh scriptname arguments © Janice Regan, 2013 3

4. Executing a Shell Script  Your script file must be executable, you will need to change the permissions to make it executable (discuss how later in this lecture)  Executing a shell script called scriptname  bash scriptname arguments  csh scriptname arguments  source scriptname arguments ./scriptname arguments © Janice Regan, 2013 4

5. Using Basic Unix Commands  Any basic Unix command can be run from the command line, or from within a shell script  To work with shell scripts you must first be familiar with basic Unix commands  Commands are used to move around within the file system, to create and operate on files, to interact with the operating system © Janice Regan, 2013 5

6. Some basic commands  Remember UNIX is case sensitive  yppasswd username (username is optional)  Executed from your command line  Will ask you to input your old password and your new passwd twice  You can only change your own passwd unless you are root  man commandname or info commandname  Tell me how to use the command with name commandname  su  Become the root user (superuser, substitute user)  You will need to be root to complete many of your assignments. Do so with care..  whoami Tell me my username © Janice Regan, 2013 6

7. Directories  Directory creation, navigation, removal  mkdir directorynamemake directory directoryname  rmdir directorynameremove empty directory  cd directorypathgo to directory directorypath  ls directorypathlist files in directory directorypath  cdreturn to your home directory  lslist files in this directory  pwdshow path to and name of current directory  cd..Move to the parent directory of this directory (one layer further up the directory tree © Janice Regan, 2013 7

8. Directory structure Dir1 Dir5Dir6Dir7 © Janice Regan, 2013 8  In myhome  cd Dir2 (goes to Dir2 )  cd Dir2/Dir5 (goes to Dir5 )  In Dir5  cd.. (goes to Dir3)  cd../.. Or cd (goes to myhome)  cd../Dir6 (goes to Dir6)  Anywhere cd will take you to myhome (your home directory)  cd / takes you to the root directory myhome Dir2Dir3Dir4

9. Root file structure © Janice Regan, 2013 9

10. Files  To make a file open it using your favorite text editor  mv filepath1 filepath2  Moves (renames) a file or directory  mv a b file previously named a is now named b  mv a../a file a is moved from the present directory to the parent directory of the present directory  rm filepathremoves (deletes) a file  rm a deletes file a from the current directory  rm../a removes file a from the parent of the present directory  grep pattern filepaths  Find all occurrences of pattern in requested files © Janice Regan, 2013 10

11. Files  more filename or less filename  Displays contents of file filename one page (screen) at a time  cp filename1 filename2  Make a copy of filename1 with name filename2  cat filename1 filename2 filename3  Will print the contents of each file in sequence Contents of filename1 Contents of filename2 Contents of filename3 © Janice Regan, 2013 11

12. Wildcards  Wildcards are used to represent multiple possibilities  * matches any number of characters  ? Matches a single character  Examples  ls a? List all files in the current directory beginning with a and having a name of length 2 characters.  grep mystring */*file Find all occurences of the string “mystring” in all files whose names end with the string “file”. The files ending with string “file” must be in a subdirectory of the present directory  rm [a-c]* Remove all files with filenames beginning with a b or c from the current directory © Janice Regan, 2013 12

13. Redirection  Redirect input and/or output  > filename redirect standard output from screen to file. cat file1 file2 file3 > f4 A new file f4 is opened and the contents of file1, file2 and file 3 are successively added to the file f4. If f4 exists it will be overwritten.  < filename take input from file filename a.out < datafile (a.out is the default output file for a compiled executable)  >> filename redirect standard output from screen to file. Appends output to an existing file cat file1 file2 file3 >> f4 The contents of file1 then file2 then file3 will be successively appended to the current contents of f4 © Janice Regan, 2013 13

14. Piping  Piping allows you to send the output of one process to become the input of another process without using io to store it in an intermediate file  ls a* | more List the files in the current directory whose names start with a, one page at a time © Janice Regan, 2013 14

15. File Permissions  Can use ls –l to find present permission for files  drwxrwxrwxfor directory  -rwxrwxrwxfor file u g o  3 sets of permissions  User (u) group (g) other(o)  Each set allows or disallows read write & or execute  rwx (allow all)  rw- (read write allowed)  r - - (read only)  Order of sets is ugo © Janice Regan, 2013 15

16. Setting File Permissions: 1  Permissions can be reset by using chmod  chmod can specify permission in two ways  Numeric values read(4) write(2) execute(1). Sum desired values to give one digit permission value for each set Read write and execute 7, Write 2, Read and Execute 5  Adding or removing particular permissions Add execution permissions for user chmod u+x filename Remove write permissions for other chmod o+w filename Add read permissions for everyone chmod a+r filename © Janice Regan, 2013 16

17. File Permissions Examples  chmod u-x filename  (remove owners execute permission)  chmod a+w filename  (make the file readable for all users)  chmod 644 filename  (make the file readable for all users but writeable only by the owner)  chown newowner filename  (you must own the file or be root)  chgroup newgroup filename © Janice Regan, 2013 17

18. Processes  Command &  Run command as a background process  cntrlZ  Suspend (temporarily stop) foreground process  bg Move suspended process to background  fg Move background process or suspended process to the foreground  cntrlC  Terminate the foreground process © Janice Regan, 2013 18

19. Processes  ps or ps -l  List information about all current processes  kill pidnumber  Kill background process with PID pidnumber  (use ps to find the pidnumber of the process) ps -l F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD 8 S 37636 7058 7054 0 46 20 ? 273 ? pts/38 0:01 csh 8 S 37636 7072 7058 0 51 20 ? 296 ? pts/38 0:00 bash  To assure a process will die use kill -9 pidnumber © Janice Regan, 2013 19

20. Checking shared memory  check after your process terminates jregan@cs-nx-01:~$ ipcs ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x00000000 1885601818 jregan 600 393216 2 dest ------ Semaphore Arrays -------- key semid owner perms nsems 0x00000000 5373963 dwlouie 666 25 ------ Message Queues -------- key msqid owner perms used-bytes messages © Janice Regan, 2013 20

21. When shared memory is left  When you still have entries in the shared memory section  Look at the value in the nattach (number of attached processes) if it is 0 then you can remove the memory segments using the provided script cleanSem © Janice Regan, 2013 21

22. Using the cleanSem script  Copy the script from the class website  Change the mode of the file you now have in your LINUX directory so it can be executed  Chmod +x cleanSem  Run the script twice. To run ./cleanSem © Janice Regan, 2013 22

23. When shared memory is left  When you still have entries in the shared memory section  Look at the value in the nattach (number of attached processes) if it is not 0 then the memory segments are still connected to at least one process  You need to find and remove that process © Janice Regan, 2013 23

24. Removing processes (300)  Find the processes that are connected to your shared memory  If your userid is myuserid ps ux | grep myuserid | grep fork  Look at the resulting list of processes, finding one that did not start at the time you logged in. Kill that process (kill -9 processid) © Janice Regan, 2013 24

25. Removing other processes  Find the processes that are part of your last run.  If your userid is myuserid and you ran executable./myprog ps ux | grep myprog  Kill the processes that include./myprog © Janice Regan, 2013 25