% CST8207 Assignment 13 - GRUB, Run Levels, services, telinit, chkconfig % Ian! D. Allen - idallen@idallen.ca - www.idallen.com % Winter 2013 - January to April 2013 - Updated Wed May 8 21:04:29 EDT 2013 Due Date and Deliverables ========================= - **Due Date**: `13h30 (1:30pm) Wednesday April 24, 2013 (start of exam)` - NOTE: This is the LAST assignment. The department recommends that you finish all your assignments *before* exams begin. - Late assignments or wrong file names may not be marked. Be accurate. - **Available online**: - Version 1: 12:55 Sunday April 7, 2013 (checking program not ready yet) - **Prerequisites**: - The current [Class Notes]. - Linux Fedora 12 installed in a virtual machine via [Fedora 12 Virtual Machine] - From previous assignments, you need working modifications to the [GRUB Configuration File] and modifications to enable [`sudo`]. - An ability to **READ ALL THE WORDS** to work effectively. - **Deliverables**: 1. Modifications to your [Fedora 12 Virtual Machine] as given in this assignment. - **Do not delete any assignment work from your [Fedora 12 Virtual Machine] until after the term is over!** 2. Directory structure and files created and left for marking on the [Course Linux Server] (**CLS**). - **Do not delete any assignment work from the CLS until after the term is over!** 3. One text file uploaded to Blackboard according to the steps in the [Checking Program] section below. **WARNING:** Some inattentive students upload Assignment #13 into the Assignment #12 upload area. Don’t make that mistake! Be exact. Purpose of this Assignment ========================== This assignment is based on your weekly [Class Notes]. All work is done in your own [Fedora 12 Virtual Machine]. 1. Configure [Booting and GRUB]. 2. Practice listing and modifying services in various Run Levels. 3. Practice starting and stopping system services. Remember to **READ ALL THE WORDS** to work effectively and not waste time. Introduction and Overview ========================= This is an overview of how you are expected to complete this assignment. Read all the words before you start working. 1. Complete the [Tasks] listed below. 2. Verify your own work before running the [Checking Program]. 3. Run the [Checking Program] to help you find errors. 4. Submit the output of the [Checking Program] to Blackboard before the due date. 5. **READ ALL THE WORDS** to work effectively and not waste time. > Since I also do manual marking of student assignments, your final mark may > not be the same as the mark submitted using the current version of the > [Checking Program]. I do not guarantee that any version of the [Checking > Program] will find all the errors in your work. Complete your assignments > according to the specifications, not according to the incomplete set of the > mistakes detected by the [Checking Program]. When you are finished the tasks, leave the files and directories in place as part of your deliverables. **Do not delete any assignment work until after the term is over!** Assignments may be re-marked at any time; you must have your term work available right until term end. Searching the course notes -------------------------- All the course notes are always available on the Internet here: [CST8207 GNU/Linux Operating Systems I]. All the current and previous terms notes files are also stored on the CLS. You can learn about how to read and search these notes files using the command line on the CLS under the heading *Copies of the CST8207 course notes* near the bottom of the page [Course Linux Server]. The Source Directory -------------------- All references to the “Source Directory” below are to the CLS directory `~idallen/cst8207/13w/assignment13/` and that name starts with a *tilde* character “`~`” followed by a userid with no intervening slash. The leading tilde indicates to the shell that the pathname starts with the HOME directory of the account `idallen`. Tasks ===== - Do the following tasks in order, from top to bottom. - Pay attention as to which tasks must be done in your own [Fedora 12 Virtual Machine] and which must be done in your account on the [Course Linux Server]. - **READ ALL THE WORDS!** and do not skip steps. Set Up ------ 1. On the [Course Linux Server], make the directory `CST8207-13W/Assignments/assignment13`, in which some information will be stored related to this assignment. 2. Create the `check` symbolic link needed to run the [Checking Program], as described in the section [Checking Program] below. 3. Complete your [Fedora 12 Virtual Machine] Installation. 4. From previous assignments, finish the modifications to the [GRUB Configuration File] and modifications to enable [`sudo`]. 5. On your [Fedora 12 Virtual Machine] also create a directory in your own account named `CST8207-13W/Assignments/assignment13` (exactly the same directory hierarchy as you created on the CLS). 6. Before you begin this assignment, create a snapshot of your [Fedora 12 Virtual Machine]. - Enter a comment explaining where and when you took this snapshot. - You can restore back to this snapshot if anything goes wrong. Worksheet 13 - Booting and GRUB ------------------------------- 1. Before you start the following worksheet, save a copy of your current 17-line GRUB configuration file into file `grub-before` in your Fedora 12 `assignment13` directory. You will need this saved file later. 2. Review the course notes on [Booting and GRUB]. 3. Complete [Worksheet #13 ODT] in your [Fedora 12 Virtual Machine]. 4. Save your post-worksheet GRUB configuration file (the one you created by doing the [Worksheet #13 ODT] above) into file `grub-after` in your Fedora 12 `assignment13` directory. Configure a GRUB boot menu -------------------------- - Work in this section is based on work done in [Worksheet #13 PDF]. - Review the course notes on [Booting and GRUB]. 1. Take a VM snapshot if you haven’t done so already. 2. Restore your GRUB configuration file to its saved 17-line pre-worksheet version (`grub-before`) that you started with before you added the passwords and new **boot menu entries** in [Worksheet #13 PDF]. - Your pre-worksheet GRUB configuration file was only 17 lines long. - It had only one four-line Fedora boot menu entry and no password lines. - The `timeout` was set to 30 seconds set in a [previous assignment][GRUB Configuration File]. - *(If you forgot to save your pre-worksheet configuration file, you can start up an early snapshot of your VM, made before you did the worksheet, and use [File Transfer] to copy the pre-worksheet configuration file to the CLS, and then copy it back to Fedora.)* 3. Edit your restored 17-line GRUB configuration file as follows: copy the existing default four-line **boot menu entry** and create three new ones below it, for a total of four boot menu entries. Each new boot menu entry is a copy of the original four-line boot menu entry. Adding three more boot menu entries means adding a total of 12 additional lines. The resulting file will be 17+12=29 lines long. Do not make any changes to the first four-line **boot menu entry**. You have created three new four-line **boot menu entries**. In each of the three new boot menu entries, insert the words given below at the start of the `title` for that boot menu entry, as you did for the boot menu entries you added in [Worksheet #13 PDF]. Make the following changes to each of the three *new* boot menu entries: 4. For the second boot menu entry (the first *new* one): a) Change the `title` to start with: `single user` in front of `Fedora`. b) Remove the Red Hat Graphical Boot and `quiet` options. c) Configure this entry with a kernel option to boot in single-user mode. 5. For the third boot menu entry (the second *new* one): a) Change the `title` to start with: `text only` in front of `Fedora`. b) Remove the Red Hat Graphical Boot and `quiet` options. c) Configure this entry with a kernel option to boot in full multi-user but text-only mode (no GUI). 6. For the fourth boot menu entry (the third *new* one): a) Change the `title` to start with: `default` in front of `Fedora`. b) Remove the Red Hat Graphical Boot and `quiet` options. 7. Make the following changes to the top section of your GRUB configuration file, before all the boot menu sections: a) Have GRUB time out after `45` seconds. b) Have GRUB ask for an encrypted password: `grublock` c) Have GRUB choose the fourth (last) `default` boot menu entry when the system reboots. d) Comment-out the `splashimage` line. (Make it a comment in the same way as you made `hiddenmenu` into a comment in a [previous lab][GRUB Configuration File].) 8. Save your changes. Reboot. You should find that GRUB has no blue background image and that it automatically chooses the fourth boot menu entry, the one with the words `default Fedora` at the start of the title, after 45 seconds of count-down. 9. Log in and check your work using the [Checking Program]. Changing System V Run Levels ---------------------------- See the section on Legacy Run Levels and Services in the [Booting and GRUB][1] page. You will need to use the `sudo` command to run the privileged commands in this section. 1. Login in to the Fedora 12 GUI as your ordinary (non-`root`) account and start a terminal. 2. Copy the seven-line description of Run Levels from the comments in your Fedora 12 `inittab` file to a new file `runlevelhelp` in your Fedora 12 `assignment13` directory. Your new file should have a `wc` of `7 56 252`. (Hint: You can use `grep` with a pattern that matches in just these seven lines, or you can copy the whole file and text-edit away the other lines.) 3. Copy the default run level line from your Fedora 12 `inittab` file to file `initdefault` in your Fedora 12 `assignment13` directory. Your new file should have a `wc` of `1 1 18`. 4. Use the command that displays your previous and current Run Level and save the output into file `runlevel5-before` in your Fedora 12 `assignment13` directory. Your new file should have a `wc` of `1 2 4`. Look at the contents of the file to see the previous and current run level numbers. (You should be in Run Level 5 now.) 5. Count all the processes running on your machine. (The count should be about 150 processes in Run Level 5.) - **NEW 5B:** Some people (me included) are finding that switching to Run Level three leaves them with nothing but a black screen on the VMware console. This appears to be a VMware problem, since it only happens with newer versions of VMware. If this happens to you, here are some ways to work around it: i. Use a terminal program to connect to your VM, as follows: a) You will need an SSH terminal program outside your Fedora 12 VM, e.g. Windows PuTTY or Linux `ssh` running on your host computer (not on your Fedora VM). b) Before you change Run Levels, use `ifconfig eth0` on your Fedora VM to find the IP address of your Fedora VM. (Running the `ifconfig` program may need a ROOT search PATH.) c) Use the terminal program on your host computer to connect to and log in to your Fedora 12 VM using the IP address and SSH protocol (similar to how you connect to the CLS). d) Use this SSH terminal connection to change run levels. As long as you don’t go down to single-user mode (where terminal connections aren’t allowed), you can change Run Levels using the terminal, and you won’t be affected by the “black screen” problem. ii. If the above doesn’t seem like a good work-around, try this. (This may or may not work. The above terminal work-around always works.) Before going to Run Level 3, switch to the Fedora text console and back, as follows: a) Read this entire section through before you do it, since you are about to switch away from your GUI screen and you need to know how to get back again. b) Click to give mouse focus to your Fedora VM console graphical screen. c) Push and hold down both the `CTRL` and `ALT` shift keys, then push the Function Key `F1` with both `CTRL` and `ALT` held down. (This is similar to typing `CTRL+ALT+DELETE` but you are typing `CTRL+ALT+F1` instead.) d) You should switch to a black screen with some system messages on it. If not, try `CTRL+ALT+F1` again. If it still doesn’t work, change your VMware Hot Keys to be something other than `CTRL+ALT` using the **Edit|Preferences** menu and try again. If that still doesn’t work, give up and use the previous work-around (use a terminal program) instead. e) In the black console screen, push the `Enter` key once or twice and you should see a Fedora login banner with a `login:` prompt and cursor. You do not need to log in yet. f) Push and hold down just the `ALT` shift key, then push the Function Key `F7` with just `ALT` held down: `ALT-F7` g) Your Fedora GUI screen should return. h) You can use `CTRL+ALT+F1` and `ALT-F7` to switch back and forth. i) Return to the GUI screen. 6. Using the terminal and command line, change your run level to run level 3. - Hint: You will need to use a prefix command to run the command to change run levels with `root` privileges. - This run level change will kill your terminal, web browser, and anything else you have open in the graphical GUI! - The X11 GUI will disappear from the VMware console and you should see a black Fedora console login screen with messages. - In the black console screen, push the `Enter` key once or twice and you should see a Fedora login banner with a `login:` prompt and cursor. - If you see nothing but a black screen on your VMware console, with no text, use the previous work-arounds in the previous step, above. 7. Log in to the black console screen as your regular account. - If you see nothing but a black screen on your VMware console, use the work-arounds given in the previous step, above. 8. Use the command that displays your previous and current Run Level and save the output into file `runlevel3` in your Fedora 12 `assignment13` directory. Your new file should have a `wc` of `1 2 4`. Look at the contents of the file to see the previous and current run level numbers. (You should be in Run Level 3 now.) 9. Place a full list of all processes for all users, **BSD** format, all users, text user name (not numeric UID), full wide listing (not truncated at all), into file `psbsd3` in your Fedora 12 `assignment13` directory. It should be “approximately” 100 lines and 8KB while in Run Level 3. One of the very long lines will look similar to this (use `grep` to find it in the output): root 1495 0.0 0.1 2676 880 ? S Mar27 0:00 /sbin/dhclient -d -sf /usr/libexec/nm-dhcp-client.action -pf /var/run/dhclient-eth0.pid -lf /var/lib/dhclient/dhclient-ad12d8a2-c7c0-4c10-9847-6a0c3bc3818f-eth0.lease -cf /var/run/nm-dhclient-eth0.conf eth0 10. Change your run level from Run Level 3 to Run Level 2. In the VMware console screen, you will see status messages as the system stops and starts processes to correspond to the new Run Level. (You won’t see these if you are using a terminal connection.) 11. If necessary, log in again to the black console screen as your regular sysadmin account. 12. Use the command that displays your previous and current Run Level and save the output into file `runlevel2` in your Fedora 12 `assignment13` directory. Your new file should have a `wc` of `1 2 4`. Look at the contents of the file to see the previous and current run level numbers. (You should be in Run Level 2 now.) 13. Place a full list of all processes for all users, **UNIX** format, all users, text user name (not numeric UID), full wide listing (not truncated at all), into file `psunix2` in your Fedora 12 `assignment13` directory. It should be “approximately” 88 lines and 6KB while in Run Level 2. One of the very long lines will look similar to this (use `grep` to find it in the output): root 1495 1483 0 Mar27 ? 00:00:00 /sbin/dhclient -d -sf /usr/libexec/nm-dhcp-client.action -pf /var/run/dhclient-eth0.pid -lf /var/lib/dhclient/dhclient-ad12d8a2-c7c0-4c10-9847-6a0c3bc3818f-eth0.lease -cf /var/run/nm-dhclient-eth0.conf eth0 14. Change your run level from Run Level 2 back to Run Level 5. In the VMware console screen, you will see status messages as the system starts processes to correspond to the new Run Level and then the X11 GUI will start up again and give you a full graphical login screen. (You won’t see these if you are using a terminal connection.) 15. Use the command that displays your previous and current Run Level and save the output into file `runlevel5-after` in your Fedora 12 `assignment13` directory. Your new file should have a `wc` of `1 2 4`. Look at the contents of the file to see the previous and current run level numbers. (You should be in Run Level 5 again.) 16. Count all the processes running on your machine. The count should again be about 150 processes in Run Level 5. 17. Check your work using the [Checking Program]. Changing Run Level Services --------------------------- See the section on Legacy Run Levels and Services in the [Booting and GRUB][1] page. You will need to use the `sudo` command to run the privileged commands in this section. 1. Login in to Fedora 12 as your ordinary (non-`root`) account. 2. Save a listing of all services and all run levels into file `chkconfig-before` in your Fedora 12 `assignment13` directory. It should be “approximately” 57 lines and 3KB. One of the lines should look like this: httpd 0:off 1:off 2:off 3:off 4:off 5:off 6:off 3. Disable (turn off) the **Bluetooth** service in all run levels. 4. Completely remove the `smolt` service from `chkconfig` management. 5. Enable the **Apache HTTP Server** service only in Run Level 5. 6. Save a second listing of all services and all run levels into file `chkconfig-after` in your Fedora 12 `assignment13` directory. It should be “approximately” 56 lines (one line less than the *before* version) and 3KB. One of the lines should now look like this: httpd 0:off 1:off 2:off 3:off 4:off 5:on 6:off 7. Use the `diff` command to compare the *before* listing file with the *after* listing file. Two lines have changed and one line was deleted. 8. Check your work using the [Checking Program]. Manually Starting/Stopping Services ----------------------------------- See the section on Legacy Run Levels and Services in the [Booting and GRUB][1] page. You will need to use the `sudo` command to run the privileged commands in this section. 1. Start the Apache HTTP Server service using the `service` command. 2. Confirm that the Apache service is running by using the Firefox web browser inside Fedora 12 to open the web URL `http://localhost/`. You should see the `Fedora Test Page`. Close the web browser. 3. Use the `lpc stat` command to display the printers known to your Fedora 12 system. (You should see your `lp126` printer in the list.) 4. Stop the CUPS printer service using the `service` command. - What does the acronym CUPS stand for? 5. Try `lpc stat` again and see *no output* at all – CUPS is not running. 6. Try the `lpq` command and note the `unable to connect` error message. 7. Redirect the above `lpq` error message into file `lpq-stderr` in your Fedora 12 `assignment13` directory. (You may need to remember how to [redirect standard error] to a file.) 8. Start the CUPS printer service again. 9. Check your work using the [Checking Program]. When you are done ----------------- When you are finished, run the [Checking Program] to create an overall mark. Submit the output to Blackboard in the correct location. > Since I also do manual marking of student assignments, your final mark may > not be the same as the mark submitted using the current version of the > [Checking Program]. I do not guarantee that any version of the [Checking > Program] will find all the errors in your work. Complete your assignments > according to the specifications, not according to the incomplete set of the > mistakes detected by the [Checking Program]. 1. Optional: Keeping your base [Fedora 12 Virtual Machine] snapshot, remove any intermediate snapshots you no longer require, to free up disk space. - Be careful not to remove your current work! Checking, Marking, and Submitting your Work =========================================== The checking program resides on the [Course Linux Server], but your work is on your [Fedora 12 Virtual Machine]. There is a new **Fetch** program that you must download and use on your Fedora 12 machine to copy information from your Fedora 12 Virtual Machine to your account on the CLS so that the checking program can check it on the CLS. Once the **Fetch** program has fetched these files from your Virtual Machine to the CLS, you can run the checking program on the CLS to check what is saved in the files. When you make changes on your Fedora 12 Virtual Machine, you need to run the **Fetch** program again to update the saved files on the CLS. Simply running the checking program on the CLS will *not* update the saved files on the CLS. You must run the **Fetch** program when you make changes on your Fedora 12 Virtual Machine. Part I - Fetch and Check ------------------------ Do all the following steps on your [Fedora 12 Virtual Machine]. Read through the whole list before you start typing anything. 1. Log in to Fedora 12 as your non-`root` account (same userid as Blackboard). 2. Create a directory in your account named `CST8207-13W/Assignments/assignment13` (exactly the same directory hierarchy as you already have on the CLS). 3. Change to your above `assignment13` directory. 4. As shown below, use `wget` to get a copy of the **Fetch** program from this URL into a file named `do.sh`: Fedora$ wget -O do.sh http://teaching.idallen.com/cst8207/13w/notes/data/assignment13wget.sh `do.sh' saved [545/545] # size may differ slightly Make sure you have a file named `do.sh` in your directory. You only need to download this once per assignment. 5. As shown below, use `sudo` and `sh` to run the `do.sh` script you just downloaded to Fedora 12 with the `USER` environment variable set to your own CLS account userid (as stored in the `USER` variable). Fedora$ sudo USER=$USER sh do.sh 6. This **Fetch** program will connect from Fedora 12 to the CLS using your account name. It will copy files from Fedora 12 to your `assignment13` directory on the CLS. It will then run the checking program on the CLS to check your work. You will need to answer one question about your IP address, and then wait and type in your CLS password. It will look something like this: Fedora$ whoami abcd0001 Fedora$ hostname abcd0001 Fedora$ pwd /home/abcd0001/CST8207-13W/Assignments/assignment13 Fedora$ wget -O do.sh http://teaching.idallen.com/cst8207/13w/notes/data/assignment13wget.sh `do.sh' saved [545/545] # size may differ slightly Fedora$ sudo USER=$USER sh do.sh --------------------------------------------------------------------------- abcd0001: FETCH version 1. Connecting to CLS as USER='abcd0001' using ssh --------------------------------------------------------------------------- abcd0001: Use local Algonquin IP cst8207-alg.idallen.ca [y/N]? n abcd0001: Please wait; using ssh to connect to user 'abcd0001' on cst8207.idallen.ca ... *** COURSE LINUX SERVER *** abcd0001@cst8207.idallen.ca's password: # enter your CLS password --------------------------------------------------------------------------- idallen-ubuntu assignment13fetch_server.sh version 0 run by abcd0001. Please wait; collecting info from abcd0001 Virtual Machine --------------------------------------------------------------------------- VM files collected into CST8207-13W/Assignments/assignment13/abcd0001.tar.bz on CLS. Now running check program for abcd0001 on CLS: ---------------------------------------------------------------------------- idallen-ubuntu check: CST8207-13W/Assignments/assignment13 check program version 00 *** Checking account for abcd0001 on idallen-ubuntu *** [... checking program output appears here ...] ### Notes on the Fetch program - This **Fetch** program updates your saved files on the CLS and then runs the checking program on the CLS. If you only run the checking program on the CLS, it won’t update the files from your Fedora 12 VM and will check the exiting files saved under `assignment13` on the CLS. - The checking program is running on the CLS, not on your Fedora 12 VM. At the start, the checking program will issue messages relevant to your account on the CLS (e.g. errors in your CLS `.bashrc` file or world-writable files on the CLS). These errors are on the CLS, not on your Fedora 12 machine. Part II - Check and Submit -------------------------- When you are done with your assignment, you need to run the checking program one last time on the CLS and submit the output file, as follows: Do all this on the [Course Linux Server]: 1. There is a [Checking Program] named `assignment13check` in the [Source Directory] on the CLS. Create a [Symbolic Link] to this program named `check` under your new `assignment13` directory so that you can easily run the program to check your work and assign your work a mark. Note: You can create a symbolic link to this executable program but you do not have permission to read or copy the program file. 2. Execute the above “check” program on the CLS using its symbolic link. (Review the [Search Path] notes if you forget how to run a program by pathname from the command line.) This program will check your work, assign you a mark, and display the output on your screen. (You may want to paginate the long output so you can read all of it.) You may run the “check” program as many times as you wish, to correct mistakes and get the best mark. Some tasks sections require you to finish the whole section before running the checking program at the end; you may not always be able to run the checking program successfully after every single task step. 3. When you are done with checking this assignment, and you like what you see on your screen, redirect the output of the [Checking Program] into the text file `assignment13.txt` under your `assignment13` directory on the CLS. Use the *exact* name `assignment13.txt` in your `assignment13` directory. You only get *one* chance to get the name correct. Case (upper/lower case letters) matters. Be absolutely accurate, as if your marks depended on it. Do not edit the file. 4. Transfer the above `assignment13.txt` file from the CLS to your local computer and verify its contents. Do not edit this file! No empty files, please! Edited or damaged files will not be marked. You may want to refer to your [File Transfer] notes. 5. Submit the `assignment13.txt` file under the correct Assignment area on Blackboard (with the exact name) before the due date. Upload the file via the **assignment13** “Upload Assignment” facility in Blackboard: click on the underlined **assignment13** link in Blackboard. Use “**Attach File**” and “**Submit**” to upload your plain text file. No word-processor documents. Do not send email. Use only “Attach File”. Do not enter any text into the **Submission** or **Comments** boxes on Blackboard; I do not read them. Use only the “**Attach File**” section followed by the **Submit** button. (If you want to send me comments about your assignment, use email.) 6. Your instructor may also mark the `assignment13` directory in your CLS account after the due date. Leave everything there on the CLS. **Do not delete any assignment work from the CLS until after the term is over!** Use the *exact* file name given above. Upload only one single file of plain text, not HTML, not MSWord. No fonts, no word-processing. Plain text only. Did I mention that the format is plain text (suitable for VIM/Nano/Pico/Gedit or Notepad)? **NO EMAIL, WORD PROCESSOR, PDF, RTF, or HTML DOCUMENTS ACCEPTED.** No marks are awarded for submitting under the wrong assignment number or for using the wrong file name. Use the exact name given above. WARNING: Some inattentive students don’t read all these words. Don’t make that mistake! Be exact. **READ ALL THE WORDS. OH PLEASE, PLEASE, PLEASE READ ALL THE WORDS!** -- | Ian! D. Allen - idallen@idallen.ca - Ottawa, Ontario, Canada | Home Page: http://idallen.com/ Contact Improv: http://contactimprov.ca/ | College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/ | Defend digital freedom: http://eff.org/ and have fun: http://fools.ca/ [Plain Text] - plain text version of this page in [Pandoc Markdown] format [Fedora 12 Virtual Machine]: worksheet07.html [GRUB Configuration File]: assignment11.html [`sudo`]: assignment12.html [Course Linux Server]: 010_course_linux_server.html [Checking Program]: #checking-marking-and-submitting-your-work [Booting and GRUB]: 750_booting_and_grub.html [Tasks]: #tasks [CST8207 GNU/Linux Operating Systems I]: indexcgi.cgi [Worksheet #13 ODT]: worksheet13.odt [Worksheet #13 PDF]: worksheet13.pdf [File Transfer]: 015_file_transfer.html [1]: 750_booting_and_grub.html#legacy-run-levels-and-services [redirect standard error]: 200_redirection.html [Source Directory]: #the-source-directory [Symbolic Link]: 460_symbolic_links.html [Search Path]: 400_search_path.html [Plain Text]: assignment13.txt [Pandoc Markdown]: http://johnmacfarlane.net/pandoc/