3.1 The Source Directory

All references to the “Source Directory” below are to the CLS directory ~idallen/cst8177/14f/assignment01/ 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 (seven letters).

4.1 Set Up – The Base Directory on the CLS

1. Do a Remote Login to the Course Linux Server (CLS) from any existing computer, using the host name appropriate for whether you are on-campus or off-campus. Pay particular attention to the special non-Algonquin password you must use, or else you will lock yourself out of the machine. All work in this assignment must be done on the CLS.

2. Create the following directory structure in your CLS HOME directory and record (for study purposes) the series of Unix commands you used to create it. Spelling and capitalization must be exactly as shown:

   CST8177-14F
   `-- Assignments
       `-- assignment01

   This directory is the base directory for most pathnames in this assignment. Store your files and answers here.

3. There is a Checking Program named assignment01check in the Source Directory on the CLS. Follow the instructions in the first two steps at the start of Checking Program to create a working symbolic link to this program.

4. If you haven’t taken the prerequisite course CST8207 GNU/Linux Operating Systems I using the CLS, you will need to read Startup Files to know what lines to place in your .bash_profile and .bashrc before beginning this assignment.

Check your work so far using the assignment01check program symlink.

4.2 Simple Tasks

1. From your HOME directory, use the ls command with options to give a long listing (showing permissions), include all hidden files, include inode numbers, and recursively include all subdirectories. (Do not use any other options.) When the output is correct, redirect the output of this command into new file listing_start.txt under assignment01 – it will be at least 16 lines of output. (If you have files from other terms in your account, you may get some “permission denied” errors doing the listing [ignore the errors] and the number will be many more than 16 lines.)

2. Run the whoami command. When the output is correct, redirect the output of this command into new file whoami.txt under assignment01

3. Run the id command. When the output is correct, append the output of this command to existing file whoami.txt under assignment01. (Note the word append). The file must now have two lines of output in it. Check it!

4. Rename the file whoami.txt to have the new name whoamiid.txt (in the same directory) and make extra sure you spelled the new name correctly.

5. Use a command to count only the number of lines (not characters or words) in file read.txt in the Source Directory, using the absolute pathname of the file. (You’ll know you have the right file if the size is 838 characters.) When the output is correct (one line), redirect the output of this command (the output containing only the line count number and the absolute pathname, not any other numbers) into new file readlines.txt under assignment01

6. Use a command to search for and display the single line containing the exact text phrase “permissions is useless” located inside any one of the text files (files having a .txt file extension) located in the notes/ directory of the previous term CST8207 (14W: Winter 2014). The Introduction and Overview explains where to find these notes and how to search them, just as you did last term. When the output is correct, redirect the one line of output of this command into new file useless.txt under assignment01 The file should be one line long.

Check your work so far using the assignment01check program symlink.

4.3 File Permission Tasks

1. Copy the binary program file /bin/hostname three times to files named read_only, write_only, and execute_only under your assignment01 directory. This is a BINARY program file, so do not display the content of the file on your terminal screen!

2. Change the permissions on all three copied files so that group and other have no permissions. (You can do this with one command name and a file GLOB pattern.)

3. Change the permissions on the read_only file so that only you can read the file but not write or execute the file.
   1. Verify readability of the file by using any command that reads the content of the file. For example, you can word count the file or try to copy the file to /dev/null.
   2. Verify non-writability by attempting to overwrite the file. Attempts to overwrite should fail with “permission denied”.
   3. Verify non-executability by attempting to execute the file as a program. It should fail with “permission denied”. (You may need to review how to execute a file using a pathname. The error must be “permission denied” not “no such file” or “command not found”.)
4. Change the permissions on the write_only file so that only you can write (including append to) the file but not read or execute the file.
   1. Using operations similar to the previous file, verify that you can write the file but not read or execute it.
5. Change the permissions on the execute_only file so that only you can execute the file but not read or write the file.
   1. Using operations similar to the previous files, verify that you can execute the file but not read or write it.

Check your work so far using the assignment01check program symlink.

4.4 Directory Permission Tasks

1. Make the following directory structure under assignment01/

   permissions/
   permissions/read_only/
   permissions/write_only/
   permissions/execute_only/

2. Change the permissions on the permissions/ directory so the owner (you) can read, write, and search, but group and other have no permissions.

3. Change the permissions on all three subdirectories of permissions/ so that that group and other have no permissions. (You can do this with one command name and a file GLOB pattern.)

4. Change the permissions on read_only/ so that you can see the names in the directory (with echo read_only/* or similar), but cannot take an accurate long listing, and cannot create files, and cannot cd into the directory. (Verify that you can/cannot do these things!)

   Hint: Of course echo read_only/* will only show file names if you actually create those files.

5. Change the permissions on write_only/ so that you cannot see the names in the directory, but you can add new files to the directory, delete files from the directory, and cd into the directory. (Verify that you can/cannot do these things!)

6. Change the permissions on execute_only/ so that you can (only) cd into the directory. You cannot see the names in the directory or add or delete files from the directory. Verify!

Check your work so far using the assignment01check program symlink.

4.5 Finding files in a maze

1. Under the Source Directory there is a directory named maze (four letters). This maze contains many hidden sub-directories. Use a single command (no pipes needed) to find in the maze a single hidden file with a basename similar to .abcd0001*txt, but look for the basename that starts with a period followed by your own Blackboard userid, not the fake userid abcd0001. To look for the file, replace the string abcd0001 in .abcd0001*txt with your own userid before you look. The basename you find must be exactly 13 characters long and contain a period and a real asterisk. It must have no leading or trailing blanks around it.

   Hint#1: You might want to use a single command (not a pipeline) that finds files by basename to do this. (Do not try to use cd and ls to find your file; the maze is really big.)

   Hint#2: If you want to find a name containing a real asterisk, you may need to escape the asterisk to stop it from being used as a pattern character (wildcard), and you need to do this both for the shell that reads your command line and for the command that finds the files. if you get the escaping right, you will find exactly one file.

2. When you find the right file basename (there is only one for your userid), put its shortest full absolute pathname into new file foundmaze.txt under your assignment01 directory. Note: Shortest absolute pathnames contain no /./ or /../ or tilde (“~”) expressions; simplify the path to the shortest possible absolute pathname.

Check your work so far using the assignment01check program symlink.

4.6 Symbolic Link Tasks

1. Create an absolute path soft Symbolic Link to the Linux password file:
   • Create the absolute path symlink under your assignment01 directory.
   • Name the symlink thepasswd
   • The text of the symlink should be an absolute pathname to the password file.
   • Verify that you can read the password file using the thepasswd symbolic link, e.g. wc thepasswd must give exactly the same output as for the password file.

   Display the file attributes and inode numbers of both the password file and the thepasswd symbolic link, and confirm that they are different. Unlike a hard link, a symbolic link is a separate inode.

2. Make a new relative path soft link to the thepasswd symlink you just created:
   • Create the relative path symlink under your assignment01 directory.
   • Name the symlink alsopasswd
   • The text of the symlink should be the shortest relative pathname to thepasswd in the same directory. (See the Hint below.)
   • If you are successful, relative symlink alsopasswd now links to absolute symlink thepasswd that links to the password file.
   • Verify that you can read the password file using the alsopasswd symbolic link, e.g. wc alsopasswd must work as expected.

   Hint: All of “././foo” and “./foo” and “foo” are relative pathnames that lead to the same place. Which one is the shortest? Always use the shortest relative pathname. Don’t use ./foo when all you need is foo.

3. Rename the thepasswd symlink to be otherpasswd.
   • Now, symlink alsopasswd is a broken relative symlink to a non-existent thepasswd symlink.
   • Confirm that you can no longer use alsopasswd to read the text of the password file, e.g. wc alsopasswd no longer works.

   Definition: A broken or dangling symlink is a symlink to something that doesn’t exist. The alsopasswd symlink is now a dangling symlink, since it links to the nonexistent thepasswd.

Check your work so far using the assignment01check program symlink.

4.7 Hard Link Tasks

1. Create a hard link to the read.txt file in the Source Directory (you counted the lines in this file earlier); name the hard link hardlink in the assignment01 directory. (Note; On some versions of Unix/Linux, you are not allowed to hard link to a file you cannot write. That protection has been disabled on the CLS.) Verify that you can read the file using the hardlink hard link.

   Display the file attributes and inode numbers of both the read.txt file and the hardlink hard link, and confirm that they are identical. (Only the pathnames will be different.) These hard links are just two names for the same file inode.

2. Make a new hard link to hardlink named newhard in the same assignment01 directory.

   Display the file attributes and inode numbers of the read.txt file and both the new hard link files, and confirm that all three are identical. (Only the pathnames will be different.) These hard links are just three names for the same file inode.

3. Rename hardlink to junkread and note that this does not break the hard link for newhard. Verify that all three files have the same attributes and inode numbers and that you can read the text of the read.txt file through both hard links, as before.

Check your work so far using the assignment01check program symlink.

4.8 Finishing Tasks

1. Make a backup copy of your listing_start.txt file, in case you accidentally overwrite it in the next step.

2. From the same starting directory, repeat the command you used to create listing_start.txt at the beginning of this lab, but redirect the output this time into the file listing_end.txt in the same directory as listing_start.txt, and make sure that all errors (standard error output) also go into the output file and not on the screen.

   Hints: The first five words in the previous paragraph are very important. You might find your shell history useful here. There is a special syntax to also redirect error messages into a file using Shell I/O Redirection.

3. Use the diff command to compare the earlier listing file to the previous one you did before starting this lab. Note the many changes!

4.9 When you are done

That is all the tasks you need to do.

Check your work a final time using the Checking Program and save the output as described below. Submit your mark following the directions below.