COMP2021 Lab2: More Linux Utilities

Remote access Lab2 (Room 4214)

Windows: SSH Secure Shell (user guide); Putty

Unix (e.g. MacOS/Linux etc.) SSH command:

Read the man pages

Read the lecture notes and man pages of the following commands:

Lab2 will help you get to know more about basic settings and utilities in linux system in order to strengthen your programming muscles under linux environment for future use. In each of the following task, learn by either web searching, manual pages or other methods you prefer to get yourself familiar with the material and find solutions to given problems.

  1. Editor War VIM/EMACS

    Download the file comp2021.txt into your home directory. Now Edit your copy of the document using vim.
    1. Remove the extra "culture" in the 1st paragraph.
    2. Add the words "LOL!" to the end of the second paragraph.
    3. Replace all occurrences of "unix" with "Unix".
    4. Find the line containing "vim", replace all "emacs" with "emacs-bad-editor".
    5. Save the file and quit.

    Repeat the same exercise with emacs (Maybe this time you can replace "vim" with "vim-bad-editor".).

    Get to know more about Vim and Emacs by reading manual pages or online searing. They are both powerful tools after you get familiar with them.

  2. Multiple ways of changing your file permissions

    Solution 1: chmod by numerical values

    # Permission rwx
    7 full 111
    6 read and write 110
    5 read and execute 101
    4 read only 100
    3 write and execute 011
    2 write only 010
    1 execute only 001
    0 none 000

    Solution 2: chmod by target modification/assignment

    Reference Class Description
    u user the owner of the file
    g group users who are members of the file's group
    o others users who are neither the owner of the file nor members of the file's group
    a all all three of the above, same as ugo 
    Create some file called test. Put single-line-commands modifying the test in lab2.txt that 
1. Add read permission for all.
2. Give read and write permission to the owner, while all permissions are cleared for the group and others.
3. Use numerical value assignments to set read and write and no execution access for the owner and group, 
and read, no write, no execute for all others.

  3. Explore file access permission

    Check your user group by command id. Find out what groups you are in.

    Team up with one or two classmates. Can you access others' home directory? In what way can you make your home directory private/public for reading? Use chmod properly which you just learnt about. 

    Together with your group mate, explore the following situations.
1. First run chmod 755 ~ so that your partner could access and see your files in your home directory. Create 
   a file called test under it. Give (your partner) permission to write to the file test. Now can your partner 
   modify the file? 
2. Now retract the permission to write to this file. However give permission to write to your home directory. 
   Can your partner modify the file?
3. Deny the permission to write to your home directory. Create a directory under your home directory called 
   test_directory. Give permission to both access it and write to it. Now under this test_directory create 
   another file named test2. Make sure the permission to write to this file is denied. 
   Now in this case can your partner modify the file test2?
4. In this last case, shut down the write permission to write to test_directory, however, give permission to write 
   to home directory. In this case an your partner modify the file test2?

  4. Many shells are equipped with powerful job control mechanism to handle many running jobs (i.e. processes) in parallel. First follow the demo by TA to get a brief understanding of job control:

    You can pause a job using Ctrl+Z and turn to do something else without quitting.

    Jobs can be in foreground or background. There will be only one job in foreground -- the job interacts with your shell - it receives input from keyboard and sends output to the screen. One is capable of managing jobs in foreground and background using command fg, bg.

    Conceptual difference between processes and jobs: ps and jobs commands.

    One could kill a job/process by job ID, process ID, or even name. 

    Read manual pages and get to know about command sleep. 
1. Run sleep 200 in foreground, suspend it and then put it into background. Show both the job number and PID of this job. At last bring the job back to foreground.
2. Run sleep 300 directly in background, and then use kill to terminate the process by its job number. 
3. Repeat, however this time kill by its PID instead.
4. Open up some webpages using Firefox. Now kill all of them using kill command.

Lab Answers

Please find the answers for lab 2: anslab2.txt.

Any inquiry please contact your TA by email