304 lines
19 KiB
Markdown
304 lines
19 KiB
Markdown
# Linuxfun exercises
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**Taken from [this](http://linux-training.be/linuxfun.pdf) pdf**
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## 12.9. practice: commands and arguments
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1. How many arguments are in this line (not counting the command itself). `touch '/etc/cron/cron.allow' 'file 42.txt' "file 33.txt"`
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2. Is `tac` a shell builtin command ?
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3. Is there an existing alias for `rm`?
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4. Read the man page of `rm`, make sure you understand the `-i` option of rm. Create and remove a file to test the -i option.
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5. Execute: `alias rm='rm -i'` . Test your alias with a test file. Does this work as expected?
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6. List all current aliases.
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7a. Create an alias called `city` that echoes your hometown.
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7b. Use your alias to test that it works.
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8. Execute `set -x` to display shell expansion for every command.
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9. Test the functionality of `set -x` by executing your city and rm aliases.
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10 Execute `set +x` to stop displaying shell expansion.
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11. Remove your city alias.
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12. What is the location of the `cat` and the `passwd` commands?
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13. Explain the difference between the following commands:
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* `echo`
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* `/bin/echo `
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14. Explain the difference between the following commands:
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* `echo Hello`
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* `echo -n Hello `
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15. Display A B C with two spaces between B and C.
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16. (optional) Complete the following command (do not use spaces) to display exactly the following output:
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```
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4+4 =8
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10+14 =24
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```
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17. Use `echo` to display the following exactly: `??\\`
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## 13.9. practice: control operators
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0. Each question can be answered by one command line!
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1. When you type `passwd`, which file is executed?
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2. What kind of file is that?
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3. Execute the `pwd` command twice. (remember 0.)
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4. Execute `ls` after `cd /etc`, but only if `cd /etc` did not error.
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5. Execute `cd /etc` after `cd etc,` but only if `cd etc` fails.
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6. Echo `it worked` when `touch test42` works, and echo `it failed` when the touch failed. All on one command line as a normal user (not root). Test this line in your home directory and in `/bin/`.
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7. Execute `sleep 6`, what is this command doing ?
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8. Execute `sleep 200` in background (do not wait for it to finish).
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9. Write a command line that executes `rm file55`. Your command line should print `success` if file55 is removed, and print `failed` if there was a problem.
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10. (optional) Use echo to display `"Hello World with strange' characters \ * [ } ~ \ \ ."` (including all quotes)
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## 14.13. practice: shell variables
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1. Use echo to display `Hello` followed by your `username`. (use a bash variable!)
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2. Create a variable `answer` with a value of 42.
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3. Copy the value of `$LANG` to `$MyLANG`.
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4. List all current shell variables.
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5. List all exported shell variables.
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6. Do the `env` and `set` commands display your variable?
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6. Destroy your answer variable.
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7. Create two variables, and export one of them.
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8. Display the exported variable in an interactive child shell.
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9. Create a variable, give it the value `Dumb`, create another variable with value `do`. Use `echo` and the two variables to `echo Dumbledore`.
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10. Find the list of backslash escaped characters in the manual of bash. Add the time to your PS1 prompt.
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## 15.3. practice: shell embedding
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1. Find the list of shell options in the man page of bash. What is the difference between `set -u` and `set -o nounset`?
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2. Activate `nounset` in your shell. Test that it shows an error message when using non-existing variables.
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3. Deactivate `nounset`.
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4. Execute `cd /var` and `ls` in an embedded shell. The echo command is only needed to show the result of the ls command. Omitting will result in the shell trying to execute the first file as a command.
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5. Create the variable `embvar` in an embedded shell and echo it. Does the variable exist in your current shell now ?
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6. Explain what `set -x` does. Can this be useful ?
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7. (optional) Given the following screenshot, add exactly four characters to that command line so that the total output is `FirstMiddleLast`. `[paul@RHEL4b ~]$ echo First; echo Middle; echo Last`
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8. Display a long listing (`ls -l`) of the `passwd` command using the `which` command inside an embedded shell.
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## 16.12. practice: shell history
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1. Issue the command `echo The answer to the meaning of life, the universe and everything is 42.`.
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2. Repeat the previous command using only two characters (there are two solutions!)
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3. Display the last 5 commands you typed.
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4. Issue the long echo from question 1 again, using the line numbers you received from the command in question 3.
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5. How many commands can be kept in memory for your current shell session?
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6. Where are these commands stored when exiting the shell?
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7. How many commands can be written to the history file when exiting your current shell session?
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8. Make sure your current bash shell remembers the next 5000 commands you type.
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9. Open more than one console (by press Ctrl-shift-t in gnome-terminal, or by opening an extra putty.exe in MS Windows) with the same user account. When is command history written to the history file ?
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## 17.7. practice: shell globbing
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1. Create a test directory and enter it.
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2. Create the following files : (the last one has 6 characters including a space)
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* `file1`
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* `file10`
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* `file11`
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* `file2`
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* `File2`
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* `File3`
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* `file33`
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* `fileAB`
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* `filea`
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* `fileA`
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* `fileAAA`
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* `file(`
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* `file 2`
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3. List (with ls) all files starting with file
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4. List (with ls) all files starting with File
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5. List (with ls) all files starting with file and ending in a number.
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6. List (with ls) all files starting with file and ending with a letter
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7. List (with ls) all files starting with File and having a digit as fifth character.
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8. List (with ls) all files starting with File and having a digit as fifth character and nothing else.
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9. List (with ls) all files starting with a letter and ending in a number.
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10. List (with ls) all files that have exactly five characters.
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11. List (with ls) all files that start with f or F and end with 3 or A.
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12. List (with ls) all files that start with f have i or R as second character and end in a number.
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13. List all files that do not start with the letter F.
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14. Copy the value of `$LANG` to `$MyLANG`.
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15. Show the influence of `$LANG` in listing A-Z or a-z ranges.
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16. You receive information that one of your servers was cracked, the cracker probably replaced the `ls` command. You know that the `echo` command is safe to use. Can echo replace ls ? How can you list the files in the current directory with echo?
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17. Is there another command besides `cd` to change directories?
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## 18.9. practice: input/output redirection
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1. Activate the `noclobber` shell option.
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2. Verify that `noclobber` is active by repeating an `ls` on `/etc/` with redirected output to a file.
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3. When listing all shell options, which character represents the `noclobber` option ?
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4. Deactivate the `noclobber` option.
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5. Make sure you have two shells open on the same computer. Create an empty tailing.txt file. Then type `tail -f tailing.txt`. Use the second shell to append a line of text to that file. Verify that the first shell displays this line.
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6. Create a file that contains the names of five people. Use `cat` and output redirection to create the file and use a here document to end the input.
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## 19.13. practice: filters
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1. Put a sorted list of all bash users in `bashusers.txt`.
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2. Put a sorted list of all logged on users in `onlineusers.txt`.
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3. Make a list of all filenames in `/etc` that contain the string `conf` in their filename.
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4. Make a sorted list of all files in `/etc` that contain the case insensitive string `conf` in their filename.
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5. Look at the output of `/sbin/ifconfig`. Write a line that displays only ip address and the subnet mask.
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6. Write a line that removes all non-letters from a stream.
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7. Write a line that receives a text file, and outputs all words on a separate line.
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8. Write a spell checker on the command line. (There may be a dictionary in `/usr/share/dict/`.)
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## 20.11. practice: basic Unix tools
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1. Explain the difference between these two commands. This question is very important. If you don't know the answer, then look back at the shell chapter.
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* `find /data -name "*.txt"`
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* `find /data -name *.txt`
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2. Explain the difference between these two statements. Will they both work when there are 200 .odf files in /data ? How about when there are 2 million .odf files ?
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* `find /data -name "*.odf" > data_odf.txt`
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* `find /data/*.odf > data_odf.txt`
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3. Write a find command that finds all files created after January 30th 2010.
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4. Write a find command that finds all `*.odf` files created in September 2009.
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5. Count the number of `*.conf` files in /etc and all its subdirs.
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6. Here are two commands that do the same thing: copy `*.odf` files to /backup/ . What would be a reason to replace the first command with the second ? Again, this is an important question.
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* `cp -r /data/*.odf /backup/`
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* `find /data -name "*.odf" -exec cp {} /backup/ \;`
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7. Create a file called `loctest.txt`. Can you find this file with `locate`? Why not? How do you make locate find this file ?
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8. Use `find` and `-exec` to rename all .htm files to .html.
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9. Issue the `date` command. Now display the date in YYYY/MM/DD format.
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10. Issue the `cal` command. Display a calendar of 1582 and 1752. Notice anything special ?
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## 22.19. practice: vi(m)
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1. Start the `vimtutor` and do some or all of the exercises. You might need to run `aptitude install vim` on xubuntu.
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2. What 3 key sequence in command mode will duplicate the current line.
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3. What 3 key sequence in command mode will switch two lines' place (line five becomes line six and line six becomes line five).
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4. What 2 key sequence in command mode will switch a character's place with the next one.
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5. vi can understand macro's. A macro can be recorded with q followed by the name of the macro. So qa will record the macro named a. Pressing q again will end the recording. You can recall the macro with @ followed by the name of the macro. Try this example: i 1 'Escape Key' qa yyp 'Ctrl a' q 5@a (Ctrl a will increase the number with one).
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6. Copy `/etc/passwd` to your `~/passwd`. Open the last one in vi and press Ctrl v. Use the arrow keys to select a Visual Block, you can copy this with y or delete it with d. Try pasting it.
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7. What does dwwP do when you are at the beginning of a word in a sentence ?
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## 23.9. practice: introduction to scripting
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0. Give each script a different name, keep them for later!
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1. Write a script that outputs the name of a city.
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2. Make sure the script runs in the bash shell.
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3. Make sure the script runs in the Korn shell.
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4. Create a script that defines two variables, and outputs their value.
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5. The previous script does not influence your current shell (the variables do not exist outside of the script). Now run the script so that it influences your current shell.
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6. Is there a shorter way to source the script ?
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7. Comment your scripts so that you know what they are doing.
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## 24.7. practice: scripting tests and loops
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1. Write a script that uses a for loop to count from 3 to 7.
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2. Write a script that uses a for loop to count from 1 to 17000.
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3. Write a script that uses a while loop to count from 3 to 7.
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4. Write a script that uses an until loop to count down from 8 to 4.
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5. Write a script that counts the number of files ending in .txt in the current directory.
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6. Wrap an if statement around the script so it is also correct when there are zero files ending in .txt.
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## 25.7. practice: parameters and options
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1. Write a script that receives four parameters, and outputs them in reverse order.
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2. Write a script that receives two parameters (two filenames) and outputs whether those files exist.
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3. Write a script that asks for a filename. Verify existence of the file, then verify that you own the file, and whether it is writable. If not, then make it writable.
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4. Make a configuration file for the previous script. Put a logging switch in the config file, logging means writing detailed output of everything the script does to a log file in /tmp.
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## 26.6. practice : more scripting
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1. Write a script that asks for two numbers, and outputs the sum and product (as shown here).
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Enter a number: 5
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Enter another number: 2
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Sum: 5 + 2 = 7
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Product: 5 x 2 = 10
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2. Improve the previous script to test that the numbers are between 1 and 100, exit with an error if necessary.
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3. Improve the previous script to congratulate the user if the sum equals the product.
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4. Write a script with a case insensitive case statement, using the shopt nocasematch option. The nocasematch option is reset to the value it had before the scripts started.
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5. If time permits (or if you are waiting for other students to finish this practice), take a look at Linux system scripts in /etc/init.d and /etc/rc.d and try to understand them. Where does execution of a script start in /etc/init.d/samba ? There are also some hidden scripts in ~, we will discuss them later.
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## 27.15. practice: introduction to users
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1. Run a command that displays only your currently logged on user name.
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2. Display a list of all logged on users.
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3. Display a list of all logged on users including the command they are running at this very moment.
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4. Display your user name and your unique user identification (userid).
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5. Use su to switch to another user account (unless you are root, you will need the password of the other account). And get back to the previous account.
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6. Now use su - to switch to another user and notice the difference. Note that su - gets you into the home directory of Tania.
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7. Try to create a new user account (when using your normal user account). this should fail. (Details on adding user accounts are explained in the next chapter.)
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8. Now try the same, but with sudo before your command.
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## 28.13. practice: user management
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1. Create a user account named serena, including a home directory and a description (or comment) that reads Serena Williams. Do all this in one single command.
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2. Create a user named venus, including home directory, bash shell, a description that reads Venus Williams all in one single command.
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3. Verify that both users have correct entries in /etc/passwd, /etc/shadow and /etc/group.
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4. Verify that their home directory was created.
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5. Create a user named einstime with /bin/date as his default logon shell.
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7. What happens when you log on with the einstime user ? Can you think of a useful real world example for changing a user's login shell to an application ?
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8. Create a file named welcome.txt and make sure every new user will see this file in their home directory.
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9. Verify this setup by creating (and deleting) a test user account.
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10. Change the default login shell for the serena user to /bin/bash. Verify before and after you make this change.
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## 29.10. practice: user passwords
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1. Set the password for serena to hunter2.
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2. Also set a password for venus and then lock the venus user account with usermod. Verify the locking in /etc/shadow before and after you lock it.
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3. Use passwd -d to disable the serena password. Verify the serena line in /etc/shadow before and after disabling.
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4. What is the difference between locking a user account and disabling a user account's password like we just did with usermod -L and passwd -d?
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5. Try changing the password of serena to serena as serena.
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6. Make sure serena has to change her password in 10 days.
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7. Make sure every new user needs to change their password every 10 days.
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8. Take a backup as root of /etc/shadow. Use vi to copy an encrypted hunter2 hash from venus to serena. Can serena now log on with hunter2 as a password ?
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9. Why use vipw instead of vi ? What could be the problem when using vi or vim ?
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10. Use chsh to list all shells (only works on RHEL/CentOS/Fedora), and compare to cat /etc/shells.
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11. Which useradd option allows you to name a home directory ?
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12. How can you see whether the password of user serena is locked or unlocked ? Give a solution with grep and a solution with passwd.
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## 30.9. practice: user profiles
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1. Make a list of all the profile files on your system.
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2. Read the contents of each of these, often they source extra scripts.
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3. Put a unique variable, alias and function in each of those files.
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4. Try several different ways to obtain a shell (su, su -, ssh, tmux, gnome-terminal, Ctrl- alt-F1, ...) and verify which of your custom variables, aliases and function are present in your environment.
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5. Do you also know the order in which they are executed?
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6. When an application depends on a setting in $HOME/.profile, does it matter whether $HOME/.bash_profile exists or not ?
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## 31.10. practice: groups
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1. Create the groups tennis, football and sports.
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2. In one command, make venus a member of tennis and sports.
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3. Rename the football group to foot.
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4. Use vi to add serena to the tennis group.
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5. Use the id command to verify that serena is a member of tennis.
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6. Make someone responsible for managing group membership of foot and sports. Test that it works.
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## 32.4. practice: standard file permissions
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1. As normal user, create a directory ~/permissions. Create a file owned by yourself in there.
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2. Copy a file owned by root from /etc/ to your permissions dir, who owns this file now ?
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3. As root, create a file in the users ~/permissions directory.
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4. As normal user, look at who owns this file created by root.
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5. Change the ownership of all files in ~/permissions to yourself.
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6. Make sure you have all rights to these files, and others can only read.
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7. With chmod, is 770 the same as rwxrwx--- ?
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8. With chmod, is 664 the same as r-xr-xr-- ?
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9. With chmod, is 400 the same as r-------- ?
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10. With chmod, is 734 the same as rwxr-xr-- ?
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11a. Display the umask in octal and in symbolic form.
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11b. Set the umask to 077, but use the symbolic format to set it. Verify that this works.
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12. Create a file as root, give only read to others. Can a normal user read this file ? Test writing to this file with vi.
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13a. Create a file as normal user, give only read to others. Can another normal user read this file ? Test writing to this file with vi.
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13b. Can root read this file ? Can root write to this file with vi ?
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14. Create a directory that belongs to a group, where every member of that group can read and write to files, and create files. Make sure that people can only delete their own files.
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## 33.5. practice: sticky, setuid and setgid bits
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1a. Set up a directory, owned by the group sports.
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1b. Members of the sports group should be able to create files in this directory.
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1c. All files created in this directory should be group-owned by the sports group.
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1d. Users should be able to delete only their own user-owned files.
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1e. Test that this works!
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2. Verify the permissions on /usr/bin/passwd. Remove the setuid, then try changing your password as a normal user. Reset the permissions back and try again.
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3. If time permits (or if you are waiting for other students to finish this practice), read about file attributes in the man page of chattr and lsattr. Try setting the i attribute on a file and test that it works.
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## 35.6. practice: links
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1. Create two files named winter.txt and summer.txt, put some text in them.
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2. Create a hard link to winter.txt named hlwinter.txt.
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3. Display the inode numbers of these three files, the hard links should have the same inode.
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4. Use the find command to list the two hardlinked files
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5. Everything about a file is in the inode, except two things : name them!
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6. Create a symbolic link to summer.txt called slsummer.txt.
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7. Find all files with inode number 2. What does this information tell you ?
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8. Look at the directories /etc/init.d/ /etc/rc2.d/ /etc/rc3.d/ ... do you see the links ?
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9. Look in /lib with ls -l...
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10. Use find to look in your home directory for regular files that do not(!) have one hard link.
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