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updates the linuxfun ex

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certificates/essentials/exercises_linuxfun.md
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@ -10,11 +10,11 @@
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.
5. Execute: `alias rm='rm -i'` . Test your alias with a test file. Does this work as expected?
6. List all current aliases.
7a. Create an alias called `city` that echoes your hometown.
7b. Use your alias to test that it works.
7. Create an alias called `city` that echoes your hometown.
7. Use your alias to test that it works.
8. Execute `set -x` to display shell expansion for every command.
9. Test the functionality of `set -x` by executing your city and rm aliases.
10 Execute `set +x` to stop displaying shell expansion.
10. Execute `set +x` to stop displaying shell expansion.
11. Remove your city alias.
12. What is the location of the `cat` and the `passwd` commands?
13. Explain the difference between the following commands:
@ -189,20 +189,22 @@
1. Write a script that receives four parameters, and outputs them in reverse order.
2. Write a script that receives two parameters (two filenames) and outputs whether those files exist.
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.
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.
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`.
## 26.6. practice : more scripting
1. Write a script that asks for two numbers, and outputs the sum and product (as shown here).
Enter a number: 5
Enter another number: 2
```
Enter a number: 5
Enter another number: 2
Sum: 5 + 2 = 7
Product: 5 x 2 = 10
Sum: 5 + 2 = 7
Product: 5 x 2 = 10
```
2. Improve the previous script to test that the numbers are between 1 and 100, exit with an error if necessary.
3. Improve the previous script to congratulate the user if the sum equals the product.
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.
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.
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.
## 27.15. practice: introduction to users
@ -210,37 +212,37 @@
2. Display a list of all logged on users.
3. Display a list of all logged on users including the command they are running at this very moment.
4. Display your user name and your unique user identification (userid).
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.
6. Now use su - to switch to another user and notice the difference. Note that su - gets you into the home directory of Tania.
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.
6. Now use `su -` to switch to another user and notice the difference. Note that `su -` gets you into the home directory of Tania.
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.)
8. Now try the same, but with sudo before your command.
8. Now try the same, but with `sudo` before your command.
## 28.13. practice: user management
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.
2. Create a user named venus, including home directory, bash shell, a description that reads Venus Williams all in one single command.
3. Verify that both users have correct entries in /etc/passwd, /etc/shadow and /etc/group.
3. Verify that both users have correct entries in `/etc/passwd`, `/etc/shadow` and `/etc/group`.
4. Verify that their home directory was created.
5. Create a user named einstime with /bin/date as his default logon shell.
5. Create a user named einstime with `/bin/date` as his default logon shell.
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 ?
8. Create a file named welcome.txt and make sure every new user will see this file in their home directory.
8. Create a file named `welcome.txt` and make sure every new user will see this file in their home directory.
9. Verify this setup by creating (and deleting) a test user account.
10. Change the default login shell for the serena user to /bin/bash. Verify before and after you make this change.
10. Change the default login shell for the serena user to `/bin/bash`. Verify before and after you make this change.
## 29.10. practice: user passwords
1. Set the password for serena to hunter2.
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.
3. Use passwd -d to disable the serena password. Verify the serena line in /etc/shadow before and after disabling.
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?
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.
3. Use `passwd -d` to disable the serena password. Verify the serena line in `/etc/shadow` before and after disabling.
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`?
5. Try changing the password of serena to serena as serena.
6. Make sure serena has to change her password in 10 days.
7. Make sure every new user needs to change their password every 10 days.
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 ?
9. Why use vipw instead of vi ? What could be the problem when using vi or vim ?
10. Use chsh to list all shells (only works on RHEL/CentOS/Fedora), and compare to cat /etc/shells.
11. Which useradd option allows you to name a home directory ?
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.
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 ?
9. Why use `vipw` instead of `vi`? What could be the problem when using `vi` or `vim`?
10. Use `chsh` to list all shells (only works on RHEL/CentOS/Fedora), and compare to `cat /etc/shells`.
11. Which `useradd` option allows you to name a home directory?
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`.
## 30.9. practice: user profiles
@ -249,55 +251,55 @@
3. Put a unique variable, alias and function in each of those files.
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.
5. Do you also know the order in which they are executed?
6. When an application depends on a setting in $HOME/.profile, does it matter whether $HOME/.bash_profile exists or not ?
6. When an application depends on a setting in `$HOME/.profile`, does it matter whether `$HOME/.bash_profile` exists or not?
## 31.10. practice: groups
1. Create the groups tennis, football and sports.
2. In one command, make venus a member of tennis and sports.
3. Rename the football group to foot.
4. Use vi to add serena to the tennis group.
5. Use the id command to verify that serena is a member of tennis.
4. Use `vi` to add serena to the tennis group.
5. Use the `id` command to verify that serena is a member of tennis.
6. Make someone responsible for managing group membership of foot and sports. Test that it works.
## 32.4. practice: standard file permissions
1. As normal user, create a directory ~/permissions. Create a file owned by yourself in there.
2. Copy a file owned by root from /etc/ to your permissions dir, who owns this file now ?
3. As root, create a file in the users ~/permissions directory.
1. As normal user, create a directory `~/permissions`. Create a file owned by yourself in there.
2. Copy a file owned by root from `/etc/` to your permissions dir, who owns this file now ?
3. As root, create a file in the users `~/permissions` directory.
4. As normal user, look at who owns this file created by root.
5. Change the ownership of all files in ~/permissions to yourself.
5. Change the ownership of all files in `~/permissions` to yourself.
6. Make sure you have all rights to these files, and others can only read.
7. With chmod, is 770 the same as rwxrwx--- ?
8. With chmod, is 664 the same as r-xr-xr-- ?
9. With chmod, is 400 the same as r-------- ?
10. With chmod, is 734 the same as rwxr-xr-- ?
11a. Display the umask in octal and in symbolic form.
11b. Set the umask to 077, but use the symbolic format to set it. Verify that this works.
7. With `chmod`, is 770 the same as rwxrwx--- ?
8. With `chmod`, is 664 the same as r-xr-xr-- ?
9. With `chmod`, is 400 the same as r-------- ?
10. With `chmod`, is 734 the same as rwxr-xr-- ?
11. Display the `umask` in octal and in symbolic form.
11. Set the `umask` to 077, but use the symbolic format to set it. Verify that this works.
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.
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.
13b. Can root read this file ? Can root write to this file with vi ?
13. 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`.
13. Can root read this file ? Can root write to this file with `vi`?
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.
## 33.5. practice: sticky, setuid and setgid bits
1a. Set up a directory, owned by the group sports.
1b. Members of the sports group should be able to create files in this directory.
1c. All files created in this directory should be group-owned by the sports group.
1d. Users should be able to delete only their own user-owned files.
1e. Test that this works!
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.
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.
1. Set up a directory, owned by the group sports.
1. Members of the sports group should be able to create files in this directory.
1. All files created in this directory should be group-owned by the sports group.
1. Users should be able to delete only their own user-owned files.
1. Test that this works!
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.
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.
## 35.6. practice: links
1. Create two files named winter.txt and summer.txt, put some text in them.
2. Create a hard link to winter.txt named hlwinter.txt.
1. Create two files named `winter.txt` and `summer.txt`, put some text in them.
2. Create a hard link to `winter.txt` named `hlwinter.txt`.
3. Display the inode numbers of these three files, the hard links should have the same inode.
4. Use the find command to list the two hardlinked files
4. Use the `find` command to list the two hardlinked files
5. Everything about a file is in the inode, except two things : name them!
6. Create a symbolic link to summer.txt called slsummer.txt.
6. Create a symbolic link to `summer.txt` called `slsummer.txt`.
7. Find all files with inode number 2. What does this information tell you ?
8. Look at the directories /etc/init.d/ /etc/rc2.d/ /etc/rc3.d/ ... do you see the links ?
9. Look in /lib with ls -l...
10. Use find to look in your home directory for regular files that do not(!) have one hard link.
8. Look at the directories `/etc/init.d/` `/etc/rc2.d/` `/etc/rc3.d/` ... do you see the links ?
9. Look in `/lib` with `ls -l`...
10. Use `find` to look in your home directory for regular files that do not(!) have one hard link.