diff --git a/modules/resources/solution_raspberrypi.md b/modules/resources/solution_raspberrypi.md new file mode 100644 index 0000000..f239889 --- /dev/null +++ b/modules/resources/solution_raspberrypi.md @@ -0,0 +1,271 @@ +# The FTP challenge + +## Getting the file + +The first step to solving this exersise is to download the CSV file to your Raspberry. +For those wondering what on earth a CSV file is I invite you to a detailed [read](https://en.wikipedia.org/wiki/Comma-separated_values) but to make a long story short it stands for *comma separated values* and is one of the most basic ways to structure data. +You can use Libreoffice calc to open it and you'll quickly understand how it works. + +Now, to get the file onto our Raspberry PI we need to download it from the webserver. +One way would be to use the `wget` program to do so. +We know *where* the server is by it's IP address, plus we also know the *filename*. +Putting these two together we can construct the following line. + +```bash +wget 172.30.6.96/accounts.csv +``` + +This will download the file to the directory we're in and will save it as `accounts.csv`. +You can change the output filename it you want, just have a look at the `wget` options via `wget --help` or our trusty `man wget`. + +## Extracting the data we need + +A quick `cat accounts.csv` gives us the following output: + +```bash +EMAIL,LASTNAME,FIRSTNAME,MATRIX,GITEA,TEAM +1h.lust.hugo@gmail.com,Lust,Hugo,@hugo_lust:86thumbs.net,https://gitea.86thumbs.net/Hugo,red +ticus@kraland.net,krstev,vladimir,@vl4dd:86thumbs.net,https://gitea.86thumbs.net/vl4dd,blue +adamd@outlook.be,Adam,David,@adamd73:matrix.org,https://gitea.86thumbs.net/adamd,red +nicohawai@gmail.com,Perez,Nicolas,@hawai:86thumbs.net,https://gitea.86thumbs.net/Hawai,blue +nicolas.wattripont@gmail.com,Wattripont,Nicolas,@wawa142:86thumbs.net,https://gitea.86thumbs.net/wawa142,red +laurentdelvigne@hotmail.com,Delvigne,Laurent,@ldelvigne:86thumbs.net,https://gitea.86thumbs.net/ldelvigne,blue +sselcukaslan@gmail.com,Aslan,Selçuk,@slck:86thumbs.net,https://gitea.86thumbs.net/selcuk,blue +Sarah24886@hotmail.com,Rmiki,Sarah,@sarahrm95:matrix.org,https://gitea.86thumbs.net/sarahrm95,blue +knoppixs@hotmail.com,Abbamoulay,Abdellah,@knoppixs:86thumbs.net,https://gitea.86thumbs.net/Abdellah,red +JonathanDechief@hotmail.com,Dechief,Jonathan,@elewene:matrix.org,https://gitea.86thumbs.net/Elewene,red +51207@etu.he2b.be,,Aliou,@aliou:86thumbs.net,https://gitea.86thumbs.net/aliou,blue +``` + +### The $USERNAME + +To extract the `$USERNAME` we're interested in the fourth collumn which has the MATRIX login handle. +We can extract only this collumn by using `cut` with `,` as a delimiter. + +```bash +cat accounts.csv | cut -d "," -f 4 +``` + +This leaves us with only the MATRIX login handles which is a good start but there is still a bit too much information . +We need to drop the first line, which is the *header* of the CSV file, plus crop between the `@` and the `:`. +These two operations can be done is multiple ways but I suggest this modification. +It is not the most elegant solution but it uses only tools you have used this far. +The `tail` command drops the *header* line, and the two `cut` commands trim the username to just what we need. + +```bash +cat accounts.csv | cut -d "," -f 4 | tail -n +2 | cut -d ":" -f 1 | cut -d "@" -f 2 +``` + +Done! +We have all the usernames we need. +We can save this to a file by redirecting the STDOUT to a file with the following command. + +```bash +cat accounts.csv | cut -d "," -f 4 | tail -n +2 | cut -d ":" -f 1 | cut -d "@" -f 2 > usernames.list +``` + +### The $PASSWORD + +To extract the password we need to combine two field from the CSV file. +A *really* good command line program to accieve this is `awk`. +Don't forget the man pages! + +```bash +cat accounts.csv | awk -F "," '{print $2 $3}' | tail -n +2 +``` + +If you feel like making the password complexer, you can try to add in extra data into the `awk` command, or even append random numbers to the end. + +```bash +cat accounts.csv | awk -F "," '{print $2 "_helloworld_" $3}' | tail -n +2 +``` + +We can now save these passwords to a file in the same way as before. + +### The $GROUP + +This is an *easy* one because it requires no real modification of the field. + +```bash +cat accounts.csv | tail -n +2 | cut -d "," -f 6 > groups.list +``` + +## Using this information to create accounts + +We now have command that extracts the information we need, plus three separate files that contain all the information. +This is a good moment to try and write a very simple script. +I'll first try to do it without a loop but you'll quickly see it's a *lot* easier with a loop in there. +Remember that `$1` represents the first argument on the command line so that when calling our script with `./script.sh 3` we'll get the username, password and group for the third user. +A combination of `head | tail` is a [classic](https://stackoverflow.com/questions/6022384/bash-tool-to-get-nth-line-from-a-file) way of selection only one file from a file. +Last but not least, don't forget to add execution permissions to this script with `chmod`. + +```bash +#!/bin/bash + +LINE=$1 + +head -$1 usernames.list | tail -1 +head -$1 passwords.list | tail -1 +head -$1 groups.list | tail -1 +``` + +We can then *copy/paste* this information to create the following line. +We'll be prompted to paste in the proper information. + +```bash +sudo adduser $USERNAME +``` + +Needless to say this is a labour intensive operation that we can automate with a mini script. + +### Putting it together as a script + +Brace yourselves a bit but I promise it's worth it! +The only thing we have not seen is how to save the output of a command into a variable. +This can be done with the `$(...)` syntax. +I know it looks a bit cryptic but an example speaks more than words. + +```bash +NOW=$(date) +echo $NOW +``` + +With this in mind, the following code should make sense. +We're doing the exact same thing but saving the output of each command into a variable. +At the last line we *use* the variables to create a message. + +```bash +#!/bin/bash + +LINE=$1 + +USERNAME=$(head -$1 usernames.list | tail -1) +PASSWORD=$(head -$1 passwords.list | tail -1) +GROUP=$(head -$1 groups.list | tail -1) + +echo "user: $USERNAME password: $PASSWORD group: $GROUP" +``` + +This just output's all information onto one line, but why not *use* this information to actually create the accounts? +A counterpart to the `adduser` program you're used to using, there is also `useradd` which is better suited for scripting purposes. +By default `useradd` is very *barebones* and does not create a home directory for the user but a quick look at the `man useradd` pages tells us we can use the `-m` flag to do so. +This tells us the the command `useradd $USERNAME -m` will create a user for us with his/her own home directory. +A [google search](https://linux.die.net/man/8/chpasswd) pointed me to `chpasswd` to set passwords from within a script. +The line to set the password will be `echo $USERNAME:$PASSWORD | chpasswd`. +This gives us the following script. + +```bash +#!/bin/bash + +LINE=$1 + +USERNAME=$(head -$1 usernames.list | tail -1) +PASSWORD=$(head -$1 passwords.list | tail -1) +GROUP=$(head -$1 groups.list | tail -1) + +echo "adding user: $USERNAME" +useradd $USERNAME -m + +echo "setting password: $PASSWORD for $USERNAME" +echo $USERNAME:$PASSWORD | chpasswd +``` + +You probably noticed I did not add the users to their *red/blue* groups. +We can add them on the `useradd` line with the `-G` flag but it would fail if the group does not exist yet. +The `groupadd` command will add a group to the system and if we add the `-f` flag to it will do so without complaining if the group already exists. +This way we can just execute that line each time without worrying wether the group exists or not. + +```bash +#!/bin/bash + +LINE=$1 + +USERNAME=$(head -$1 usernames.list | tail -1) +PASSWORD=$(head -$1 passwords.list | tail -1) +GROUP=$(head -$1 groups.list | tail -1) + +echo "making sure $GROUP exists..." +groupadd -f $GROUP + +echo "adding user: $USERNAME" +useradd $USERNAME -m -G $GROUP + +echo "setting password: $PASSWORD for $USERNAME" +echo $USERNAME:$PASSWORD | chpasswd +``` + +Those who switched to the newly created user noticed that the shell is *very* basic one. +You can find out which shell these new accounts use by looking at the `/etc/passwd` file. +There are multiple ways to sort this problem but a look at the `man useradd` pages tells us we can use the `-s` flag to set the shell we want for the user. +We probably want to use `/bin/bash` for this option! + +```bash +#!/bin/bash + +LINE=$1 + +USERNAME=$(head -$1 usernames.list | tail -1) +PASSWORD=$(head -$1 passwords.list | tail -1) +GROUP=$(head -$1 groups.list | tail -1) + +echo "making sure $GROUP exists..." +groupadd -f $GROUP + +echo "adding user: $USERNAME" +useradd $USERNAME -m -G $GROUP -s "/bin/bash" + +echo "setting password: $PASSWORD for $USERNAME" +echo $USERNAME:$PASSWORD | chpasswd + +echo "adding $USERNAME to $GROUP" +``` + +This is getting pretty close to perfect! +We can now run through all of the lines of the file one by one and automatically create the proper user, password and group combinations. +To know how many accounts we have to create we can use `wc -l accounts.csv` and then just run the script, incrementing the number each time. + +```bash +sudo ./script.sh 1 +sudo ./script.sh 2 +sudo ./script.sh 3 +echo "etc..." +``` + +### Taking it further as an extra challenge + +If we want to automate the entire thing we'll need a loop to *loop through* every line in the `accounts.csv` file. +Bash loops are for a further class but I'll leave you with this quick example for those who feel like messing around. +Remember the *oneliners* we constructed at the beginning to extract the relevant information from the line! +Don't worry if this looks to complicated at the moment, we'll do this exersise again when we're looking into [bash scripting](https://ryanstutorials.net/bash-scripting-tutorial/). + +```bash +#!/bin/bash + +FILE=$1 +LINES=$(cat $1) + +for LINE in $LINES; +do + echo $LINE +done +``` + +## Setting up the fileserver + +### FTP + +A quick [google](https://likegeeks.com/ftp-server-linux/) tells us `vsftpd` is a popular *FileTransferProtocol* server. +As expected you can find it in the main Debian repositories. +You know how to install it by now! + +```bash +sudo apt search vsftpd +``` + +To know *where* to configure the server we can look at the `man vsftpd` pages. +Scroll all the way to the bottom to see which files it uses to configure itself. +The configuration file itself is very *verbose* and should explain itself. + +### SFTP + +TODO