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:
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.
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/).
Even without installing any additional server, we can offer our users a way to download, and upload, files to our server.
When you install `openssh-server`, and pay attention to the installation dialog, you'll see it will also install an additional package called `openssh-sftp-server`
This in itself is enough to have an SFTP server up and running.
Done!
It does raise the question of security.
When installing the `vsftpd` package your users can *only* upload and download files but when you install an ssh server they can also get shell access!
This might not be the desired behaviour for all your users.
Luckily we can change the server configuration to modify it to our requirements.
How will we find *which* configuration file we need to change *where*?
`man sshd` should do the trick.
Navigate to to end of the manual and you'll see a huge list of files the server uses to configure itself.
Why `sshd` and not `ssh` you ask?
Well, `ssh` is the **client** you use to connect to the `sshd`**server** and thet are to different *programs*.
Remember that `ssh` was installed on your Linux machine even before installing `openssh-server`!
I can think of two ways to limit the shell access for specific users.
The first one should ring a bell.
As we define our default shell in the `/etc/passwd` file to be `/bin/bash`, we can also change this for specific users to `/usr/sbin/nologin`.
This will block those users from getting an actual shell when sshing into the machine but SFTP should still work.
There are multiple downsides to this solution, some of which we'll investigate further later one, but the main one I see from a beginner point of view is that it requires a customisation for each account we want to block.
As all users we want to block are part of a group, either *red* or *blue* there should be a way to restrict access on a group based level no?
It's the last lines of the configuration file that point out some interesting features.
```bash
# override default of no subsystems
Subsystem sftp /usr/lib/openssh/sftp-server
# Example of overriding settings on a per-user basis
#Match User anoncvs
# X11Forwarding no
# AllowTcpForwarding no
# PermitTTY no
# ForceCommand cvs server
```
Remember that the `#` are comments.
These settings point out that we can add different rules for different users, and probably groups as well.
So, if you trust all people in the *blue* group, you can add a rule to match all users in the *red* group and restrict them to only sftp login and no shell access.
With this in mind, what would adding the following to the configuration file do?
```bash
Match Group blue
ForceCommand internal-sftp
```
But the users can still walk around the entire file system, which is not always a good idea.
Using the keywords **sftp**, **chroot**, **group** in [google](https://googlethatforyou.com?q=sftp%20chroot%20group) lists us the [arch](https://wiki.archlinux.org/index.php/SFTP_chroot) wiki which is *always* a solid place to inform ourselves.
Try to have get this set up as an additional exersise!
### Taking changes to configuration files into account
When make these changes to the configuration files you probably noticed they are not applied immidiatly.
So when are they taken into account then?
Most servers we'll install onto our various machines run as [daemons](https://en.wikipedia.org/wiki/Daemon_(computing)) in the background.
They listen on for an incoming client connection on a port, do whatever the client requests of them and go back to sleep when there are no tasks for them to perform.
They might have internal tasks scheduled but we'll set this aside for the moment.
As with most things Linux, configuration is done by a text file and *most* daemons will read their corresponding configuration files upon startup.
Think of the .bashrc file, which is read every time a new shell is started.
Once they know how to behave, from reading their configuration file, they will act accordingly.
This raises the question, how do you *restart* a running server?
The system responsible for launching most daemons on our Debian installions, and also our Raspberry PI's, is called **systemd**.
The thee most used commands you need to know are as follows.
How do to *start* a service, how to *stop* one and how to *check* if one is running properly.
For system daemons, such as `sshd` or most webservers, you need administrator powers to interact with them.
```bash
sudo systemctl start sshd.service
sudo systemctl stop sshd.service
sudo systemctl status sshd.service
```
These three commands will go a long way but there are other handy ones you can try out.
I advise you to use *tab-completion* as much as possible as it will help you to construct the proper commands.
Especially at the beginning of your Linux journey because it takes some time to rememeber specific service names.
Have a look at all the base commands of `systemctl` and you'll notice quite a few interesting things.
For example, it can be used to reboot or shutdown your computer as well!
For those who want to digg deeper into systemd itself I advise you to have a browse in it's configuration directory.
You'll find it at `/etc/systemd` and the manpages `man systemd` are also very helpfull, but a bit verbose.
We will have a deeper look at the internals of systemd later throughout the course.
