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# Building and installing letmein
## Prerequisites
The Rust compiler must be installed to build letmein.
It is recommended to use the latest version of the stable Rust compiler:
[Rust installer](https://www.rust-lang.org/tools/install)
The Rust installer will install the compiler and the build tool `cargo`.
The build requires the additional `cargo-audit` and `cargo-auditable` tools to be installed.
Run this command to install both tools:
```sh
cargo install cargo-audit cargo-auditable
```
At runtime the nftables `nft` binary is required to be installed reachable in the `$PATH`.
On Debian please install the `nftables` package:
```sh
apt install nftables
```
## Building letmein
Run the `build.sh` script to build letmein.
After installing all build prerequisites, run the build script:
```sh
./build.sh
```
## Installing letmein
### Install client
Then run the `install-client.sh` to install the letmein client to `/opt/letmein/`:
```sh
./install-client.sh
```
The client is used to send a knock packet to the server.
### Install server
#### Prepare user and group for the server
The public network facing part of the letmein server runs with reduced privileges to reduce the attack surface.
For this to work, the user `letmeind` and the group `letmeind` have to be present in `/etc/passwd` and `/etc/group`.
It is recommended for this user to not have a shell and home assigned and therefore not be a login-user.
You can use the following helper script to create the user and group in your system:
```sh
./create-user.sh
```
#### Install the server and systemd units
After building and creating the `letmeind` system user, run the `install-server.sh` to install the letmeind server to `/opt/letmein/`:
```sh
./install-server.sh
```
Installing the server will also install the service and socket into systemd and start the letmeind server.
The server is used to receive knock packets from the client.
Upon successful knock authentication, the server will open the knocked port in its `nftables` firewall.
## Installing with `cargo install` from crates.io
Alternatively, you can install letmein, letmeind and letmeinfwd with `cargo install` from [crates.io](https://crates.io/).
Note that there are a few important differences when using `cargo install` instead of the `install*.sh` scripts from above:
- letmein will look for configuration files in `/etc` instead of `/opt/letmein/etc`.
- The system user and group `letmeind` will not be installed in the operating system. The user and group are required for server operation.
- The systemd sockets and services will not be installed in the operating system.
You may use `cargo install` to install the `letmein` client application.
But it is *not* recommended to use `cargo install` to install the `letmeind` and `letmeinfwd` server daemons.
## Arch Linux: Installing from AUR
If you use [Arch Linux](https://archlinux.org/), then you can install the client and the server from [AUR](https://aur.archlinux.org/packages/letmein).
The AUR package will install the configuration to `/etc` and the binaries to `/usr/bin`.
(The AUR package is maintained by a third party maintainer. Thanks!)
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