qemush/README.md

# `qemush` - A suckless QEMU wrapper written in shell

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## How does it work

`qemush` allows to run commands as Unix user `qemu` to manage virtual
machines and their disks associated.

## Why

`qemush` is **daemonless**: no bloaty long running process is needed for
`qemush` to work.

`qemush` is **lightweight**: it only consists in a shell script to
automate repeated tasks and force good practices.

`qemush` needs **few dependencies**: see section
[Dependencies](#dependencies) for details.

`qemush` is **hackable**: you can [write your own launching
scripts](#writing-a-launching-script) to make it work as intended.

`qemush` is **easy to setup**: you can make it work in a few steps, see
section [Installation instructions](#installation-instructions).

## Good practices?

Here is a list of good practices forced by `qemush`.

- **Processes running as user `qemu`**: members of group `qemu` can manage
the same virtual machines
- **Modularization**: `qemush` launching scripts are intended to be
stackable to reuse common `qemu` parameters in all virtual machines
needing them
keep track of them
- **Copy-on-write**: images are formatted using `qcow2` to use less space
on disk
- **Process detachment**: you can log out and have your virtual machines
still running, control them via Unix sockets

## Is it better than `libvirt` ?

No. `qemush` and `libvirt` are for different use cases. `qemush` will allow you to spin up virtual machines really fast and with as little setup as possible, and aims to be nothing more than a QEMU wrapper, while `libvirt` will offer better out-of-the-box experience, with already existing pre-configurations, associated tools like the `virt-manager` GUI and a friendlier process supervision. You should use `qemush` if you care about controlling every aspect of your virtual machines, and are already used to using bare QEMU without an abstraction layer.

## Dependencies

From version 0.9.0, `qemush` is written in pure POSIX shell! The previous dependency on `bash` was removed in consequence.

All dependencies are common packages for a distribution, you'll be able to
grab them from your favorite packages sources.

- `qemu` - this is literally a QEMU wrapper so there's a chance you'll
need it
- A POSIX compliant shell - `bash` (POSIX mode), `*ash`, `*ksh` are POSIX shells
- `coreutils` - used for basic OS operations
- `sudo` - execute commands as `qemu`
- `socat` - monitor machines via Unix sockets
- any text editor - used for builtin function to edit launching scripts

## Installation instructions

### QEMU user and group

`qemush` acts as Unix user `qemu` to manage virtual machines. You need to
create a system user `qemu` that cannot login, with any home directory,
in an Unix group of the same name. Example:

```sh
# Example if the qemu user doesn't exist
# Make sure /etc/shells contains /bin/nologin
useradd -r -s /bin/nologin qemu
```

For ease of use, you need to grant every user in the `qemu` group via
`sudo` the right to execute commands as `qemu`. You can find an example
`sudoers` rule in this repo's `etc/sudoers.d` folder.

### Via `Makefile` (recommended)

Just run the following command at the root of this repository to install
`qemush` (previous step is **mandatory**) :

```sh
make
```

> And what if I don't want to bindly run this obscure `Makefile` ???

You'd be right. The next section is the exhaustive list of steps handled
by the `Makefile` for the installation process.

### Manual installation (what does the `Makefile` do)

- Create `disks`, `launchers` and `bin` directories in `~qemu`
- Copy `qemush` scripts parts from `qemu/bin` in `~qemu/bin` with mode
`740`
- Compile C programs from `src` in `~qemu/bin` with mode `740`
- Copy the default launching scripts to `~qemu/launchers` with mode `740`
- Copy `bin/qemush` to `/usr/local/bin/qemush` with mode `755`

## Usage

### Writing a launching script

The default text editor used by `qemush` is `nvim`, but it can be
overriden by the `EDITOR` environment variable.

Run the following command to start editing a launching script by the name
of your choice:

```sh
qemush edit "$name"
```

Example scripts are available in this repo's `qemu/launchers` folder.

### Launching a virtual machine

Virtual machines are identified by the name of their launching scripts.
You can launch any machine with the following command:

```sh
qemush start "$name"
```

You can also list all available virtual machines by running this command:

```sh
qemush ls
```

### Other uses

You can show the full list of possible actions by running this command:

```sh
qemush help
```