diff --git a/.gitignore b/.gitignore
index ea8c4bf..c35a4ed 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 /target
+/work
diff --git a/Cargo.lock b/Cargo.lock
index b62e2bd..0ea7ce1 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1023,6 +1023,15 @@ dependencies = [
  "lazy_static",
 ]
 
+[[package]]
+name = "signal-hook-registry"
+version = "1.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9203b8055f63a2a00e2f593bb0510367fe707d7ff1e5c872de2f537b339e5410"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "slab"
 version = "0.4.11"
@@ -1149,6 +1158,7 @@ dependencies = [
  "libc",
  "mio",
  "pin-project-lite",
+ "signal-hook-registry",
  "socket2 0.6.1",
  "tokio-macros",
  "windows-sys 0.61.2",
diff --git a/Cargo.toml b/Cargo.toml
index 234ebc4..b3ff8a3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,7 +14,7 @@ opentelemetry-otlp = { version = "0.13.0", optional = true }
 opentelemetry-semantic-conventions = { version = "0.12.0", optional = true }
 serde = { version = "1.0.228", default-features = false, features = ["std", "derive"] }
 serde_json = { version = "1.0.149", default-features = false, features = ["std"] }
-tokio = { version = "1.49.0", default-features = false, features = ["rt", "rt-multi-thread", "fs", "io-util"] }
+tokio = { version = "1.49.0", default-features = false, features = ["rt", "rt-multi-thread", "fs", "io-util", "process"] }
 toml = { version = "0.9.11", default-features = false, features = ["display", "parse", "serde", "std"] }
 tracing = { version = "0.1.37", optional = true }
 tracing-opentelemetry = { version = "0.20.0", optional = true }
diff --git a/example_config.toml b/example_config.toml
index 2e35173..e752a45 100644
--- a/example_config.toml
+++ b/example_config.toml
@@ -1,17 +1,17 @@
-work_directory = "/home/nixworker/persist/nix_builder"
+# work_directory = "/home/nixworker/persist/nix_builder"
 
 [[targets]]
-name = "odo"
-repo = "https://code.fizz.buzz/talexander/machine_setup.git"
-branch = "nix"
-path = "nix/configuration"
-attr = "odo"
+  name = "odo"
+  repo = "https://code.fizz.buzz/talexander/machine_setup.git"
+  branch = "nix"
+  path = "nix/configuration"
+  attr = "odo"
 
 [[targets]]
-name = "odo_update"
-repo = "https://code.fizz.buzz/talexander/machine_setup.git"
-branch = "nix"
-path = "nix/configuration"
-attr = "odo"
-update = true
-update_branch = "nix_update"
+  name = "odo_update"
+  repo = "https://code.fizz.buzz/talexander/machine_setup.git"
+  branch = "nix"
+  path = "nix/configuration"
+  attr = "odo"
+  update = true
+  update_branch = "nix_update"
diff --git a/src/command/build/runner.rs b/src/command/build/runner.rs
index b14d18f..702651a 100644
--- a/src/command/build/runner.rs
+++ b/src/command/build/runner.rs
@@ -2,6 +2,10 @@ use crate::cli::parameters::BuildArgs;
 use crate::config::Config;
 use crate::config::TargetConfig;
 use crate::error::CustomError;
+use crate::fs_util::assert_directory;
+use crate::fs_util::is_git_repo;
+use crate::git_util::git_force_into_state;
+use crate::git_util::git_init_at_rev;
 
 pub(crate) async fn run_build(args: BuildArgs) -> Result<(), CustomError> {
     println!("{:?}", args);
@@ -18,12 +22,41 @@ pub(crate) async fn run_build(args: BuildArgs) -> Result<(), CustomError> {
             }
         };
 
-        prepare_flake_repo(target_config).await?;
+        prepare_flake_repo(&config, target_config).await?;
     }
 
     Ok(())
 }
 
-async fn prepare_flake_repo(target_config: &TargetConfig) -> Result<(), CustomError> {
-    todo!()
+async fn prepare_flake_repo(
+    config_root: &Config,
+    target_config: &TargetConfig,
+) -> Result<(), CustomError> {
+    let flake_directory = target_config.get_flake_directory(config_root)?;
+    assert_directory!(
+        &flake_directory,
+        "Creating flake directory {}",
+        (&flake_directory).to_string_lossy()
+    );
+
+    if is_git_repo(&flake_directory).await? {
+        // Clean up the existing clone
+        git_force_into_state(
+            &flake_directory,
+            target_config.get_branch()?,
+            "origin",
+            target_config.get_repo()?,
+            target_config.get_revision()?,
+        )
+        .await?;
+    } else {
+        git_init_at_rev(
+            &flake_directory,
+            target_config.get_branch()?,
+            target_config.get_repo()?,
+            target_config.get_revision()?,
+        )
+        .await?;
+    }
+    Ok(())
 }
diff --git a/src/config/target.rs b/src/config/target.rs
index 57c0cba..07c4ffa 100644
--- a/src/config/target.rs
+++ b/src/config/target.rs
@@ -12,16 +12,23 @@ use super::Config;
 pub(crate) struct TargetConfig {
     pub(super) name: String,
 
-    #[serde(default)]
-    pub(super) repo: Option<String>,
+    pub(super) repo: String,
+
     #[serde(default)]
     pub(super) branch: Option<String>,
+
+    #[serde(default)]
+    pub(super) revision: Option<String>,
+
     #[serde(default)]
     pub(super) path: Option<String>,
+
     #[serde(default)]
     pub(super) attr: Option<String>,
+
     #[serde(default)]
     pub(super) update: Option<bool>,
+
     #[serde(default)]
     pub(super) update_branch: Option<String>,
 }
@@ -42,4 +49,20 @@ impl TargetConfig {
         let target_directory = self.get_target_directory(config_root)?;
         Ok(Cow::Owned(target_directory.join("flake")))
     }
+
+    pub(crate) fn get_repo(&'_ self) -> Result<&String, CustomError> {
+        Ok(&self.repo)
+    }
+
+    pub(crate) fn get_branch(&'_ self) -> Result<Cow<'_, str>, CustomError> {
+        if let Some(b) = &self.branch {
+            Ok(Cow::Borrowed(b))
+        } else {
+            Ok(Cow::Borrowed("main"))
+        }
+    }
+
+    pub(crate) fn get_revision(&self) -> Result<&Option<String>, CustomError> {
+        Ok(&self.revision)
+    }
 }
diff --git a/src/fs_util.rs b/src/fs_util.rs
new file mode 100644
index 0000000..013fe4f
--- /dev/null
+++ b/src/fs_util.rs
@@ -0,0 +1,36 @@
+macro_rules! assert_directory {
+    ($dir:expr, $($params:tt)*) => {{
+        let dir = $dir;
+        let metadata = tokio::fs::metadata(&dir).await;
+        match metadata {
+            Ok(metadata) if !metadata.is_dir() => {
+                tracing::info!($($params)*);
+                tokio::fs::create_dir_all(dir).await?;
+            }
+            Err(_) => {
+                tracing::info!($($params)*);
+                tokio::fs::create_dir_all(dir).await?;
+            }
+            Ok(_) => {}
+        };
+    }};
+}
+use std::path::Path;
+
+pub(crate) use assert_directory;
+
+use crate::error::CustomError;
+
+pub(crate) async fn is_directory<D: AsRef<Path>>(dir: D) -> Result<bool, CustomError> {
+    let metadata = tokio::fs::metadata(dir).await;
+    let result = match metadata {
+        Ok(metadata) if metadata.is_dir() => true,
+        _ => false,
+    };
+    Ok(result)
+}
+
+pub(crate) async fn is_git_repo<D: AsRef<Path>>(dir: D) -> Result<bool, CustomError> {
+    let dot_git = dir.as_ref().join(".git");
+    is_directory(dot_git).await
+}
diff --git a/src/git_util/core.rs b/src/git_util/core.rs
new file mode 100644
index 0000000..127bac3
--- /dev/null
+++ b/src/git_util/core.rs
@@ -0,0 +1,236 @@
+use tokio::process::Command;
+
+use crate::error::CustomError;
+use std::ffi::OsStr;
+use std::path::Path;
+
+pub(crate) async fn git_init<P, B>(dest: P, branch: B) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    B: AsRef<str>,
+{
+    // git -C $dest init --initial-branch=$branch
+
+    let mut command = Command::new("git");
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["init"]);
+    command.arg(format!("--initial-branch={}", branch.as_ref()));
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to init git repository: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    Ok(())
+}
+
+pub(crate) async fn git_remote_add<P, N, U>(dest: P, name: N, url: U) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    N: AsRef<str>,
+    U: AsRef<str>,
+{
+    // git -C $dest remote add $name $url
+
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    let name = name.as_ref();
+    let url = url.as_ref();
+    let mut command = Command::new("git");
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["remote", "add"]);
+    command.arg(name);
+    command.arg(url);
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to add remote to git repo: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    Ok(())
+}
+
+pub(crate) async fn git_fetch<P, N, R>(
+    dest: P,
+    name: N,
+    rev: R,
+    depth: Option<usize>,
+    blobless: bool,
+    treeless: bool,
+) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    N: AsRef<str>,
+    R: AsRef<str>,
+{
+    // git -C $dest fetch [--depth=$depth] [--filter=blob:none] [--filter=tree:0] $name $rev
+
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    let name = name.as_ref();
+    let mut command = Command::new("git");
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["fetch"]);
+    if let Some(d) = depth {
+        command.arg(format!("--depth={}", d));
+    }
+    if blobless {
+        command.arg("--filter=blob:none");
+    }
+    if treeless {
+        command.arg("--filter=tree:0");
+    }
+    command.arg(name);
+    command.arg(rev.as_ref());
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to git fetch: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    Ok(())
+}
+
+pub(crate) async fn git_checkout<P, R>(
+    dest: P,
+    rev: R,
+    force: bool,
+    detach: bool,
+) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    R: AsRef<str>,
+{
+    // git -C $dest checkout [--force] [--detach] $rev
+
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    let mut command = Command::new("git");
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["checkout"]);
+    if force {
+        command.arg("--force");
+    }
+    if detach {
+        command.arg("--detach");
+    }
+    command.arg(rev.as_ref());
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to git checkout: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    Ok(())
+}
+
+pub(crate) async fn git_get_remote<P, R>(dest: P, remote: R) -> Result<String, CustomError>
+where
+    P: AsRef<Path>,
+    R: AsRef<str>,
+{
+    // git -C $dest remote get-url $remote
+
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    let mut command = Command::new("git");
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["remote", "get-url"]);
+    command.arg(remote.as_ref());
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to get git remote: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    let url = {
+        let mut url = String::from_utf8(output.stdout)?;
+        url.truncate(url.trim_ascii_end().len());
+        url
+    };
+    Ok(url)
+}
+
+#[allow(dead_code)]
+pub(crate) async fn git_reset<P, R>(dest: P, hard: bool, rev: R) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    R: AsRef<str>,
+{
+    // git -C $dest reset [--hard] $rev
+
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    let rev = rev.as_ref();
+    let mut command = Command::new("git");
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["reset"]);
+    if hard {
+        command.arg("--hard");
+    }
+    command.arg(rev);
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to git reset: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    Ok(())
+}
+
+pub(crate) async fn git_clean<P>(
+    dest: P,
+    recurse_into_untracked_directories: bool, // -d
+    force: bool,                              // -f
+    dont_use_ignore_rules: bool,              // -x
+) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+{
+    // git -C $dest clean [-dfx]
+
+    let dest = AsRef::<OsStr>::as_ref(dest.as_ref());
+    let mut command = Command::new("git");
+    command.arg("-C");
+    command.arg(dest);
+    command.args(&["clean"]);
+    if recurse_into_untracked_directories {
+        command.arg("-d");
+    }
+    if force {
+        command.arg("--force");
+    }
+    if dont_use_ignore_rules {
+        command.arg("-x");
+    }
+    command.kill_on_drop(true);
+    let output = command.output().await?;
+    if !output.status.success() {
+        return Err(format!(
+            "Failing to git clean: {}",
+            String::from_utf8(output.stderr)?
+        )
+        .into());
+    }
+    Ok(())
+}
diff --git a/src/git_util/high_level.rs b/src/git_util/high_level.rs
new file mode 100644
index 0000000..0048782
--- /dev/null
+++ b/src/git_util/high_level.rs
@@ -0,0 +1,85 @@
+use crate::error::CustomError;
+use crate::fs_util::assert_directory;
+use crate::git_util::git_checkout;
+use crate::git_util::git_clean;
+use crate::git_util::git_fetch;
+use crate::git_util::git_get_remote;
+use crate::git_util::git_init;
+use crate::git_util::git_remote_add;
+use std::path::Path;
+
+pub(crate) async fn git_init_at_rev<P, B, U>(
+    dest: P,
+    branch: B,
+    url: U,
+    rev: &Option<String>,
+) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    B: AsRef<str>,
+    U: AsRef<str>,
+{
+    // mkdir -p $dest
+    // git -C $dest init --initial-branch=main
+    // git -C $dest remote add origin $url
+    // git -C $dest fetch --depth 1 origin ($rev|$branch)
+    // git -C $dest checkout FETCH_HEAD
+
+    assert_directory!(&dest, "Cloning git repo into {}", dest.as_ref().display());
+
+    let fetch_target = rev.as_deref().unwrap_or(branch.as_ref());
+
+    git_init(&dest, "main").await?;
+    git_remote_add(&dest, "origin", url).await?;
+    git_fetch(&dest, "origin", fetch_target, Some(1), false, false).await?;
+    git_checkout(&dest, "FETCH_HEAD", false, false).await?;
+
+    Ok(())
+}
+
+pub(crate) async fn git_force_into_state<P, B, R, U>(
+    dest: P,
+    branch: B,
+    remote: R,
+    url: U,
+    rev: &Option<String>,
+) -> Result<(), CustomError>
+where
+    P: AsRef<Path>,
+    B: AsRef<str>,
+    R: AsRef<str>,
+    U: AsRef<str>,
+{
+    // Maybe instead
+    // git -C $dest fetch --depth 1 $remote ($rev|$branch)
+    // git -C $dest checkout --detach --force FETCH_HEAD
+    // git -C $dest clean -dfx
+
+    let fetch_target = rev.as_deref().unwrap_or(branch.as_ref());
+
+    check_remote_correct(&dest, &remote, url).await?;
+    git_fetch(&dest, &remote, fetch_target, Some(1), false, false).await?;
+    git_checkout(&dest, "FETCH_HEAD", true, true).await?;
+    git_clean(&dest, true, true, true).await?;
+
+    Ok(())
+}
+
+async fn check_remote_correct<F, R, U>(folder: F, remote: R, url: U) -> Result<(), CustomError>
+where
+    F: AsRef<Path>,
+    R: AsRef<str>,
+    U: AsRef<str>,
+{
+    let existing_remote = git_get_remote(folder, &remote).await?;
+    if existing_remote != url.as_ref() {
+        return Err(format!(
+            "Existing remote {} does not have the expected URL {} != {}",
+            remote.as_ref(),
+            existing_remote,
+            url.as_ref()
+        )
+        .into());
+    }
+    Ok(())
+}
diff --git a/src/git_util/mod.rs b/src/git_util/mod.rs
new file mode 100644
index 0000000..8227dd4
--- /dev/null
+++ b/src/git_util/mod.rs
@@ -0,0 +1,4 @@
+mod core;
+mod high_level;
+pub(crate) use core::*;
+pub(crate) use high_level::*;
diff --git a/src/main.rs b/src/main.rs
index 7a508f2..4ea65eb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -13,6 +13,8 @@ mod cli;
 mod command;
 mod config;
 mod error;
+mod fs_util;
+mod git_util;
 mod init_tracing;
 
 fn main() -> Result<ExitCode, CustomError> {