Rewrite init script in rust and fix non-shell CMDs

Cargo.lock

@@ -66,15 +66,15 @@ checksum = "330a5ed07fa54e4702c9d6c4174f74427fc0ef6e214bbd677ae50a5099946470"
 
 [[package]]
 name = "base64"
-version = "0.22.1"
+version = "0.23.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
+checksum = "ac07cdecf99051d9a5238b80f35af32cdeba5b336e55d957b318b50137e18da5"
 
 [[package]]
 name = "bitflags"
-version = "2.13.1"
+version = "2.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b588b76d00fde79687d7646a9b5bdf3cc0f655e0bbd080335a95d7e96f3587da"
+checksum = "3ded4057c258ba199e2d26386d3af3780957ecaee6c4ef4041c6b4b8b97c0b06"
 
 [[package]]
 name = "cfg-if"
@@ -82,6 +82,12 @@ version = "1.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f079e83a288787bcd14a6aea84cee5c87a67c5a3e660c30f557a3d24761b3527"
+
 [[package]]
 name = "clap"
 version = "4.6.6"
@@ -155,12 +161,13 @@ checksum = "da7c62ceae207dd37ea5b845da6a0696c799f85e97da1ab5b7910be3c1c80223"
 
 [[package]]
 name = "flate2"
-version = "1.1.9"
+version = "1.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "843fba2746e448b37e26a819579957415c8cef339bf08564fe8b7ddbd959573c"
+checksum = "6e634e2e0ebac1ee034020da1ca582e17ffe4e0f5e985823721e168928136dcb"
 dependencies = [
  "crc32fast",
  "miniz_oxide",
+ "zlib-rs",
 ]
 
 [[package]]
@@ -212,14 +219,26 @@ checksum = "cf8baf1c55e62ffcace7a9f06f4bd9cd3f0c4beb022d3b367256b91b87513d98"
 
 [[package]]
 name = "miniz_oxide"
-version = "0.8.9"
+version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1fa76a2c86f704bdb222d66965fb3d63269ce38518b83cb0575fca855ebb6316"
+checksum = "b63fbc4a50860e98e7b2aa7804ded1db5cbc3aff9193adaff57a6931bf7c4b4c"
 dependencies = [
  "adler2",
  "simd-adler32",
 ]
 
+[[package]]
+name = "nix"
+version = "0.31.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cf20d2fde8ff38632c426f1165ed7436270b44f199fc55284c38276f9db47c3d"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "cfg_aliases",
+ "libc",
+]
+
 [[package]]
 name = "once_cell"
 version = "1.21.4"
@@ -332,6 +351,14 @@ dependencies = [
  "xdg",
 ]
 
+[[package]]
+name = "slim-init"
+version = "0.1.0"
+dependencies = [
+ "base64",
+ "nix",
+]
+
 [[package]]
 name = "strsim"
 version = "0.11.1"
@@ -340,9 +367,9 @@ checksum = "7da8b5736845d9f2fcb837ea5d9e2628564b3b043a70948a3f0b778838c5fb4f"
 
 [[package]]
 name = "syn"
-version = "3.0.4"
+version = "3.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e6275cddf4610d1775e6d1fe9469b2e77d0f39fd98fb7450901b821e0c53649f"
+checksum = "12df2e0110f65b775f769bb17ef989067a1d931b2eb822bd4346631eeada89f9"
 dependencies = [
  "proc-macro2",
  "quote",
@@ -395,6 +422,12 @@ version = "3.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2fb433233f2df9344722454bc7e96465c9d03bff9d77c248f9e7523fe79585b5"
 
+[[package]]
+name = "zlib-rs"
+version = "0.6.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "34b31d188d9d685a4f9c7b46d6e36631b07058d2cfe190267adce54dc230bf12"
+
 [[package]]
 name = "zmij"
 version = "1.0.23"

Cargo.toml

@@ -1,3 +1,11 @@
+[workspace]
+members = [".", "init"]
+
+[profile.release]
+opt-level = "z"
+lto = true
+strip = true
+
 [package]
 name = "slim"
 version = "0.1.0"
@@ -5,7 +13,7 @@ edition = "2024"
 
 [dependencies]
 anyhow = "1.0.104"
-base64 = "0.22"
+base64 = "0.23"
 clap = { version = "4.6.6", features = ["derive"] }
 flate2 = "1.1.9"
 serde = { version = "1.0.229", features = ["derive"] }

example/test.sh

@@ -295,8 +295,63 @@ EOF
     rm -rf "$work"
 }
 
+test_systemd() {
+    echo "=== Testing systemd as init ==="
+
+    work="$(mktemp -d)"
+    img="slim-test-systemd"
+
+    cat > "$work/slim-test.service" <<'SVC'
+[Unit]
+Description=slim systemd test
+After=multi-user.target
+
+[Service]
+Type=oneshot
+ExecStart=/bin/sh -c "echo SYSTEMD_TEST_OK > /dev/console; sleep 1; systemctl poweroff"
+
+[Install]
+WantedBy=multi-user.target
+SVC
+
+    cat > "$work/Containerfile" <<EOF
+FROM archlinux:latest
+COPY slim-test.service /etc/systemd/system/slim-test.service
+RUN mkdir -p /etc/systemd/system/multi-user.target.wants && \
+    ln -sf /etc/systemd/system/slim-test.service \
+       /etc/systemd/system/multi-user.target.wants/slim-test.service
+CMD ["/sbin/init"]
+EOF
+
+    echo "-- Building container image with systemd..."
+    if ! podman build -t "$img" "$work" >/dev/null 2>&1; then
+        report fail "systemd as init (podman build failed)"
+        rm -rf "$work"
+        return
+    fi
+
+    echo "-- Building slim VM..."
+    if ! "$SLIM_BIN" build qcow2 "$img" >/dev/null 2>&1; then
+        report fail "systemd as init (slim build failed)"
+        cleanup "$img" "$img"
+        rm -rf "$work"
+        return
+    fi
+
+    echo "-- Booting VM (systemd as PID 1)..."
+    output=$(timeout "$TIMEOUT" "$SLIM_BIN" run "$img" 2>&1 || true)
+    check_output "$output" "SYSTEMD_TEST_OK" "systemd boots and runs service"
+    check_output "$output" "reboot: Power down" "systemd shuts down cleanly"
+
+    cleanup "$img" "$img"
+    rm -rf "$work"
+}
+
 echo "Building slim..."
 cargo build 2>&1
+cargo build --release -p slim-init --target x86_64-unknown-linux-musl 2>&1
+cp target/x86_64-unknown-linux-musl/release/slim-init \
+   "${XDG_DATA_HOME:-$HOME/.local/share}/slim-rs/slim-init"
 
 test_distro "alpine" "alpine:latest" ""
 test_distro "archlinux" "archlinux:latest" "RUN pacman -Sy --noconfirm iproute2 wget; pacman -Sc --noconfirm"
@@ -307,6 +362,8 @@ test_mount
 
 test_service
 
+test_systemd
+
 echo ""
 echo "=== Results: $pass passed, $fail failed ==="
 [ "$fail" -eq 0 ]

init/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "slim-init"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+base64 = "0.23"
+nix = { version = "0.31", features = ["mount", "fs", "process", "user", "reboot"] }

init/src/main.rs

@@ -0,0 +1,429 @@
+//! slim universal init.
+//!
+//! Injected by `slim build` at /slim/init and invoked via init=/slim/init.
+//! Sets up devices, filesystems, networking, and 9p shares, then execs the
+//! container's CMD/ENTRYPOINT (or a runtime override) with execvp so the
+//! command becomes PID 1 directly.
+
+use base64::Engine;
+use nix::mount::{MsFlags, mount};
+use nix::sys::reboot::{RebootMode, reboot};
+use nix::sys::stat::{Mode, SFlag, makedev, mknod};
+use nix::sys::wait::waitpid;
+use nix::unistd::{ForkResult, Gid, Uid, User, execvp, fork, setgid, setuid};
+use std::env;
+use std::ffi::CString;
+use std::fs;
+use std::os::unix::fs::PermissionsExt;
+use std::path::Path;
+use std::process::Command;
+
+fn warn(msg: &str) {
+    eprintln!("slim-init: {msg}");
+}
+
+/// Run a fallible operation, logging on error.
+fn try_io<F, T>(label: &str, f: F)
+where
+    F: FnOnce() -> std::io::Result<T>,
+{
+    if let Err(e) = f() {
+        warn(&format!("{label}: {e}"));
+    }
+}
+
+/// Run a command, logging on error or non-zero exit.
+fn try_cmd(label: &str, cmd: &mut Command) {
+    match cmd.status() {
+        Ok(status) => {
+            if !status.success() {
+                warn(&format!("{label}: exited with {status}"));
+            }
+        }
+        Err(e) => warn(&format!("{label}: {e}")),
+    }
+}
+
+/// The kernel passes a minimal environment to init. Set a default PATH
+/// so that `ip` and other tools can be found by name.
+fn ensure_path() {
+    if env::var("PATH").is_err() {
+        // SAFETY: we are single-threaded before fork/exec.
+        unsafe {
+            env::set_var(
+                "PATH",
+                "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
+            );
+        }
+    }
+}
+
+fn find_in_path(prog: &str) -> Option<String> {
+    let path = env::var("PATH").ok()?;
+    for dir in path.split(':') {
+        let candidate = format!("{dir}/{prog}");
+        if Path::new(&candidate).exists() {
+            return Some(candidate);
+        }
+    }
+    None
+}
+
+fn try_mount(
+    source: Option<&str>,
+    target: &str,
+    fstype: Option<&str>,
+    flags: MsFlags,
+    data: Option<&str>,
+) {
+    if let Err(e) = mount(source, target, fstype, flags, data) {
+        warn(&format!("mount {target}: {e}"));
+    }
+}
+
+fn setup_filesystems() {
+    if !Path::new("/dev/console").exists() {
+        try_io("mknod /dev/console", || {
+            mknod(
+                "/dev/console",
+                SFlag::S_IFCHR,
+                Mode::S_IRUSR | Mode::S_IWUSR,
+                makedev(5, 1),
+            )
+            .map_err(std::io::Error::from)
+        });
+    }
+
+    let dirs = [
+        "/proc",
+        "/sys",
+        "/dev/pts",
+        "/dev/shm",
+        "/run",
+        "/tmp",
+        "/sys/fs/cgroup",
+    ];
+    for d in &dirs {
+        try_io(&format!("mkdir {d}"), || fs::create_dir_all(d));
+    }
+
+    try_mount(Some("proc"), "/proc", Some("proc"), MsFlags::empty(), None);
+    try_mount(Some("sysfs"), "/sys", Some("sysfs"), MsFlags::empty(), None);
+    try_mount(
+        Some("devpts"),
+        "/dev/pts",
+        Some("devpts"),
+        MsFlags::empty(),
+        None,
+    );
+    try_mount(
+        Some("tmpfs"),
+        "/dev/shm",
+        Some("tmpfs"),
+        MsFlags::empty(),
+        None,
+    );
+    try_mount(
+        Some("tmpfs"),
+        "/run",
+        Some("tmpfs"),
+        MsFlags::empty(),
+        Some("mode=755"),
+    );
+    try_mount(
+        Some("tmpfs"),
+        "/tmp",
+        Some("tmpfs"),
+        MsFlags::empty(),
+        Some("mode=1777"),
+    );
+
+    // cgroup2
+    try_mount(
+        Some("cgroup2"),
+        "/sys/fs/cgroup",
+        Some("cgroup2"),
+        MsFlags::empty(),
+        None,
+    );
+    if let Ok(controllers) = fs::read_to_string("/sys/fs/cgroup/cgroup.controllers") {
+        for c in controllers.split_whitespace() {
+            try_io("write cgroup.subtree_control", || {
+                fs::write("/sys/fs/cgroup/cgroup.subtree_control", format!("+{c}"))
+            });
+        }
+    }
+}
+
+fn setup_rootless_prereqs() {
+    // make-rshared /
+    if let Err(e) =
+        mount::<str, str, str, str>(None, "/", None, MsFlags::MS_REC | MsFlags::MS_SHARED, None)
+    {
+        warn(&format!("make-rshared /: {e}"));
+    }
+
+    // chmod u+s newuidmap newgidmap
+    for bin in &["/usr/bin/newuidmap", "/usr/bin/newgidmap"] {
+        match fs::metadata(bin) {
+            Ok(meta) => {
+                let mut perms = meta.permissions();
+                perms.set_mode(perms.mode() | 0o4000);
+                try_io(&format!("chmod u+s {bin}"), || {
+                    fs::set_permissions(bin, perms)
+                });
+            }
+            Err(e) if e.kind() == std::io::ErrorKind::NotFound => {}
+            Err(e) => warn(&format!("stat {bin}: {e}")),
+        }
+    }
+}
+
+fn setup_timezone() {
+    try_io("symlink timezone", || {
+        std::os::unix::fs::symlink("/usr/share/zoneinfo/Europe/Stockholm", "/etc/localtime")
+    });
+}
+
+fn setup_networking() {
+    let ip = find_in_path("ip").unwrap_or_else(|| "/sbin/ip".to_string());
+    try_cmd(
+        "ip link set lo up",
+        Command::new(&ip).args(["link", "set", "lo", "up"]),
+    );
+    try_cmd(
+        "ip link set eth0 up",
+        Command::new(&ip).args(["link", "set", "eth0", "up"]),
+    );
+    try_cmd(
+        "ip addr add 10.0.2.15/24 dev eth0",
+        Command::new(&ip).args(["addr", "add", "10.0.2.15/24", "dev", "eth0"]),
+    );
+    try_cmd(
+        "ip route add default via 10.0.2.2",
+        Command::new(&ip).args(["route", "add", "default", "via", "10.0.2.2"]),
+    );
+    try_io("write /etc/resolv.conf", || {
+        fs::write("/etc/resolv.conf", "nameserver 10.0.2.3\n")
+    });
+}
+
+fn setup_9p_shares(workdir: &str) {
+    let cmdline = match fs::read_to_string("/proc/cmdline") {
+        Ok(c) => c,
+        Err(e) => {
+            warn(&format!("read /proc/cmdline: {e}"));
+            return;
+        }
+    };
+    let b64 = base64::engine::general_purpose::STANDARD;
+
+    for tok in cmdline.split_whitespace() {
+        if let Some(rest) = tok.strip_prefix("slim.mount=") {
+            let Some((tag, dest_b64)) = rest.split_once(':') else {
+                continue;
+            };
+            let dest = match b64.decode(dest_b64) {
+                Ok(bytes) => match String::from_utf8(bytes) {
+                    Ok(s) => s,
+                    Err(e) => {
+                        warn(&format!("9p: invalid UTF-8 in guest path: {e}"));
+                        continue;
+                    }
+                },
+                Err(e) => {
+                    warn(&format!("9p: base64 decode failed: {e}"));
+                    continue;
+                }
+            };
+
+            // Resolve relative guest paths against WORKINGDIR
+            let dest = if dest.starts_with('/') {
+                dest
+            } else {
+                format!("{}/{}", workdir, dest)
+            };
+
+            try_io(&format!("mkdir {dest}"), || fs::create_dir_all(&dest));
+            try_mount(
+                Some(tag),
+                &dest,
+                Some("9p"),
+                MsFlags::empty(),
+                Some("trans=virtio,version=9p2000.L"),
+            );
+        }
+    }
+}
+
+fn read_file_opt(path: &str) -> Option<String> {
+    fs::read_to_string(path)
+        .ok()
+        .filter(|s| !s.trim().is_empty())
+}
+
+fn split_null_delimited(data: &[u8]) -> Vec<String> {
+    data.split(|&b| b == 0)
+        .filter(|s| !s.is_empty())
+        .map(|s| String::from_utf8_lossy(s).into_owned())
+        .collect()
+}
+
+fn read_argv() -> Vec<String> {
+    // Check for runtime override: slim.cmd=<base64(null-delimited argv)>
+    let b64 = base64::engine::general_purpose::STANDARD;
+    if let Ok(cmdline) = fs::read_to_string("/proc/cmdline") {
+        for tok in cmdline.split_whitespace() {
+            if let Some(rest) = tok.strip_prefix("slim.cmd=")
+                && let Ok(decoded) = b64.decode(rest)
+            {
+                let argv = split_null_delimited(&decoded);
+                if !argv.is_empty() {
+                    return argv;
+                }
+            }
+        }
+    }
+
+    // Fall back to build-time argv from /slim/exec
+    match fs::read("/slim/exec") {
+        Ok(data) => {
+            let argv = split_null_delimited(&data);
+            if !argv.is_empty() {
+                return argv;
+            }
+        }
+        Err(e) => warn(&format!("read /slim/exec: {e}")),
+    }
+
+    warn("no command found, falling back to /bin/sh");
+    vec!["/bin/sh".to_string()]
+}
+
+fn apply_env() {
+    if let Ok(data) = fs::read("/slim/env") {
+        for entry in split_null_delimited(&data) {
+            if let Some((key, val)) = entry.split_once('=') {
+                // SAFETY: we are single-threaded before fork/exec.
+                unsafe { env::set_var(key, val) };
+            }
+        }
+    }
+}
+
+fn apply_workdir() {
+    if let Some(dir) = read_file_opt("/slim/workdir") {
+        try_io("set working directory", || env::set_current_dir(&dir));
+    }
+}
+
+struct UserSpec {
+    uid: Uid,
+    gid: Gid,
+}
+
+fn resolve_user(spec: &str) -> Option<UserSpec> {
+    let (user_part, gid_part) = match spec.split_once(':') {
+        Some((u, g)) => (u, Some(g)),
+        None => (spec, None),
+    };
+
+    let (uid, default_gid) = if let Ok(numeric) = user_part.parse::<u32>() {
+        let user = User::from_uid(Uid::from_raw(numeric)).ok().flatten();
+        let gid = user
+            .as_ref()
+            .map(|u| u.gid)
+            .unwrap_or(Gid::from_raw(numeric));
+        (Uid::from_raw(numeric), gid)
+    } else {
+        let user = User::from_name(user_part).ok().flatten()?;
+        (user.uid, user.gid)
+    };
+
+    let gid = match gid_part {
+        Some(g) => match g.parse::<u32>() {
+            Ok(n) => Gid::from_raw(n),
+            Err(_) => default_gid,
+        },
+        None => default_gid,
+    };
+
+    Some(UserSpec { uid, gid })
+}
+
+fn exec_command(argv: &[String], user: Option<UserSpec>) -> ! {
+    let cstrings: Vec<CString> = argv
+        .iter()
+        .map(|s| CString::new(s.as_str()).unwrap_or_default())
+        .collect();
+    let c_prog = cstrings[0].clone();
+    let c_refs: Vec<&CString> = cstrings.iter().collect();
+
+    match user {
+        None => {
+            // No privilege drop: exec directly, PID 1 becomes the command.
+            let Err(e) = execvp(&c_prog, &c_refs);
+            warn(&format!("execvp {}: {e}", argv[0]));
+            let _ = reboot(RebootMode::RB_POWER_OFF);
+            std::process::exit(1);
+        }
+        Some(user) => {
+            // Drop privileges in a child so PID 1 (root) can poweroff afterwards.
+            match unsafe { fork() } {
+                Ok(ForkResult::Child) => {
+                    // setgid before setuid to avoid losing privileges
+                    if let Err(e) = setgid(user.gid) {
+                        warn(&format!("setgid: {e}"));
+                    }
+                    if let Err(e) = setuid(user.uid) {
+                        warn(&format!("setuid: {e}"));
+                    }
+                    let Err(e) = execvp(&c_prog, &c_refs);
+                    warn(&format!("execvp {}: {e}", argv[0]));
+                    std::process::exit(127);
+                }
+                Ok(ForkResult::Parent { child }) => {
+                    let _ = waitpid(child, None);
+                    let _ = reboot(RebootMode::RB_POWER_OFF);
+                    std::process::exit(0);
+                }
+                Err(e) => {
+                    warn(&format!("fork: {e}"));
+                    let _ = reboot(RebootMode::RB_POWER_OFF);
+                    std::process::exit(1);
+                }
+            }
+        }
+    }
+}
+
+fn main() {
+    ensure_path();
+
+    // === Devices & special filesystems ===
+    setup_filesystems();
+
+    // === Rootless container prerequisites (best-effort) ===
+    setup_rootless_prereqs();
+
+    // === Timezone ===
+    setup_timezone();
+
+    // === Networking ===
+    setup_networking();
+
+    // === 9p shares ===
+    let workdir = read_file_opt("/slim/workdir").unwrap_or_default();
+    setup_9p_shares(&workdir);
+
+    // === Environment & working directory ===
+    apply_env();
+    apply_workdir();
+
+    // === Resolve user for privilege drop ===
+    let user = read_file_opt("/slim/user").and_then(|spec| resolve_user(&spec));
+
+    // === Execute the configured command ===
+    let argv = read_argv();
+    exec_command(&argv, user);
+}

src/build.rs

@@ -75,12 +75,14 @@ fn build_inner(
     cmd: Option<String>,
 ) -> Result<()> {
     let config = inject::inspect_config(image)?;
-    let command = cmd.unwrap_or_else(|| inject::infer_command(&config));
+    let argv = match cmd {
-    let exec_script =
+        Some(s) => vec!["/bin/sh".into(), "-c".into(), s],
-        inject::build_exec_script(&command, &config.env, config.working_dir.as_deref());
+        None => inject::infer_argv(&config),
+    };
     inject::inject(
         mount_path,
-        &exec_script,
+        &argv,
+        &config.env,
         config.user.as_deref(),
         config.working_dir.as_deref(),
     )?;

src/inject.rs

@@ -1,15 +1,14 @@
-//! Inject: inspect a podman image's config, infer the default command, and
+//! Inject: inspect a podman image's config, infer the default command argv,
-//! inject distro-agnostic /slim/ scripts (init + exec) into the mounted rootfs.
+//! and inject the slim init binary + null-delimited argv/env files into the
+//! mounted rootfs.
 
 use anyhow::{Context, Result, anyhow};
 use serde::Deserialize;
-use std::fmt::Write as _;
 use std::fs;
 use std::path::Path;
 
 use crate::command::cmd;
-
+use crate::registry::init_binary_path;
-const SLIM_INIT: &str = include_str!("scripts/slim-init.sh");
 
 #[derive(Debug, Default, Deserialize)]
 #[serde(rename_all = "PascalCase")]
@@ -40,56 +39,38 @@ pub fn inspect_config(image: &str) -> Result<Config> {
     Ok(config)
 }
 
-/// Infer the command string from the image config.
+/// Infer the command argv from the image config.
 ///
 /// Concatenates ENTRYPOINT + CMD (Docker semantics). If neither is present,
-/// falls back to `/bin/sh`.
+/// falls back to `["/bin/sh"]`.
-pub fn infer_command(config: &Config) -> String {
+pub fn infer_argv(config: &Config) -> Vec<String> {
-    let parts = config.entrypoint.iter().chain(config.cmd.iter());
+    let parts: Vec<String> = config
-    let parts: Vec<_> = parts.map(|s| s.as_str()).collect();
+        .entrypoint
-
-    match &parts[..] {
-        [] => "/bin/sh".into(),
-        ["/bin/sh" | "sh", "-c", cmd] => cmd.to_string(),
-        _ => shell_join(&parts),
-    }
-}
-
-fn shell_escape(s: &str) -> String {
-    format!("'{}'", s.replace('\'', "'\\''"))
-}
-
-fn shell_join(parts: &[&str]) -> String {
-    parts
         .iter()
-        .map(|p| shell_escape(p))
+        .chain(config.cmd.iter())
-        .collect::<Vec<_>>()
+        .cloned()
-        .join(" ")
+        .collect();
+
+    if parts.is_empty() {
+        vec!["/bin/sh".into()]
+    } else {
+        parts
+    }
 }
 
-/// Generate the /slim/exec script from a command string, env vars, and working dir.
+/// Join items as null-delimited bytes.
-pub fn build_exec_script(command: &str, env: &[String], working_dir: Option<&str>) -> String {
+pub fn null_delimited(items: &[String]) -> Vec<u8> {
-    let mut lines = String::from("#!/bin/sh\n");
+    let mut data = Vec::new();
-    if let Some(dir) = working_dir.filter(|d| !d.is_empty()) {
+    for item in items {
-        _ = writeln!(&mut lines, "cd {} 2>/dev/null", shell_escape(dir));
+        data.extend_from_slice(item.as_bytes());
+        data.push(0);
     }
-    for var in env {
+    data
-        if let Some((key, val)) = var.split_once('=') {
-            _ = writeln!(
-                &mut lines,
-                "export {}={}",
-                shell_escape(key),
-                shell_escape(val)
-            );
-        }
-    }
-    _ = writeln!(&mut lines, "exec /bin/sh -c {}", shell_escape(command));
-    lines
 }
 
 /// Install `content` into the mounted rootfs at `<mount>/slim/<name>` with
 /// the given mode.
-fn install_into_rootfs(mount: &str, name: &str, mode: &str, content: &str) -> Result<()> {
+fn install_into_rootfs(mount: &str, name: &str, mode: &str, content: &[u8]) -> Result<()> {
     let temp = tempfile::NamedTempFile::new()?;
     fs::write(temp.path(), content)?;
     let src = temp.path().to_str().context("temp path is not UTF-8")?;
@@ -100,25 +81,34 @@ fn install_into_rootfs(mount: &str, name: &str, mode: &str, content: &str) -> Re
     Ok(())
 }
 
-/// Inject /slim/init, /slim/exec, and optionally /slim/user and /slim/workdir
+/// Inject /slim/init (binary), /slim/exec (null-delimited argv), /slim/env
-/// into a mounted container image rootfs.
+/// (null-delimited env), and optionally /slim/user and /slim/workdir into a
+/// mounted container image rootfs.
 pub fn inject(
     mount_path: &Path,
-    exec_script: &str,
+    argv: &[String],
+    env: &[String],
     user: Option<&str>,
     working_dir: Option<&str>,
 ) -> Result<()> {
     let mount_str = mount_path.to_str().context("mount path is not UTF-8")?;
 
-    install_into_rootfs(mount_str, "init", "755", SLIM_INIT)?;
+    let init_binary = fs::read(init_binary_path()?).context("Failed to read slim-init binary")?;
-    install_into_rootfs(mount_str, "exec", "755", exec_script)?;
+    let exec_data = null_delimited(argv);
+    let env_data = null_delimited(env);
+
+    install_into_rootfs(mount_str, "init", "755", &init_binary)?;
+    install_into_rootfs(mount_str, "exec", "644", &exec_data)?;
+    if !env_data.is_empty() {
+        install_into_rootfs(mount_str, "env", "644", &env_data)?;
+    }
 
     if let Some(user) = user.filter(|u| !u.is_empty()) {
-        install_into_rootfs(mount_str, "user", "644", user)?;
+        install_into_rootfs(mount_str, "user", "644", user.as_bytes())?;
     }
 
     if let Some(dir) = working_dir.filter(|d| !d.is_empty()) {
-        install_into_rootfs(mount_str, "workdir", "644", dir)?;
+        install_into_rootfs(mount_str, "workdir", "644", dir.as_bytes())?;
     }
 
     Ok(())

src/qemu.rs

@@ -85,7 +85,9 @@ pub(crate) fn run(
     }
 
     if let Some(cmd) = &cmd {
-        let encoded = base64::engine::general_purpose::STANDARD.encode(cmd.as_bytes());
+        let argv = ["/bin/sh".to_string(), "-c".to_string(), cmd.clone()];
+        let data: Vec<u8> = argv.join("\0").into_bytes();
+        let encoded = base64::engine::general_purpose::STANDARD.encode(&data);
         cmdline.push(format!("slim.cmd={encoded}"));
     }
 

src/registry.rs

@@ -32,6 +32,12 @@ pub(crate) fn registry_base_dir() -> Result<PathBuf> {
         .context("Failed to create XDG_DATA_HOME subdirectory")
 }
 
+pub(crate) fn init_binary_path() -> Result<PathBuf> {
+    let base = xdg::BaseDirectories::with_prefix("slim-rs");
+    base.get_data_file("slim-init")
+        .context("slim-init not found in XDG data dir")
+}
+
 pub(crate) fn registry_dir(image: &str) -> Result<PathBuf> {
     validate_image_name(image)?;
     let base = registry_base_dir()?;

src/scripts/slim-init.sh

@@ -1,121 +0,0 @@
-#!/bin/sh
-# slim universal init - distro-agnostic VM bootstrap.
-# Injected by `slim build` at /slim/init and invoked via init=/slim/init.
-
-# === Helpers ===
-b64dec() {
-    printf '%s' "$1" | base64 -d 2>/dev/null || printf '%s' "$1" | openssl base64 -d 2>/dev/null
-}
-
-# === Devices & special filesystems ===
-[ -c /dev/console ] || mknod -m 600 /dev/console c 5 1
-mkdir -p /proc /sys /dev/pts /dev/shm
-mount -t proc proc /proc
-mount -t sysfs sysfs /sys
-mount -t devpts devpts /dev/pts
-mount -t tmpfs tmpfs /dev/shm
-mount -t tmpfs tmpfs /run  -o mode=755
-mount -t tmpfs tmpfs /tmp  -o mode=1777
-
-# === cgroup2 ===
-mkdir -p /sys/fs/cgroup
-mount -t cgroup2 none /sys/fs/cgroup 2>/dev/null || echo "mount cgroup2 failed"
-# shellcheck disable=SC2013 # word-splitting is intentional: controllers are space-separated
-for c in $(cat /sys/fs/cgroup/cgroup.controllers 2>/dev/null); do
-    echo "+$c" > /sys/fs/cgroup/cgroup.subtree_control 2>/dev/null || echo "enable cgroup controller $c failed"
-done
-
-# === Rootless container prerequisites (best-effort) ===
-mount --make-rshared / 2>/dev/null || echo "make-rshared / failed"
-chmod u+s /usr/bin/newuidmap /usr/bin/newgidmap 2>/dev/null || echo "chmod newuidmap/newgidmap failed"
-
-# === Timezone ===
-ln -sf /usr/share/zoneinfo/Europe/Stockholm /etc/localtime 2>/dev/null || echo "set timezone failed"
-
-# === Networking (QEMU slirp: guest 10.0.2.15/24, gw 10.0.2.2, dns 10.0.2.3) ===
-ip link set lo up 2>/dev/null || echo "ip link set lo up failed"
-ip link set eth0 up 2>/dev/null || echo "ip link set eth0 up failed"
-ip addr add 10.0.2.15/24 dev eth0 2>/dev/null || echo "ip addr add eth0 failed"
-ip route add default via 10.0.2.2 2>/dev/null || echo "ip route add default failed"
-echo nameserver 10.0.2.3 > /etc/resolv.conf
-
-# === 9p shares (host directories shared via --mount) ===
-# Each share is passed as slim.mount=<tag>:<base64(guest_path)> on the
-# kernel cmdline.  The 9p tag is short (e.g. slim0) because mount_tag
-# has a ~31-byte limit; the guest path is base64-encoded.
-# Non-absolute guest paths are resolved against /slim/workdir (the
-# image's WORKINGDIR).
-SLIM_WORKDIR=""
-[ -f /slim/workdir ] && SLIM_WORKDIR=$(cat /slim/workdir 2>/dev/null)
-# shellcheck disable=SC2013 # word-splitting is intentional: cmdline tokens are space-separated
-for tok in $(cat /proc/cmdline 2>/dev/null); do
-    case "$tok" in
-        slim.mount=*)
-            v=${tok#slim.mount=}
-            tag=${v%%:*}
-            dest_b64=${v#*:}
-            dest=$(b64dec "$dest_b64") || echo "base64 decode failed"
-            if [ -n "$tag" ] && [ -n "$dest" ]; then
-                # Resolve relative paths against the image's WORKINGDIR
-                case "$dest" in
-                    /*) ;;
-                    *) dest="${SLIM_WORKDIR:-/}/${dest}" ;;
-                esac
-                mkdir -p "$dest"
-                mount -t 9p "$tag" "$dest" -o trans=virtio,version=9p2000.L 2>/dev/null \
-                    && echo "mounted 9p '$tag' -> '$dest'" \
-                    || echo "failed to mount 9p '$tag' -> '$dest'"
-            fi
-            ;;
-    esac
-done
-
-# === Drop privileges (respect USER directive from image config) ===
-# /slim/user may contain a username, uid, or uid:gid (OCI image spec).
-# Numeric uids are resolved to a username via /etc/passwd because BusyBox
-# su does not accept numeric arguments.
-SLIM_USER=""
-[ -f /slim/user ] && SLIM_USER=$(cat /slim/user 2>/dev/null)
-
-# Resolve a numeric uid to a username from /etc/passwd.
-slim_resolve_user() {
-    _u="$1"
-    case "$_u" in
-        *[!0-9]*) printf '%s' "$_u" ;;
-        *)
-            _resolved=$(awk -F: -v uid="$_u" '$3==uid{print $1; exit}' /etc/passwd 2>/dev/null)
-            [ -n "$_resolved" ] && printf '%s' "$_resolved" || printf '%s' "$_u"
-            ;;
-    esac
-}
-
-# Exec a command, dropping privileges if SLIM_USER is set.
-# When dropping privileges, run as a child (not exec) so PID 1 stays root
-# and can poweroff after the command exits — non-root cannot call poweroff.
-slim_exec() {
-    _cmd="$1"
-    if [ -z "$SLIM_USER" ]; then
-        exec /bin/sh -c "$_cmd"
-    fi
-    _user="${SLIM_USER%%:*}"
-    _user=$(slim_resolve_user "$_user")
-    su "$_user" -c "$_cmd"
-    poweroff -f
-}
-
-# === Execute the configured command ===
-# If slim.cmd=<base64> is on the kernel cmdline, decode and exec it.
-# Otherwise, exec /slim/exec (generated from the image's CMD/ENTRYPOINT).
-# shellcheck disable=SC2013 # word-splitting is intentional: cmdline tokens are space-separated
-for tok in $(cat /proc/cmdline 2>/dev/null); do
-    case "$tok" in
-        slim.cmd=*)
-            v=${tok#slim.cmd=}
-            decoded=$(b64dec "$v") || echo "base64 decode failed"
-            if [ -n "$decoded" ]; then
-                slim_exec "$decoded"
-            fi
-            ;;
-    esac
-done
-slim_exec "/slim/exec"