diff --git a/cmd/env b/cmd/env
index cb27fc3..08b0fa3 100644
--- a/cmd/env
+++ b/cmd/env
@@ -52,9 +52,7 @@ _env() {
     _require_program socat
 
     exampledir="${BASEDIR}/examples/vm"
-    if [[ ! -d ${exampledir} ]]; then
-      _fatal 1 "Example dir (${exampledir}) not found."
-    fi
+    _require_path "${exampledir}"
 
     if [ ! -d "${bootstrap_dir}" ]; then
       if ! mkdir --parent ${verbose} "${bootstrap_dir}"; then
diff --git a/cmd/run b/cmd/run
index 81b087a..2951f20 100644
--- a/cmd/run
+++ b/cmd/run
@@ -49,11 +49,7 @@ _run() {
   while true; do
     case "$1" in
       '-k' | '--kernel-dir' )
-        local kernel_dir="$2"; shift 2
-
-        if [[ ! -d "$kernel_dir" ]]; then
-          _fatal 1 "no such directory: '$kernel_dir'"
-        fi
+        local kernel_dir="$2" ; shift 2
         ;;
 
       '-c' | '--cloud-init' )
@@ -145,8 +141,9 @@ _run() {
   QEMU_PARAMS+=("-pidfile" "${VMROOT}/run/${VMNAME}/pidfile")
 
   if [[ -v kernel_dir ]]; then
-    qemu_kern_add_custom --kernel-dir "${kernel_dir}"
+    GUEST_KERNEL_CUSTOM_DIR="${kernel_dir}"
   fi
+  qemu_kernel_setup
 
   if [[ -v do_background ]]; then
     QEMU_PARAMS+=("-daemonize")
diff --git a/common/rc b/common/rc
index 3222a5a..5c1c7f7 100644
--- a/common/rc
+++ b/common/rc
@@ -130,13 +130,21 @@ _require_program() {
 }
 
 _require_path() {
-  local rpath="$1"; shift
+  local rpath="$1"
 
   if [[ ! -d "${rpath}" ]]; then
     _fatal 1 "Path not found (${rpath}). $*"
   fi
 }
 
+_require_vars() {
+  for var in $1; do
+    if [[ ! -v ${var} ]]; then
+      _fatal 1 "${FUNCNAME[0]} Missing var ${var}. Missing in ${VMCONFIG}?"
+    fi
+  done
+}
+
 _is_running() {
   if [[ -f "${VMRUN}/pidfile" ]]; then
     return 0
diff --git a/common/shellcheck b/common/shellcheck
index 73629e8..c585dfb 100644
--- a/common/shellcheck
+++ b/common/shellcheck
@@ -6,5 +6,9 @@
 
 # suppress unused global variable warnings
 _silence_sc2034() {
-  echo "$QEMU_SYSTEM_BINARY $QEMU_TRACE_EVENTS ${GUEST_KERNEL_CMDLINE[*]} $RESET" > /dev/null
+  echo "$QEMU_SYSTEM_BINARY \
+    $QEMU_TRACE_EVENTS \
+    ${GUEST_KERNEL_CMDLINE[*]} \
+    $RESET \
+    $GUEST_KERNEL_CUSTOM_DIR " > /dev/null
 }
diff --git a/lib/qemu/kern b/lib/qemu/kern
index 333f012..6e8dde3 100644
--- a/lib/qemu/kern
+++ b/lib/qemu/kern
@@ -5,13 +5,7 @@
 # Written by Joel Granados <joel.granados@kernel.org>
 
 _qemu_kern_img_add() {
-  local cmdline_extra="$1"
-
-  for var in GUEST_BOOT GUEST_BOOT_BASE; do
-    if [[ ! -v ${var} ]]; then
-      _fatal 1 "${FUNCNAME[0]} Missing var ${var}. Add it to ${VMCONFIG}"
-    fi
-  done
+  _require_vars "GUEST_BOOT GUEST_BOOT_BASE"
 
   if [[ ! -f "${VMROOT}/$GUEST_BOOT" ]]; then
     if [[ ! -f "${VMROOT}/$GUEST_BOOT_BASE" ]]; then
@@ -27,66 +21,33 @@ _qemu_kern_img_add() {
     GUEST_KERNEL_BOOTDEV="/dev/vda1"
   fi
 
-  local cmdline="root=${GUEST_KERNEL_BOOTDEV} console=${GUEST_KERNEL_CONSOLE} ${cmdline_extra}"
-  if [[ -v GUEST_KERNEL_APPEND_EXTRA ]]; then
-    cmdline="$cmdline ${GUEST_KERNEL_APPEND_EXTRA}"
-  fi
-
-  QEMU_PARAMS+=("-kernel" "${kernel_dir}/${GUEST_KERNEL_IMAGE}")
-  QEMU_PARAMS+=("-append" "$cmdline")
+  QEMU_PARAMS+=("-kernel" "${GUEST_KERNEL_CUSTOM_DIR}/${GUEST_KERNEL_IMAGE}")
+  QEMU_PARAMS+=("-append" \
+    "root=${GUEST_KERNEL_BOOTDEV} console=${GUEST_KERNEL_CONSOLE} ${GUEST_KERNEL_APPEND_EXTRA}")
 }
 
-qemu_kern_add_custom() {
-  local cmdline_extra=""
-  local mod_share="9p"
-  local long="kernel-dir:,cmdline-extra:,mod-share:"
-
-  if ! tmp=$(getopt -o "" --long "$long" -n "${FUNCNAME[0]}" -- "$@"); then
-    exit 1
-  fi
-
-  eval set -- "$tmp"
-  unset tmp
-
-  while true; do
-    case "$1" in
-      '--kernel-dir' )
-        local kernel_dir="$2"; shift 2
-        ;;
-      '--cmdline-extra' )
-        cmdline_extra="${cmdline_extra} $2"; shift 2
-        ;;
-      'mod-share' )
-        mod_share="$2"; shift 2
-        ;;
-      '--' )
-        shift; break
-        ;;
-      * )
-        _fatal 1 "unknown argument '$1'"
-        ;;
-    esac
-  done
-
-  if [[ ! -v kernel_dir ]]; then
-    _fatal 1 "${FUNCNAME[0]} Missing required --kernel-dir argument"
+qemu_kernel_setup() {
+  if [[ ! -v GUEST_KERNEL_CUSTOM_DIR ]]; then
+    # Yes!; Do nothing with image-backed
+    if [[ -v NIX_STORE_PATH ]]; then
+      _require_vars "GUEST_KERNEL_IMAGE GUEST_KERNEL_CONSOLE"
+      qemu_nix_add_noimgnix
+    fi
+    return
   fi
 
-  for var in GUEST_KERNEL_IMAGE GUEST_KERNEL_CONSOLE; do
-    if [[ ! -v ${var} ]]; then
-      _fatal 1 "${FUNCNAME[0]} Missing var ${var}. Add it to ${VMCONFIG}"
-    fi
-  done
+  _require_path "${GUEST_KERNEL_CUSTOM_DIR}"
+  _require_vars "GUEST_KERNEL_IMAGE GUEST_KERNEL_CONSOLE"
 
   if [[ -v NIX_STORE_PATH ]]; then
     qemu_nix_add_noimgnix
+    local mod_share="virtiofs"
   else
-    _qemu_kern_img_add "${cmdline_extra}"
+    _qemu_kern_img_add
+    local mod_share="9p"
   fi
 
-  local kernel_tag="kernel_dir"
-  qemu_share_add --shared-dir "${kernel_dir}" \
-    --tag "${kernel_tag}" \
+  qemu_share_add --shared-dir "${GUEST_KERNEL_CUSTOM_DIR}" \
+    --tag "kernel_dir" \
     --share-type "${mod_share}"
 }
-
diff --git a/lib/qemu/nix b/lib/qemu/nix
index 200e1e1..0bddfeb 100644
--- a/lib/qemu/nix
+++ b/lib/qemu/nix
@@ -7,7 +7,7 @@
 _qemu_nix_create_nix_sys () {
   local dst_path="$1"
   local flake_attr_path="nixosConfigurations.vm.config.system.build.toplevel"
-  local flake_dst_dir="${VMSTATE}"
+  local flake_dst_dir="${VMSTATE}/nixstage"
   local flake_dst_path="${flake_dst_dir}/flake.nix"
 
   : "${NIX_FLAKE_PATH:="${BASEDIR}/contrib/nix/x86_64-noimgnix-base.nix"}"
@@ -15,18 +15,13 @@ _qemu_nix_create_nix_sys () {
     _fatal 1 "${FUNCNAME[0]}: File not found (${NIX_FLAKE_PATH})"
   fi
 
-  if ! cp -f "${NIX_FLAKE_PATH}" "${flake_dst_path}"; then
-    _fatal 1 "${FUNCNAME[0]}: Error copying \
-      src:(${NIX_FLAKE_PATH}) dest:(${flake_dst_path})"
-  fi
+  _add_pre_cmd "mkdir -p \"${flake_dst_dir}\""
+  _add_pre_cmd "cp -f \"${NIX_FLAKE_PATH}\" \"${flake_dst_path}\""
 
-  local nix_build_cmd="nix build \
+  _add_pre_cmd "nix build \
     'path:${flake_dst_dir}#${flake_attr_path}' \
     -o \"${dst_path}\" \
     --no-write-lock-file"
-  if ! eval "${nix_build_cmd}"; then
-    _fatal 1 "${FUNCNAME[0]}: Error running '${nix_build_cmd}'"
-  fi
 }
 
 _qemu_nix_create_nix_init () {
@@ -41,89 +36,55 @@ _qemu_nix_create_nix_init () {
 
   local make_path="${state_dir}/Makefile"
   if [[ ! -f ${make_path} ]]; then
-    if ! ln -s "${BASEDIR}/contrib/nix/Makefile" "${make_path}"; then
-      _fatal 1 "${FUNCNAME[0]}: Error creating sym link for ${make_path}"
-    fi
+    _add_pre_cmd "ln -s \"${BASEDIR}/contrib/nix/Makefile\" \"${make_path}\""
   fi
 
   local c_init_path="${state_dir}/vmctl_init.c"
   if [[ ! -f ${c_init_path} ]]; then
-    if ! ln -s "${BASEDIR}/contrib/nix/vmctl_init.c" "${c_init_path}"; then
-      _fatal 1 "${FUNCNAME[0]}: Error creating sym link for ${c_init_path}"
-    fi
+    _add_pre_cmd "ln -s \"${BASEDIR}/contrib/nix/vmctl_init.c\" \"${c_init_path}\""
   fi
 
   if [[ ${NIX_INIT_REBUILD} == "yes" ]]; then
-    if ! make -C "${state_dir}" clean; then
-      _fatal 1 "${FUNCNAME[0]}: Error cleaning ${c_init_path}"
-    fi
-  fi
-  if ! make -C "${state_dir}" all; then
-    _fatal 1 "${FUNCNAME[0]}: Error compiling ${c_init_path}"
+    _add_pre_cmd "make -C \"${state_dir}\" clean"
   fi
+
+  _add_pre_cmd "make -C \"${state_dir}\" all"
 }
 
 qemu_nix_add_noimgnix () {
   _require_program nix
   _require_path "${NIX_STORE_PATH}"
+  _require_vars "VMSTATE"
 
-  local long="cmd-line-extra:"
-
-  if ! tmp=$(getopt -o "" --long "$long" -n "${FUNCNAME[0]}" -- "$@"); then
-    exit 1
-  fi
-
-  eval set -- "$tmp"
-  unset tmp
-
-  local cmd_line_extra=""
-  while true; do
-    case "$1" in
-      '--cmd-line-extra' )
-        cmd_line_extra="$2"; shift 2
-        ;;
-      '--' )
-        shift; break
-        ;;
-      * )
-        _fatal 1 "unknown argument '$1'"
-        ;;
-    esac
-  done
-
-  if [[ ! -v VMSTATE ]]; then
-    _fatal 1 "${FUNCNAME[0]}: VMSTATE global var is not set"
-  fi
-
-  local dst_path="${VMSTATE}/nixsys"
+  local nixsys_link="${VMSTATE}/nixsys"
+  local nixsys_path=""; nixsys_path="$(readlink -f "${nixsys_link}")"
   : "${NIX_SYS_BUILD_FORCE:="no"}" # defaults to "no" if not set
-  if [[ ${NIX_SYS_BUILD_FORCE} == "yes" || ! -h ${dst_path} ]]; then
-    _qemu_nix_create_nix_sys "${dst_path}"
+  if [[ ${NIX_SYS_BUILD_FORCE} == "yes" || ! -h ${nixsys_link} ]]; then
+    _qemu_nix_create_nix_sys "${nixsys_link}"
   fi
 
-  _qemu_nix_create_nix_init "${VMSTATE}"
-
   qemu_share_add --shared-dir "${NIX_STORE_PATH}" \
       --tag "nixstore" \
       --share-type "virtiofs" \
       --vm-dir "/nix/store"
 
-  local nix_init_path=""
-  nix_init_path="$(readlink "${dst_path}")/init"
-  local cmd_line="root=/dev/ram0 console=${GUEST_KERNEL_CONSOLE}"
-  if [[ -v GUEST_KERNEL_APPEND_EXTRA ]]; then
-    cmd_line="${cmd_line} ${GUEST_KERNEL_APPEND_EXTRA}"
+  _qemu_nix_create_nix_init "${VMSTATE}"
+
+  if [[ -v GUEST_KERNEL_CUSTOM_DIR ]]; then
+    QEMU_PARAMS+=("-kernel" "${GUEST_KERNEL_CUSTOM_DIR}/${GUEST_KERNEL_IMAGE}")
+    QEMU_PARAMS+=("-initrd" "${VMSTATE}/init.img")
+  else
+    _fatal 1 "${FUNCNAME[0]}: Running a nixvm without a kernel is unsupported"
   fi
-  cmd_line="${cmd_line} ${cmd_line_extra}"
-  cmd_line="${cmd_line} -- --init-path ${nix_init_path}"
+
+  local cmd_line="root=/dev/ram0 console=${GUEST_KERNEL_CONSOLE}"
+  cmd_line="${cmd_line} ${GUEST_KERNEL_APPEND_EXTRA}"
+  cmd_line="${cmd_line} -- --init-path ${nixsys_path}/init"
   if [[ -v NIX_MOUNTS ]]; then
     for nmount in "${NIX_MOUNTS[@]}"; do
       cmd_line="${cmd_line} --mount ${nmount}"
     done
   fi
 
-  QEMU_PARAMS+=("-kernel" "${kernel_dir}/${GUEST_KERNEL_IMAGE}")
   QEMU_PARAMS+=("-append" "${cmd_line}")
-  QEMU_PARAMS+=("-initrd" "${VMSTATE}/init.img")
-
 }
diff --git a/lib/qemu/share b/lib/qemu/share
index 4cb375f..5d21276 100644
--- a/lib/qemu/share
+++ b/lib/qemu/share
@@ -6,9 +6,7 @@
 
 _qemu_share_force_memshare() {
   # memshare for virtiofs https://virtio-fs.gitlab.io/howto-qemu.html
-  if [[ ! -v GUEST_MEMORY ]]; then
-    _fatal 1 "${FUNCNAME[0]}: GUEST_MEMORY variable is undefined"
-  fi
+  _require_vars "GUEST_MEMORY"
 
   if [[ "${QEMU_PARAMS[*]}" != *"memory-backend-file"* ]]; then
     QEMU_PARAMS+=("-object" "memory-backend-file,id=mem,size=${GUEST_MEMORY},mem-path=/dev/shm,share=on")
@@ -79,9 +77,7 @@ qemu_share_add() {
     _fatal 1 "${FUNCNAME[0]}: missing required '--shared-dir' argument"
   fi
 
-  if [[ ! -d ${shared_dir} ]]; then
-    _fatal 1 "${FUNCNAME[0]}: ${shared_dir} does not exist"
-  fi
+  _require_path "${shared_dir}"
 
   if [[ ! -v tag ]]; then
     _fatal 1 "${FUNCNAME[0]}: missing required '--tag' argument"
diff --git a/vmctl b/vmctl
index 8b6b94f..262f1b5 100755
--- a/vmctl
+++ b/vmctl
@@ -73,11 +73,8 @@ _main() {
         ;;
 
       '-b' | '--basedir' )
-        if [[ ! -d "$2" ]]; then
-          _fatal 1 "invalid base directory '$2'"
-        fi
-
         VMCTL_VMROOT="$2"; shift 2
+        _require_path "${VMCTL_VMROOT}"
         ;;
 
       '-h' | '--help' )