ensure executable paths are absolute

systemdspawner/systemd.py

@@ -9,6 +9,7 @@
 import os
 import re
 import shlex
+import shutil
 import subprocess
 import warnings
 
@@ -143,6 +144,24 @@ async def start_transient_service(
         )
         run_cmd.append(f"--property=EnvironmentFile={environment_file}")
 
+    # make sure cmd[0] is absolute, taking $PATH into account.
+    # systemd-run does not use the unit's $PATH environment
+    # to resolve relative paths.
+    if not os.path.isabs(cmd[0]):
+        if environment_variables and "PATH" in environment_variables:
+            # if unit specifies a $PATH, use it
+            path = environment_variables["PATH"]
+        else:
+            # search current process $PATH by default.
+            # this is the default behavior of shutil.which(path=None)
+            # but we still need the value for the error message
+            path = os.getenv("PATH", os.defpath)
+        exe = cmd[0]
+        abs_exe = shutil.which(exe, path=path)
+        if not abs_exe:
+            raise FileNotFoundError(f"{exe} not found on {path}")
+        cmd[0] = abs_exe
+
     # Append typical Spawner "cmd" and "args" on how to start the user server
     run_cmd += cmd + args
 

tests/test_systemd.py

@@ -126,6 +126,26 @@ async def test_workdir():
             assert text == d
 
 
+async def test_executable_path():
+    unit_name = "systemdspawner-unittest-" + str(time.time())
+    _, env_filename = tempfile.mkstemp()
+    with tempfile.TemporaryDirectory() as d:
+        await systemd.start_transient_service(
+            unit_name,
+            ["bash"],
+            ["-c", f"pwd > {d}/pwd"],
+            working_dir=d,
+            environment_variables={"PATH": os.environ["PATH"]},
+        )
+
+        # Wait a tiny bit for the systemd unit to complete running
+        await asyncio.sleep(0.1)
+
+        with open(os.path.join(d, "pwd")) as f:
+            text = f.read().strip()
+            assert text == d
+
+
 async def test_slice():
     unit_name = "systemdspawner-unittest-" + str(time.time())
     _, env_filename = tempfile.mkstemp()