Permission Denied in Temp folder on Windows

[pro-jasonnagy]

I have a flow from my prefect server on Ubuntu and I am trying to get a Windows worker to do runs however I am getting an error saying that access is denied:

14:53:59.053 | ERROR | Flow run 'rough-macaw' - [WinError 5] Access is denied: 'C:\\Users\\jason.nagy\\AppData\\Local\\Temp\\18\\tmp0_x4yprdprefect\\prefect-workflows-test\\.git\\objects\\pack\\pack-b8233f81476ede7f07c417aa498194b26da1266b.idx'

I checked the folder and my user has full permissions so Im not sure why it is complaining I dont have permissions. I confirmed all my prefect versions are up to date. I am using Git submodules and made sure my Github token is valid for all repos needed. The token is set up on my server hosting the deploymen. The worker just has a basic profile to access the server and is then started with prefect worker start --pool "local-pool".

A longer snippet of the logs is pasted below:

14:53:44.989 | INFO    | Flow run 'rough-macaw' - Running 1 deployment pull step(s)
14:53:45.054 | INFO    | Flow run 'rough-macaw' - Executing deployment step: git_clone
14:53:47.798 | DEBUG   | prefect.client - Connecting to API at http://192.168.71.26:4200/api/
14:53:47.823 | DEBUG   | prefect.client - Connecting to API at http://192.168.71.26:4200/api/
14:53:50.359 | DEBUG   | prefect.client - Connecting to API at http://192.168.71.26:4200/api/
14:53:50.366 | DEBUG   | prefect.runner.storage.git-repository.prefect-workflows-test - Pulling contents from repository 'prefect-workflows-test' to 'C:\Users\jason.nagy\AppData\Local\Temp\18\tmp0_x4yprdprefect\prefect-workflows-test'...
14:53:50.366 | DEBUG   | prefect.runner.storage.git-repository.prefect-workflows-test - Cloning repository https://github.com/profinancialca/prefect-workflows.git
14:53:51.183 | DEBUG   | prefect.utilities.services.critical_service_loop - Starting run of 'get_and_submit_flow_runs'
14:53:51.184 | DEBUG   | prefect.workers.process.processworker 5fd8ab9c-f5f7-41bb-86a9-05909f32b3dd - Querying for flow runs scheduled before 2026-05-20 21:54:01.184612+00:00
14:53:51.207 | DEBUG   | prefect.workers.process.processworker 5fd8ab9c-f5f7-41bb-86a9-05909f32b3dd - Discovered 0 scheduled_flow_runs
14:53:54.045 | DEBUG   | prefect.runner.storage.git-repository.prefect-workflows-test - Pulling contents from repository 'prefect-workflows-test' to 'C:\Users\jason.nagy\AppData\Local\Temp\18\tmp0_x4yprdprefect\prefect-workflows-test'...
14:53:54.076 | DEBUG   | prefect.runner.storage.git-repository.prefect-workflows-test - Pulling latest changes from origin/test
14:53:56.463 | ERROR   | prefect.runner.storage.git-repository.prefect-workflows-test - Failed to pull latest changes with exit code Command '['git', '-c', 'url.https://github_pat_********************@github.com.insteadOf=https://github.com', 'pull', 'origin', 'test', '--recurse-submodules', '--depth', '1']' returned non-zero exit status 1.
14:53:59.037 | DEBUG   | prefect.events.clients - Reconnecting websocket connection.
14:53:59.038 | DEBUG   | prefect.events.clients - Opening websocket connection.
14:53:59.041 | DEBUG   | prefect.events.clients - Pinging to ensure websocket connected.
14:53:59.043 | DEBUG   | prefect.events.clients - Pong received. Websocket connected.
14:53:59.043 | DEBUG   | prefect.events.clients - Authenticating...
14:53:59.045 | DEBUG   | prefect.events.clients - Auth result: {'type': 'auth_success'}
14:53:59.045 | DEBUG   | prefect.events.clients - Resending 0 unconfirmed events.
14:53:59.046 | DEBUG   | prefect.events.clients - Finished resending unconfirmed events.
14:53:59.048 | DEBUG   | prefect.events.clients - EventsClient(id=1915758782384): Emitting event id=019e4761-9908-72aa-a68e-541fdb1b4145.
14:53:59.049 | DEBUG   | prefect.events.clients - Added event id=019e4761-9908-72aa-a68e-541fdb1b4145 to unconfirmed events list. There are now 1 unconfirmed events.
14:53:59.049 | DEBUG   | prefect.events.clients - EventsClient(id=1915758782384): Emit reconnection attempt 0.
14:53:59.050 | DEBUG   | prefect.events.clients - EventsClient(id=1915758782384): Sending event id=019e4761-9908-72aa-a68e-541fdb1b4145.
14:53:59.050 | DEBUG   | prefect.events.clients - EventsClient(id=1915758782384): Checkpointing event id=019e4761-9908-72aa-a68e-541fdb1b4145.
14:53:59.051 | DEBUG   | prefect.events.clients - Pinging to checkpoint unconfirmed events.
14:53:59.052 | DEBUG   | prefect.events.clients - EventsClient(id=1915758782384): Pong received. Events checkpointed.
**14:53:59.053 | ERROR   | Flow run 'rough-macaw' - [WinError 5] Access is denied: 'C:\\Users\\jason.nagy\\AppData\\Local\\Temp\\18\\tmp0_x4yprdprefect\\prefect-workflows-test\\.git\\objects\\pack\\pack-b8233f81476ede7f07c417aa498194b26da1266b.idx'**
14:53:59.054 | ERROR   | Flow run 'rough-macaw' - Unexpected exception encountered when trying to load flow
Traceback (most recent call last):
  File "C:\Users\jason.nagy\.conda\envs\prefect\Lib\site-packages\prefect\runner\storage.py", line 446, in _pull_code_locked
    await run_process(cmd, cwd=self.destination)
  File "C:\Users\jason.nagy\.conda\envs\prefect\Lib\site-packages\anyio\_core\_subprocesses.py", line 123, in run_process
    raise CalledProcessError(cast(int, process.returncode), command, output, errors)
subprocess.CalledProcessError: Command '['git', '-c', 'url.https://github_pat_***********@github.com.insteadOf=https://github.com', 'pull', 'origin', 'test', '--recurse-submodules', '--depth', '1']' returned non-zero exit status 1.

[harshagarwalnyu]

This is a Windows UAC/permissions issue with how Prefect tries to write to %TEMP%. A few root causes and fixes:

Most common cause: temp directory path with spaces or special characters

Prefect's subprocess workers sometimes fail when %TEMP% resolves to a path like C:\Users\Your Name\AppData\Local\Temp (space in username). Fix:

# Set TEMP to a path with no spaces before running Prefect
$env:TEMP = "C:\Temp"
$env:TMP = "C:\Temp"
New-Item -ItemType Directory -Force "C:\Temp"
prefect server start

Running as non-admin with restricted temp access

If you're running Prefect as a service account or in a context where %TEMP% is restricted:

# prefect.yaml or in your flow
import tempfile
import os

# Point Prefect to a writable location
os.environ["PREFECT_HOME"] = "C:/PrefectData"
os.environ["TMPDIR"] = "C:/PrefectData/tmp"

Or configure in ~/.prefect/prefect.toml:

[home]
path = "C:/PrefectData"

Antivirus/EDR blocking temp writes

Windows Defender and most EDR solutions scan and sometimes temporarily lock files being written to %TEMP%. This causes transient PermissionError during flow run artifact creation. Fix: add %TEMP%\prefect* and %TEMP%\orion* to your AV exclusions list.

Docker Desktop / WSL2 interaction

If running Prefect inside WSL2 but storing state on the Windows filesystem (/mnt/c/...), temp writes cross the WSL/Windows boundary and can hit permission errors. Keep all Prefect paths inside WSL: use /tmp/prefect or ~/prefect-home instead of Windows paths.

Diagnostic: check the exact error path

import tempfile
print(tempfile.gettempdir())  # see what Prefect will use
# Test write
with tempfile.NamedTemporaryFile(dir=tempfile.gettempdir(), delete=True) as f:
    f.write(b"test")
print("Temp write OK")

If this fails, the temp directory itself is the problem. If it succeeds, the issue is specific to how Prefect is launched (service account vs. user context).