You’ve installed Ollama, you try to run a model, and nothing happens — or you get a cryptic error you’ve never seen before. This is frustrating, but nearly every Ollama startup issue falls into one of a handful of root causes. This guide works through them systematically, from the most common to the more obscure, covering Windows, macOS, and Linux.
Start Here: Check If Ollama Is Actually Running
Before diagnosing anything else, confirm whether the Ollama server process is running at all. Many “Ollama not working” issues turn out to be that the server simply isn’t started.
Windows: Look for the Ollama icon in your system tray (bottom-right, near the clock). If it’s there, Ollama is running. If not, launch it from the Start menu. You can also check from PowerShell:
Get-Process ollamamacOS: Check the menu bar for the Ollama icon. If missing, launch from Applications. From Terminal:
pgrep -x ollamaA process ID returned means it’s running. No output means it’s not.
Linux:
systemctl status ollamaLook for active (running). If you see inactive or failed, that’s your starting point.
Once you know whether the process is running, try a basic connectivity test:
curl http://localhost:11434If Ollama is running and listening, this returns Ollama is running. If it returns “connection refused”, the server isn’t listening on that port — either it’s not running, or it’s bound to a different address.
Port 11434 Is Already in Use
Ollama defaults to port 11434. If something else is already using that port, Ollama fails to start — sometimes silently, sometimes with an “address already in use” error.
Check what’s using the port:
# Windows
netstat -ano | findstr 11434
# macOS / Linux
lsof -i :11434
# or
ss -tlnp | grep 11434If a different process is using 11434, you have two options: kill that process, or change Ollama’s port. To change Ollama’s port, set the OLLAMA_HOST environment variable to a different port:
OLLAMA_HOST=127.0.0.1:11435Then restart Ollama. Any tools connecting to it (Open WebUI, Continue, scripts) will need to be updated to use the new port too.
On Linux, a previously failed Ollama process sometimes leaves a socket file behind that blocks the port. If lsof -i :11434 shows nothing but Ollama still won’t bind to the port, check for and remove stale socket files:
sudo rm -f /tmp/ollama*.sock
sudo systemctl restart ollamaService Failed to Start on Linux
On Linux with systemd, a failed service usually leaves useful diagnostic information in the journal. This is the fastest path to understanding what went wrong:
journalctl -u ollama -n 50 --no-pagerRead through the output carefully. Common things to look for:
“Permission denied” — The ollama user doesn’t have permission to access a file or directory. This often happens when you’ve manually moved model files or changed the models directory without updating ownership. Fix:
sudo chown -R ollama:ollama /usr/share/ollama
sudo chown -R ollama:ollama /your/custom/models/path # if OLLAMA_MODELS is set“Address already in use” — Port conflict, covered above.
“No such file or directory” for the binary — Ollama wasn’t installed correctly or the binary was moved. Reinstall:
curl -fsSL https://ollama.com/install.sh | shCUDA/GPU errors — The service started but couldn’t initialise the GPU. Covered in the GPU section below.
Ollama Crashes Immediately After Starting
If Ollama starts briefly then crashes, the cause is almost always one of: insufficient memory for the model being loaded, a corrupted model file, or a GPU driver issue. Work through these in order:
Check available memory. Run ollama run modelname in a terminal and watch whether it crashes during model loading. If it crashes with an out-of-memory error, you don’t have enough RAM or VRAM for that model. Try a smaller model or a more aggressively quantized version.
Check for corrupted model files. A partial or interrupted download leaves a corrupted model file that causes crashes on load. Delete the model and re-pull it:
ollama rm modelname
ollama pull modelnameIf you’re unsure which model is corrupted, list them with ollama list and try running each one to identify which crashes.
Enable debug logging to see what Ollama is doing right before it crashes:
# Linux / macOS
OLLAMA_DEBUG=1 ollama serve
# Windows PowerShell
$env:OLLAMA_DEBUG=1; ollama serveThe debug output shows exactly what Ollama is loading and where it fails.
Figure 1 — Ollama Startup Issues: Diagnosis Flowchart
GPU Not Detected or CUDA Errors
GPU-related startup failures are among the most common on Windows and Linux. Ollama tries to initialise CUDA on startup — if that fails, it either falls back to CPU silently or, in some configurations, refuses to start entirely.
Signs of GPU initialisation failure: the service starts but ollama ps shows CPU after loading a model, or you see CUDA-related errors in debug output like CUDA library not found or no CUDA devices available.
The fix depends on the error:
CUDA library not found: Ollama bundles its own CUDA runtime, but occasionally the bundled files get corrupted or blocked by antivirus. Reinstall Ollama — this re-downloads and places the CUDA runtime files correctly. On Windows, temporarily disable antivirus during install and add the Ollama directory to your antivirus exclusions list.
Insufficient driver version: Your NVIDIA driver is too old. Download and install the latest driver from nvidia.com — use “Custom” install with “Clean install” checked to remove stale components. After driver update, restart your machine (not just Ollama).
No CUDA devices available: CUDA is installed but can’t see your GPU. This can happen if: another application has exclusive access to the GPU (some virtualisation software does this), you’re running over Remote Desktop (which sometimes disables CUDA), or the GPU has been disabled in Device Manager. Check Device Manager on Windows for any warning signs on your GPU.
Ollama Works Then Stops Responding
If Ollama starts fine but becomes unresponsive after a while — requests time out, the API stops responding — the most common cause is a model that crashed mid-generation and left the server in a bad state.
The fix is simple: restart Ollama. On Linux:
sudo systemctl restart ollamaOn macOS: click the menu bar icon → Quit, then relaunch. On Windows: right-click system tray → Quit, then relaunch.
If this happens repeatedly, watch your system memory during inference. If RAM or swap usage climbs to 100% during model generation, you’re running out of memory — the model is too large for your hardware and the OOM condition crashes the generation thread. Either use a smaller model or reduce the context length (--parameter num_ctx 2048) to reduce memory pressure.
On Linux, you can set up automatic restart on failure in the systemd unit:
sudo systemctl edit ollama[Service]
Restart=always
RestartSec=5This makes systemd restart Ollama automatically if it crashes, which is useful for server setups where you don’t want manual intervention.
Windows-Specific: Ollama Won’t Start After a Windows Update
Windows updates occasionally change system DLL versions or GPU driver state in ways that break Ollama’s startup. If Ollama stopped working after a Windows update, try these in order:
- Quit Ollama from the system tray and relaunch it
- Restart your machine completely (not just sleep/hibernate)
- Update your NVIDIA driver to the latest version
- Reinstall Ollama — download the latest installer from ollama.com and run it
Most Windows-update-related Ollama failures are fixed by one of the first three steps. The driver update is particularly important if Windows Update also updated the GPU driver to a version that’s incompatible with Ollama’s bundled CUDA runtime — fresh NVIDIA driver from nvidia.com is usually more compatible than the version Windows Update installs.
macOS-Specific: Ollama Fails After macOS Update
macOS updates can revoke permissions that Ollama previously had, particularly around network access and background service registration. If Ollama stopped working after a macOS update:
Check System Settings → Privacy & Security → Network to confirm Ollama still has network access permission. If it was reset, re-grant it. If the menu bar app launches but the API doesn’t respond, try quitting completely and relaunching — macOS updates sometimes require a fresh app start to re-register the background service. In persistent cases, uninstalling and reinstalling Ollama (download fresh .dmg from ollama.com) typically resolves any permission or service registration issues from the update.
Figure 2 — Common Ollama Errors: Quick Reference
Checking Logs for Anything Not Covered Here
If you’ve worked through the above and Ollama still won’t start, logs are the next step. They almost always contain the specific error that’s causing the failure.
Linux:
journalctl -u ollama -n 100 --no-pagerWindows: Open Event Viewer (search in Start menu), navigate to Windows Logs → Application, and filter by “ollama” as the source. Errors will appear with timestamps and specific messages.
macOS: Open Console.app (in Applications → Utilities), search for “ollama” in the search bar, and look at log entries around the time it failed to start.
With debug logging enabled (OLLAMA_DEBUG=1), run ollama serve directly in a terminal on all platforms and watch the output live. The combination of the platform’s system logs and Ollama’s own debug output gives you a complete picture of what’s failing and why. For issues not covered here, the Ollama GitHub issues page and the r/LocalLLaMA subreddit are both active and generally surface fixes for platform-specific problems quickly after new Ollama releases.
Posting your log output to the Ollama GitHub discussion board usually gets a response from the maintainers or community within a day or two — they are active and take startup issues seriously, especially if the error is reproducible across multiple users after a new release.
Preventing Issues: Keeping Ollama Healthy Long-Term
A few habits keep Ollama running reliably over time. Keep Ollama updated — most persistent startup issues are fixed in newer releases, and the update is a one-step process on all platforms. Don’t move model files manually outside of Ollama’s model management commands — use ollama rm and ollama pull rather than deleting or copying files directly in the models directory, as manual file operations can leave the model registry in an inconsistent state. If you change the OLLAMA_MODELS path, make sure the ollama system user has ownership of the new directory on Linux. And on Windows, add the Ollama installation directory and models directory to your antivirus exclusion list — overzealous antivirus scanning of large model files is a surprisingly common source of intermittent failures that are difficult to diagnose without knowing to look there.