Error Code Encyclopedia
What an error actually means, why it happens, and how to fix it — for Cloudflare edge errors, Windows update codes, Git, Docker, Kubernetes, and DNS.
Looking for standard HTTP status codes (404, 500, etc.)? See the HTTP Status Codes reference.
Cloudflare
Cloudflare-specific edge error codes (520-530 range) — distinct from standard HTTP status codes.
Web Server Returns an Unknown Error
Cloudflare received an empty, reset, or otherwise unparseable response from your origin server.
Web Server Is Down
Cloudflare cannot establish a connection to your origin server at all — it's actively refusing connections.
Connection Timed Out
Cloudflare's connection attempt to your origin server timed out — the server is reachable at the network level but not responding in time.
SSL Handshake Failed
Cloudflare could not complete an SSL/TLS handshake with your origin server.
Invalid SSL Certificate
Cloudflare completed the SSL handshake but the origin's certificate failed validation under "Full (strict)" mode.
Windows
Windows Update and system error codes (0x8007xxxx format).
Access Denied
A permissions error — Windows denied access to a file, registry key, or service needed to complete the operation.
Out of Memory or System Resources
Windows Update (or another operation) ran out of memory or system resources mid-process.
Update Installation Failed
A generic Windows Update or MSI installer failure, most commonly tied to .NET Framework updates.
The System Cannot Find the File Specified
Windows Update (or another process) couldn't find a file it expected to exist.
Git
Common Git errors when cloning, pushing, and merging.
Permission denied (publickey)
The remote Git server (GitHub, GitLab, etc.) rejected your SSH key — either none was offered, or the one offered isn't authorized.
refusing to merge unrelated histories
Git detected two branches with no common commit ancestor and, by default, refuses to merge them without explicit confirmation.
failed to push some refs (non-fast-forward)
The remote branch has commits your local branch doesn't have — Git refuses to push until you incorporate them first.
You Are in "Detached HEAD" State
You've checked out a specific commit directly instead of a branch — new commits here won't belong to any branch unless you create one.
Docker
Docker daemon, port, and storage errors.
Cannot Connect to the Docker Daemon
The docker CLI can't reach the Docker daemon (dockerd) — usually because it isn't running, or your user lacks permission to access its socket.
Port Is Already Allocated
A container failed to start because the host port you're trying to map is already in use by another process or container.
No Space Left on Device
Docker has run out of disk space — usually from accumulated unused images, stopped containers, and build cache, not the disk itself being full.
Kubernetes
Pod scheduling and container startup failures.
CrashLoopBackOff
A container in the pod is starting, crashing, and being restarted repeatedly, with Kubernetes applying an increasing delay between attempts.
ImagePullBackOff
Kubernetes cannot pull the container image specified in the pod spec — usually a wrong image name/tag, or missing registry credentials.
Kubernetes Pod Stuck in Pending State
The pod has been accepted by the cluster but the scheduler can't find a node with enough resources (or matching constraints) to place it on.
DNS
DNS resolution failure response codes.
NXDOMAIN (Non-Existent Domain)
The DNS server successfully responded, but confirmed the requested domain name does not exist in DNS at all.
SERVFAIL
The DNS server encountered an internal error and could not process the query — distinct from NXDOMAIN, which is a definitive "doesn't exist" answer.