caddyserver/caddy · error

syncing downloaded file to device: %v

Error message

syncing downloaded file to device: %v

What it means

After the bytes are written, destFile.Sync() (fsync) fails, meaning the OS could not flush the downloaded binary to stable storage. This signals hardware/filesystem trouble: I/O errors, device full, or the file living on failing storage. The deferred restore brings back the original binary.

Source

Thrown at cmd/packagesfuncs.go:336

func writeCaddyBinary(path string, body *io.ReadCloser, fileInfo os.FileInfo) error {
	l := caddy.Log()
	destFile, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, fileInfo.Mode())
	if err != nil {
		return fmt.Errorf("unable to open destination file: %v", err)
	}
	defer destFile.Close()

	l.Info("downloading binary", zap.String("destination", path))

	_, err = io.Copy(destFile, *body)
	if err != nil {
		return fmt.Errorf("unable to download file: %v", err)
	}

	err = destFile.Sync()
	if err != nil {
		return fmt.Errorf("syncing downloaded file to device: %v", err)
	}

	return nil
}

const downloadPath = "https://caddyserver.com/api/download"

type pluginPackage struct {
	Version string
	Path    string
}

func (p pluginPackage) String() string {
	if p.Version == "" {
		return p.Path
	}
	return p.Path + "@" + p.Version
}

View on GitHub (pinned to 50e54ee279)

Solutions

1. Check disk health and space: df -h on the binary's mount, dmesg | grep -i 'i/o error'
2. Free space and retry the upgrade
3. If storage is genuinely failing, replace it before attempting any upgrade
4. Move the binary to reliable local storage and re-run

df -h "$(dirname "$(command -v caddy)")"   # confirm free space before upgrading

When it happens

Trigger: Disk full exactly at fsync time; failing disk or NFS mount erroring on flush; loop-device/container overlay issues; USB media removed.

Common situations: Small root partitions filling during the ~40MB write; flaky network-attached storage holding /usr/local/bin; failing SSD returning EIO.

Related errors

• retrieving current executable permission bits: %v
• resolving current executable symlink: %v
• backing up current binary: %v
• unable to open destination file: %v
• checking if default Caddyfile exists: %v

AI-assisted analysis of caddyserver/caddy@50e54ee279 (2026-08-15). Data as JSON: /api/errors/dc96e7b137a767cc. Report an issue: GitHub.