Safeguard for noexec

We may have users that run into problems with our current
payload model, so this gives us an escape valve.

docs/troubleshooting.md

@@ -76,3 +76,10 @@ install script which version to install.
 ```sh
 curl -fsSL https://ollama.com/install.sh | OLLAMA_VERSION="0.1.29" sh
 ```
+
+## Linux tmp noexec 
+
+If your system is configured with the "noexec" flag where Ollama stores its
+temporary executable files, you can specify an alternate location by setting
+OLLAMA_TMPDIR to a location writable by the user ollama runs as.  For example
+OLLAMA_TMPDIR=/usr/share/ollama/

gpu/assets.go

@@ -22,11 +22,20 @@ var (
 func PayloadsDir() (string, error) {
 	lock.Lock()
 	defer lock.Unlock()
+	var err error
 	if payloadsDir == "" {
 		cleanupTmpDirs()
-		tmpDir, err := os.MkdirTemp("", "ollama")
-		if err != nil {
-			return "", fmt.Errorf("failed to generate tmp dir: %w", err)
+		tmpDir := os.Getenv("OLLAMA_TMPDIR")
+		if tmpDir == "" {
+			tmpDir, err = os.MkdirTemp("", "ollama")
+			if err != nil {
+				return "", fmt.Errorf("failed to generate tmp dir: %w", err)
+			}
+		} else {
+			err = os.MkdirAll(tmpDir, 0755)
+			if err != nil {
+				return "", fmt.Errorf("failed to generate tmp dir %s: %w", tmpDir, err)
+			}
 		}
 
 		// Track our pid so we can clean up orphaned tmpdirs