gaierror: [Errno 8] Nodename Nor Servname Provided On macOS Sierra

The error you’re seeing means that the host (domain name or IP address) you are trying to connect to cannot be resolved by the DNS resolver on your machine.

socket.gaierror: [Errno 8] nodename nor servname provided, or not known

Why This Happens

This error generally occurs in Python when you’re trying to make a network request using a bad or undefined hostname:

Common Causes:

1. Typo in the hostname or URL

socket.gethostbyname("example.com")  # typo: 'htp' instead of 'http'

2. Host is empty or None

socket.gethostbyname("")  # Empty host string

3. Network issues or no internet connection

4. Trying to resolve a private/local hostname that doesn’t exist

5. Invalid port or malformed address

6. Improper proxy setup

How to Fix It

1. Check the host string
Make sure you are passing a valid and correctly spelled hostname, e.g.:

socket.gethostbyname("google.com")  # ✅

2. Avoid passing None or empty string
Ensure variables aren’t empty:

host = "example.com"
if host:
    socket.gethostbyname(host)
else:
    print("Invalid host")

3. Debug with print()
If you’re using requests or a library:

print("Connecting to:", url)  # Make sure it's valid

4. Check your internet connection
Try ping google.com in your terminal to verify DNS is working.

5. If you’re using requests or urllib

Bad:

requests.get(some-host")  # typo or non-existent host

Fix:

requests.get("example.com")

Example Fix

Before (may cause the error):

host = ""
socket.gethostbyname(host)

After (safe usage):

import socket
try:
    ip = socket.gethostbyname("example.com")
    print("IP Address:", ip)
except socket.gaierror as e:
    print("Hostname resolution failed:", e)

You’re encountering a known issue with socket.gethostbyname(socket.gethostname()) on macOS Sierra and later. Here’s what’s happening:

Why It Worked on El Capitan (but not Sierra+)

• On OS X El Capitan, socket.gethostname() typically returned a resolvable hostname (one that DNS could map to an IP address).
• On macOS Sierra and later, socket.gethostname() often returns a local name that’s not resolvable (like MacBook-Pro.local or something without a DNS entry), causing socket.gethostbyname() to fail with:

gaierror: [Errno 8] nodename nor servname provided, or not known

Best Cross-Platform Alternative

If you’re trying to get your local IP address, use this method instead:

import socket
def get_local_ip():
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    try:
        # Doesn't even need to be reachable
        s.connect(("8.8.8.8", 80))
        ip = s.getsockname()[0]
    except Exception:
        ip = "127.0.0.1"
    finally:
        s.close()
    return ip
print(get_local_ip())

Output:

Returns your actual local IP address, like:

192.168.1.12

This method:

• Works across all modern macOS versions
• Doesn’t depend on DNS or local hostname resolution
• Is fast and reliable

Optional Fix: Edit /etc/hosts (Not Recommended)

You could manually add a line to /etc/hosts like:

127.0.0.1   MacBook-Pro.local

but this is not recommended, as it’s brittle and can break networking.

Also Read:

Node JS Multer