Many corporate environments use NTLM-authenticated proxies for security, which creates headaches for developers trying to use package managers like apt-get. Unlike basic auth proxies, NTLM requires a more complex authentication handshake that apt-get doesn't natively support.

Before proceeding, ensure you have:

• Administrative access to your Ubuntu system
• Valid proxy credentials (domain\username format)
• Proxy server address and port
• Python installed (usually comes pre-installed)

The most reliable approach is to use CNTLM (a proxy that handles NTLM authentication) as an intermediate between apt-get and your corporate proxy. Here's how to set it up:

sudo apt-get install cntlm

After installation, configure CNTLM:

sudo nano /etc/cntlm.conf

Add your proxy details (example configuration):

Username    your_username
Domain      your_domain
Password    your_password
Proxy       proxy.corporate.com:8080
Listen      3128

Then restart CNTLM:

sudo service cntlm restart

Now configure apt to use your local CNTLM proxy:

sudo nano /etc/apt/apt.conf.d/proxy.conf

Add these lines:

Acquire::http::Proxy "http://127.0.0.1:3128";
Acquire::https::Proxy "http://127.0.0.1:3128";

If CNTLM doesn't work for your environment, try ntlmaps:

sudo apt-get install python
wget https://sourceforge.net/projects/ntlmaps/files/ntlmaps-0.9.9.0.1.tar.gz
tar -xzvf ntlmaps-0.9.9.0.1.tar.gz
cd ntlmaps-0.9.9.0.1

Edit server.cfg:

[Main]
ListenPort: 5865
ParentProxy: your.proxy.com:8080
ParentAuth: NTLM

Verify everything works by running:

sudo apt-get update

If you encounter errors, check CNTLM's logs:

tail -f /var/log/cntlm.log

To ensure your proxy settings survive reboots:

sudo systemctl enable cntlm

Or for older systems:

sudo update-rc.d cntlm defaults

If authentication fails:

• Verify your password hasn't expired
• Check if your domain format is correct (DOMAIN\user)
• Test your credentials with cntlm -u your_username -d your_domain -H
• Ensure no firewall is blocking port 3128

---

Many corporate environments enforce NTLM authentication for proxy servers, which creates headaches when trying to use Ubuntu's package management system. Unlike basic authentication, NTLM requires special handling that apt-get doesn't support natively.

The standard proxy configuration in /etc/apt/apt.conf using:

Acquire::http::Proxy "http://user:pass@proxy:port";

only works for basic authentication. NTLM requires multiple message exchanges that standard HTTP proxy connections don't handle.

The most reliable approach is to use CNTLM (Connection NTLM) as a local proxy that handles the NTLM authentication while presenting a standard proxy interface to apt-get.

Install CNTLM:

sudo apt-get install cntlm

Edit the configuration file at /etc/cntlm.conf:

Username    your_username
Domain      your_domain
Password    your_password
Proxy       your.proxy.address:port
NoProxy     localhost, 127.0.0.*, 10.*, 192.168.*
Listen      127.0.0.1:3128

Generate the NTLM password hashes:

sudo cntlm -H -d your_domain -u your_username

This will output hashes you should add to the config file, then replace the plaintext password with these hashes for security.

Configure apt to use the local CNTLM proxy by editing /etc/apt/apt.conf:

Acquire::http::Proxy "http://127.0.0.1:3128";
Acquire::https::Proxy "http://127.0.0.1:3128";

For temporary solutions, you can create a tunnel with ncat:

ncat --proxy-type http --proxy-auth user:pass --proxy proxy:port -l 3128

Then point apt-get to localhost:3128 as above.

If you get authentication failures:

1. Verify your domain is correctly specified
2. Check if your password has special characters that need escaping
3. Try using the NTLMv2 hashes instead of NTLMv1

For performance issues, try adjusting the CNTLM packet size settings in the config file.

Always:

• Use hashed passwords in CNTLM config
• Restrict CNTLM to listen only on localhost
• Regularly update your package lists to detect any MITM attacks