Enhancing macOS SMB Stability and Usability with Custom Configurations

The Server Message Block (SMB) protocol is essential for file sharing and network communication across various devices. macOS, being widely used in both personal and professional environments, often interacts with SMB servers for tasks such as accessing shared drives or collaborating on networked files. However, macOS’s default SMB implementation may not be optimal for all users, occasionally leading to performance issues, connectivity problems, or unexpected behaviors. Customizing the SMB settings can significantly enhance stability, usability, and compatibility, especially in demanding environments.

This article outlines how to create a custom configuration for SMB on macOS by editing the nsmb.conf file. The provided configuration improves reliability, optimizes performance, and disables unnecessary features.

Editing the nsmb.conf File

The nsmb.conf file is macOS’s configuration file for SMB settings. To edit this file, open a terminal and use a text editor like vim:

sudo vim /etc/nsmb.conf

Below is the detailed configuration and its corresponding explanations:

Custom Configuration

[default]
# Use NTFS streams if supported
streams=yes

# Soft mount by default
soft=yes

# Disable signing due to macOS bug
signing_required=no

# Disable directory caching
dir_cache_max_cnt=0
dir_cache_max=0
dir_cache_off=yes

# Lock negotiation to SMB2/3 only
protocol_vers_map=4

# No SMB1, so we disable NetBIOS
port445=no_netbios
validate_neg_off=yes

# Turn off notifications
notify_off=yes

# SMB Multichannel behavior
mc_on=yes
mc_prefer_wired=yes

Configuration Breakdown

1. Enabling NTFS Streams
   • streams=yes
   • This setting ensures macOS uses NTFS alternate data streams if supported by the server. This is crucial for maintaining metadata and improving compatibility with Windows-based systems.
2. Soft Mounts
   • soft=yes
   • Enabling soft mounts prevents the system from freezing if the SMB server becomes unresponsive. This improves user experience, particularly when working with unstable networks.
3. Disabling Signing
   • signing_required=no
   • Disabling SMB signing resolves a known macOS bug that can slow down file transfers and cause connection drops. However, this should only be done in secure, trusted environments.
4. Disabling Directory Caching
   • dir_cache_max_cnt=0 dir_cache_max=0 dir_cache_off=yes
   • Directory caching can lead to stale data and incorrect directory listings. Disabling this ensures the system fetches the latest directory contents directly from the server.
5. Restricting Protocols
   • protocol_vers_map=4
   • This setting restricts SMB to versions 2 and 3, enhancing security and performance by eliminating the outdated and vulnerable SMB1 protocol.
6. Disabling NetBIOS
   • port445=no_netbios validate_neg_off=yes
   • NetBIOS is unnecessary when SMB1 is disabled. Turning it off improves security and prevents port conflicts.
7. Disabling Notifications
   • notify_off=yes
   • Disabling SMB notifications minimizes resource usage and prevents unwanted pop-ups.
8. Optimizing SMB Multichannel
   • mc_on=yes mc_prefer_wired=yes
   • Enabling SMB multichannel increases throughput by leveraging multiple network connections. Prioritizing wired connections ensures stability in environments where both Wi-Fi and Ethernet are available.

Applying Changes

After saving the configuration file, restart your SMB services to apply the changes. Since macOS doesn’t provide a direct way to restart SMB, you can either log out and log back in or restart your computer.

Benefits of Customizing SMB

• Increased Stability: Avoiding crashes or freezes with soft mounts and reduced caching.
• Enhanced Performance: Faster file transfers by disabling unnecessary features and optimizing the protocol.
• Improved Security: Eliminating SMB1 and NetBIOS reduces vulnerabilities.
• Better Resource Utilization: Disabling notifications and unnecessary caching conserves system resources.

Final Thoughts

Customizing the SMB settings in macOS can drastically improve its reliability and usability in networked environments. While the default settings may suffice for casual users, advanced configurations like the one presented here are invaluable for professionals and power users. Before implementing these changes, ensure they align with your specific network environment and security policies.