Nearby devices

What is smbd?

smbd is the file server behind File Sharing. When another Mac or a Windows PC opens a shared folder on this Mac, the files go through smbd.

Process: smbdMade by AppleApplies to: macOS 14 Sonoma and later. Checked on macOS 27.2.Checked: 1 November 2026

Short answer

Part of macOS. It is the SMB file server for File Sharing, so its traffic is other computers reading and writing this Mac's shared folders.

Safe to block

Safe to block if no other computer needs this Mac's files. It's cleaner to turn off File Sharing in Sharing settings.

Path: /usr/sbin/smbd
launchd label: com.apple.smbd
Signing identifier: com.apple.smbd

What it is

The man page calls smbd the “SMB server daemon”. It services SMB requests from client computers, and launchd normally starts it on port 445.

The program is /usr/sbin/smbd. launchd starts it for the system as com.apple.smbd.

Apple lists TCP port 445 for Microsoft SMB and TCP port 139 for SMB file sharing and Windows print services.

Apple's File Sharing article says that the Public folder of each user is shared automatically when File Sharing is on.

Why it uses the network

Other computers open shared files. Reading a file from this Mac sends it over the network. Writing to a shared folder sends data to this Mac.
Backups and syncs to this Mac. If another computer backs up to a shared folder here, every backup goes through smbd.

How much is normal

With nobody connected, it is quiet.

During a copy, it moves as much as the files you copy, which can be a lot. That traffic stays on your local network unless the other computer is far away.

If you didn't turn on File Sharing, a management profile from your organization may have. Ask your administrator.

When it uses a lot, and why

A large copy. Copying a video library or a project folder from this Mac moves every byte over the network.
Backups to this Mac. Another computer that backs up to a shared folder here can write large amounts, especially the first time.
An app working on shared files. A media or design app on another computer can read big files from this Mac again and again.

Is it safe to block?

Safe to block

Safe to block if no other computer needs this Mac's files. It's cleaner to turn off File Sharing in Sharing settings.

What breaks if you block it

Other Macs and PCs can't open this Mac's shared folders.
Backups that other computers make to a shared folder here stop.

Blocking means a firewall rule that refuses its connections. Don’t quit or disable a macOS process to save data: macOS starts it again, and other features depend on it.

Reduce its use

Choose Apple menu › System Settings › General › Sharing.
Turn off File Sharing if you don't use it.
If you need it, share only the folders you need. Select a folder in the Shared Folders list and click the remove button.
In the folder's Advanced Options, turn on “Only allow SMB encrypted connections” if you share over untrusted networks.
Don't quit smbd while someone copies files. Their copy fails.

See how much it uses

Open Activity Monitor from Applications › Utilities. Click Network, then search for smbd.
In Terminal, list the computers connected now. Connections to port 445 are SMB clients.
```
sudo lsof -nP -i :445
```
Needs an administrator password.

With Kilobat

In the Kilobat app list, search for smbd. Its row shows the live rate and what it moved today.
In Connections, click the ⓘ button on one of its rows. The popover shows this page’s short answer, without going online.
In Terminal, ask the same question. Add --json for scripts and agents.
```
kilobat explain 'smbd'
```
Show its traffic over one day.
```
kilobat bandwidth 'smbd' day
```
Through MCP, an AI agent asks explain_connection with the process name. It gets the same facts.

The live view and the explanations are free. History in the app needs Kilobat Pro. Blocking needs Pro and the network filter: see the network filter, Protection and the hotspot data saver.

Questions

Does File Sharing use internet data?

Only if the other computer reaches this Mac over the internet. Between computers on your local network, it stays local.

Why is my Public folder shared?

Apple says that the Public folder of each user is shared automatically. Remove it from the Shared Folders list to stop that.

Sources

smbd(8), man page installed with macOS 27.2
launchd property list com.apple.smbd, macOS 27.2
Apple Support: Set up file sharing on Mac
Apple Support: TCP and UDP ports used by Apple software products

Checked on 1 November 2026.