--- title: "smbd: what it is, why it uses so much data, and whether to block it · Kilobat" url: "https://kilobat.app/processes/smbd" description: "smbd is the SMB file server of macOS File Sharing. Why it moves a lot of data, what is normal, and what breaks if you block it." --- 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: `smbd` · Made by Apple · Applies 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 1. Choose Apple menu › System Settings › General › Sharing. 2. Turn off File Sharing if you don't use it. 3. If you need it, share only the folders you need. Select a folder in the Shared Folders list and click the remove button. 4. In the folder's Advanced Options, turn on “Only allow SMB encrypted connections” if you share over untrusted networks. 5. Don't quit `smbd` while someone copies files. Their copy fails. ## See how much it uses 1. Open Activity Monitor from Applications › Utilities. Click Network, then search for `smbd`. 2. 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 1. In the Kilobat app list, search for `smbd`. Its row shows the live rate and what it moved today. 2. In Connections, click the ⓘ button on one of its rows. The popover shows this page’s short answer, without going online. 3. In Terminal, ask the same question. Add `--json` for scripts and agents. ``` kilobat explain 'smbd' ``` 4. Show its traffic over one day. ``` kilobat bandwidth 'smbd' day ``` 5. 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](https://kilobat.app/docs/blocking#filtering), [Protection](https://kilobat.app/docs/blocking#protection) and the [hotspot data saver](https://kilobat.app/save-hotspot-data). ## 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](https://support.apple.com/guide/mac-help/set-up-file-sharing-on-mac-mh17131/mac) - [Apple Support: TCP and UDP ports used by Apple software products](https://support.apple.com/en-us/103229) Checked on 1 November 2026. ## Related - [netbiosd](https://kilobat.app/processes/netbiosd): Part of macOS. It registers and browses NetBIOS names for Windows-style file sharing. Its traffic stays on the local network. - [screensharingd](https://kilobat.app/processes/screensharingd): Part of macOS. It accepts Screen Sharing and VNC connections from other computers, so another person can see and control this Mac. - [sshd](https://kilobat.app/processes/sshd): Part of macOS. It is the SSH server for Remote Login, so other computers can log in to this Mac with SSH or copy files with SFTP. - [The macOS firewall blocks incoming connections](https://kilobat.app/guides/macos-firewall-incoming)