How to use file sharing on your Mac

Apple was the first computer company to make networked file sharing easy. Decades after introducing that feature on the Mac, it’s less important in an era of cloud storage. Unless you’re on a corporate network–and often even so–it’s easier to push files to a central repository by copying them to a folder or volume on your desktop that syncs. Cloud storage also bypasses network configuration issues, like the dread “double NAT,” which can prevent making file-exchange connections over the internet.

Still, it’s frequently helpful to allow access to files stored on your Mac by other computers on a local network. Let’s look at what’s required to set it up.

Enable file sharing

Start with System Preferences > Sharing. This one-stop shop for all networked services that macOS includes a checkbox for File Sharing. Enabling file sharing lets you or anyone with an account on that Mac access the computer’s file server using account credentials and requiring no additional configuration. Anyone with an account with Admin below their account name in Users & Groups can access files across the startup and all mounted volumes. People with regular user accounts can access their home directory and the Home folder’s Shared folder by default.

Apple discontinued its original file-sharing software, AFP (Apple Filing Protocol), in favor of the Microsoft-initiated SMB (Server Message Block). This allows a huge range of devices to connect to a Mac that has file sharing turned on. You can see the history of Apple’s support by selecting File Sharing in the Sharing preference pane and clicking Options. For the last few releases of macOS, only the “Share files and folders using SMB” checkbox appears, an odd choice. But for several years, AFP and SMB were separately selectable before AFP disappeared.

However, this is also where you can enable backward compatibility for Windows systems that use an older version of SMB.

Configure file sharing

You have several options for what you might share and with whom:

• Limit sharing to you and other people with regular and admin accounts on the Mac. That’s the default and requires no further work.
• Create shared folders that people with regular accounts on the Mac can access to create pooled local storage or a write-only drop box. (That’s the lowercase “drop box”: a place to deposit things.)
• Create sharing-only users, who can’t log into a Mac or connect to it via a Terminal session; they can only access shared folders. (See “How to create a sharing-only user in macOS to limit access.”)

Add shared folders by clicking the + (plus) at the bottom of the Shared Folders list. You can select any volume or folder. Remove a folder or volume by selecting it and clicking – (minus).

Assign users and permissions to shared folders by selecting the folder in the Shared Folders list and then modifying existing permissions in the Users list. You can add users groups by clicking +. (You can also remove certain users and groups by selecting one and clicking “-“.)

The permissions next to each user or group entry are the same as found in the Finder:

• Read & Write: All access, including deleting items and adding them.
• Read Only: Retrieve anything in the folder, including nested items.
• Write Only (Drop Box): Allows a user to copy a file to the destination but not view it or any other contents of the folder.
• No Access: Available only for Everyone to disable access to all other users and to guest connections.

If the Guest User in System Preferences > Users & Groups has “Allow guest users to connect to shared folders” checked, guest users can access any shared folder that has Everyone set to a value other than No Access. However, you can also explicitly disable guest access by Control-clicking a shared folder, choosing Advanced Options, and unchecking “Allow guest users.”

You can also use Advanced Options to enable networked Time Machine backups to a particular folder on a volume. I explain that process in “How to set your Mac as a shared backup destination for Time Machine.”

A quick warning! With file sharing active, conceivably anyone anywhere in the world could reach your Mac and act as a guest user or try to log in. On most home networks, ISP and router configuration make it nearly or entirely impossible. Still, I suggest disabling or restricting guest access to avoid sharing anything you didn’t intend to with the world.

Connect to a Mac’s file server

From macOS, you can connect to a file server in the Finder. Open any Finder and look under the Locations list. Macs with file sharing or screen sharing enabled appear there. (If you don’t see them, go to Finder > Preferences > Sidebar and check Bonjour computers.) Click any server and then click Connect As, enter credentials, and select an available volume.

Some servers won’t show up in the Finder, depending on your local network. Click the Network link in the Finder sidebar under Locations or choose Go > Network (Command-Shift-K).

If you need to enter a Mac’s address, choose Go > Connect to Server (Command-K). You enter the address in the format smb://address, such as smb://10.0.1.120, and click Connect or press Return. A Finder window appears, just as if you clicked a server in the Finder sidebar.

For Macs that you can’t see via Bonjour or to connect to a Mac from a Windows computer or other system, you can find the Mac’s address in System Preferences > Network. Select any active interface in the left-hand list, and in the main section of the pane under Connected the IP address will appear.

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