exportfs Command: Tutorial & Examples

The exportfs command is a powerful utility in Linux used to maintain the current table of exported file systems for NFS (Network File System). This command allows you to export directories to remote users, granting them access over the network. With exportfs, you can manage which directories are available to which clients and with what permissions.

How It Works

exportfs works by manipulating the /var/lib/nfs/etab file, which keeps track of the exported file systems. When you use exportfs to export directories, it updates this file to reflect the current state of exports. The NFS Kernel server then reads this information to determine which directories are accessible to remote clients.

The command interacts closely with the /etc/exports file, which contains a list of directories to be shared and the permissions associated with them. When exportfs is run, it reads this file to determine the list of directories to export.

What It Is Used For

exportfs is primarily used to:

• Export directories to specific clients or networks.
• Unexport directories that were previously exported.
• Display the current list of exported directories.
• Refresh the list of exported directories to apply changes made in the /etc/exports file.

Why It Is Important

The exportfs command is vital for administrators who need to manage shared resources in a networked environment. By allowing precise control over which directories are shared and the permissions granted to each client, exportfs plays a critical role in ensuring both accessibility and security.

How to Use It and Common Command Line Parameters

Here are some common uses and parameters of the exportfs command:

Display Current Exports

To display the current list of exported directories, use:

exportfs -v

Export All Directories

To export all directories listed in the /etc/exports file, use:

exportfs -a

Unexport All Directories

To unexport all currently exported directories, use:

exportfs -u -a

Export a Specific Directory

To export a specific directory (e.g., /srv/nfs), use:

exportfs -o rw,sync,no_subtree_check client_ip:/srv/nfs

Here, the -o flag specifies the options for the export. Common options include:

• rw: Read-write access.
• ro: Read-only access.
• sync: Replies to requests only after changes have been committed to stable storage.
• no_subtree_check: Disables subtree checking, improving performance.

Refresh Exports

To re-read the /etc/exports file and apply any changes, use:

exportfs -r

Potential Problems and Pitfalls

While using exportfs, you might encounter some common issues:

Permissions Errors

If you don't have the necessary permissions to execute the command, you might see errors like:

exportfs: /mnt/nfs: Function not implemented

Make sure you run the command as the root user or with sudo.

Configuration Errors in /etc/exports

Errors in the /etc/exports file can prevent directories from being exported. A common mistake is incorrect syntax or missing options. Always double-check your /etc/exports file for errors:

/srv/nfs    client_ip(rw,sync,no_subtree_check)

Network Issues

If clients can't access the exported directories, you might be facing a network issue. Ensure that both the server and clients are properly connected and that firewalls are configured to allow NFS traffic.

Typical Output

When you run exportfs -v, you might see output like:

/srv/nfs   client_ip(rw,sync,wdelay,hide,no_subtree_check,insecure,root_squash,no_all_squash)

This output lists the exported directory, the client IP, and the options associated with the export.

Examples

Here are some practical examples of using exportfs in a shell:

Example 1: Exporting a Directory

sudo exportfs -o rw,sync,no_subtree_check 192.168.1.100:/srv/nfs

This command exports the /srv/nfs directory to the client with IP 192.168.1.100 with read-write access.

Example 2: Unexporting a Directory

sudo exportfs -u 192.168.1.100:/srv/nfs

This command unexports the /srv/nfs directory for the specified client.

Example 3: Refreshing Exports

sudo exportfs -r

This command re-reads the /etc/exports file and applies any changes.

Example 4: Displaying Current Exports

sudo exportfs -v

Displays the list of currently exported directories along with their options.

Conclusion

The exportfs command is an essential tool for managing NFS exports in a Linux environment. By understanding how to use it effectively, you can ensure that your network shares are configured correctly and securely. Whether you're exporting directories, unexporting them, or simply checking the current state of exports, exportfs provides the functionality you need to manage your NFS server efficiently.