exportfs

The exportfs command is used to maintain the NFS table of exported file systems. It is a crucial tool for managing NFS shares defined in the /etc/exports file. This guide explains the usage of exportfs, including its options and typical use cases.

Usage

exportfs [options] [client:/directory ...]

Common Options

• -a: Export or unexport all directories listed in /etc/exports.

• -r: Reexport all directories. This is useful after modifying /etc/exports.

• -u: Unexport one or more directories.

• -v: Verbose output. Useful for debugging and seeing detailed information.

• -o: Specify export options (overrides /etc/exports).

Examples

Export All NFS Shares

To export all directories listed in /etc/exports:

sudo exportfs -a

Reexport All NFS Shares

To reexport all directories (e.g., after modifying /etc/exports):

sudo exportfs -r

Unexport All NFS Shares

To unexport all directories listed in /etc/exports:

sudo exportfs -ua

Export a Specific Directory

To export a specific directory to a specific client:

sudo exportfs client:/directory

Example:

sudo exportfs 192.168.1.100:/srv/nfs

Unexport a Specific Directory

To unexport a specific directory:

sudo exportfs -u client:/directory

Example:

sudo exportfs -u 192.168.1.100:/srv/nfs

Export with Specific Options

To export a directory with specific options (overriding /etc/exports):

sudo exportfs -o rw,sync,no_subtree_check client:/directory

Example:

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

Display Currently Exported File Systems

To see the list of currently exported file systems:

sudo exportfs -v

Practical Use Cases

Adding a New Export

1. Edit /etc/exports:

   sudo nano /etc/exports

   Add a line for the new export:

   /new/export 192.168.1.0/24(rw,sync,no_subtree_check)

2. Reexport NFS Shares:

   sudo exportfs -r

Temporarily Export a Directory

To temporarily export a directory without modifying /etc/exports:

sudo exportfs -o rw,sync,no_subtree_check 192.168.1.100:/temporary/export

Unexporting a Directory for Maintenance

1. Unexport the Directory:

   sudo exportfs -u 192.168.1.100:/srv/nfs

2. Perform Maintenance.

3. Reexport the Directory:

   sudo exportfs 192.168.1.100:/srv/nfs

Security Considerations

• Restrict Access: Always specify specific clients or networks to minimize unauthorized access.

• Monitor Exports: Regularly check the list of exported directories to ensure only intended shares are available.

• Use Secure Options: Utilize options like root_squash to mitigate risks associated with privileged access from clients.

Conclusion

The exportfs command is a powerful tool for managing NFS shares, allowing administrators to export, unexport, and reexport directories efficiently. Proper use of this command, along with careful configuration of /etc/exports, ensures secure and reliable NFS file sharing.