Exporting or Sharing NFS File Systems

Sharing or serving files from an NFS server is known as exporting the directories. The NFS Server Configuration Tool can be used to configure a system as an NFS server.

To add an NFS share, click the Add button. The dialog box shown in Figure 20.3, "Add Share" appears.

The Basic tab requires the following information:

• Directory - Specify the directory to share, such as /tmp.

• Host(s) - Specify the host(s) with which to share the directory. Refer to "Hostname Formats" for an explanation of possible formats.
• Basic permissions - Specify whether the directory should have read-only or read/write permissions.

Figure 20.3. Add Share

The General Options tab allows the following options to be configured:

Figure 20.4. NFS General Options

• Allow connections from port 1024 and higher - Services started on port numbers less than 1024 must be started as root. Select this option to allow the NFS service to be started by a user other than root. This option corresponds to insecure.

• Allow insecure file locking - Do not require a lock request. This option corresponds to insecure_locks.
• Disable subtree checking - If a subdirectory of a file system is exported, but the entire file system is not exported, the server checks to see if the requested file is in the subdirectory exported. This check is called subtree checking. Select this option to disable subtree checking. If the entire file system is exported, selecting to disable subtree checking can increase the transfer rate. This option corresponds to no_subtree_check.
• Sync write operations on request - Enabled by default, this option does not allow the server to reply to requests before the changes made by the request are written to the disk. This option corresponds to sync. If this is not selected, the async option is used.
  • Force sync of write operations immediately - Do not delay writing to disk. This option corresponds to no_wdelay.

• Hide filesystems beneath turns the nohide option on or off. When the nohide option is off, nested directories are revealed. The clients can therefore navigate through a filesystem from the parent without noticing any changes.
• Export only if mounted sets the mountpoint option which allows a directory to be exported only if it has been mounted.
• Optional Mount Point specifies the path to an optional mount point. Click on the Browse to navigate to the preferred mount point or type the path if known.
• Set explicit Filesystem ID: sets the fsid=X option. This is mainly used in a clustered setup. Using a consistent filesystem ID in all clusters avoids having stale NFS filehandles.

Figure 20.5. NFS User Access

The User Access tab allows the following options to be configured:

• Treat remote root user as local root - By default, the user and group IDs of the root user are both 0. Root squashing maps the user ID 0 and the group ID 0 to the user and group IDs of anonymous so that root on the client does not have root privileges on the NFS server. If this option is selected, root is not mapped to anonymous, and root on a client has root privileges to exported directories. Selecting this option can greatly decrease the security of the system. Do not select it unless it is absolutely necessary. This option corresponds to no_root_squash.

• Treat all client users as anonymous users - If this option is selected, all user and group IDs are mapped to the anonymous user. This option corresponds to all_squash.
  • Specify local user ID for anonymous users - If Treat all client users as anonymous users is selected, this option lets you specify a user ID for the anonymous user. This option corresponds to anonuid.
• Specify local group ID for anonymous users - If Treat all client users as anonymous users is selected, this option lets you specify a group ID for the anonymous user. This option corresponds to anongid.

To edit an existing NFS share, select the share from the list, and click the Properties button. To delete an existing NFS share, select the share from the list, and click the Delete button.

After clicking OK to add, edit, or delete an NFS share from the list, the changes take place immediately - the server daemon is restarted and the old configuration file is saved as /etc/exports.bak. The new configuration is written to /etc/exports.

The NFS Server Configuration Tool reads and writes directly to the /etc/exports configuration file. Thus, the file can be modified manually after using the tool, and the tool can be used after modifying the file manually (provided the file was modified with correct syntax).

The next this section discusses manually editing /etc/exports and using the /usr/sbin/exportfs command to export NFS file systems.