Read-Only Access

This determines which hosts have read-only access to this share. There are three choices for this option :

None
No hosts have read-only access.
All hosts
Any host can mount this share read-only. If you are connected to the Internet, this means that anyone in the world can read files in the exported directory.
Listed hosts
The hosts or IP addresses listed below can mount this share read-only. Matching hosts listed below can mount this share read-only. Hosts can be specified in the following ways :

Hostname or IP address (like ftp.foo.com or 1.2.3.4)
Matches the host with the given name or address
Netgroup (like engineering)
Matches any host that is a member of the netgroup
DNS domain (like .foo.com)
Matches any host in the domain
Network (like @10.254.1)
Matches any host in the network
Network/netmask (like @10.254.1/24)
Matches any host in the network
In addition, any of the above notations can be prefixed by a -, meaning that the host, netgroup, domain or network is not allowed to mount this share. This can be useful for allowing access by a set of hosts, but denying one member.