ncutil 3

As seen in previous chapters, a network service has interface and protocol subdirectories associated with it. The interface subdirectory structure may be layered (PPP over a modem or ethernet, for example). The protocol subdirectories represent all those protocols that will function over the interface in question. All of these subdirectories have properties -- key and value combinations -- that provide the necessary configuration information.

How does one know what properties may be assigned to a particular interface or protocol directory? ncutil includes a command that summarizes all of the properties for a directory by key and value type.

Listing 15: The DHCP network service and the property summary for its interface.

[0 ]$ cd 127 [127 DHCP]$ ls drw 128 Built-in Ethernet Interface drw 129 IPv4 Protocol drw 130 DNS Protocol drw 131 IPv6 Protocol drw 132 AppleTalk Protocol drw 133 Proxies Protocol [127 DHCP]$ propsummary 128 -r- (String) bsd-device -rw (Boolean) inactive -r- (String Array) layerable-interfaces -r- (MAC Address) mac-address -rw (String Array) media-options -rw (String Enumeration) media-sub-type = [ 100baseTX | none | 10baseT/UTP | autoselect ] -rw (Ranged Integer) mtu = [ 72 , 1500 ] [127 DHCP]$ propsummary 129 -rw (IPv4 Address Array) broadcast-address -rw (IPv4 Address Array) destination-address -rw (String) dhcp-client-id -rw (Boolean) inactive -rw (IPv4 Address Array) ip-address -rw (String Enumeration) method = [ BOOTP | DHCP | INFORM | LinkLocal | Manual | PPP ] -rw (IPv4 Address) router -rw (IPv4 Address Array) subnet-mask

Listing 15 shows that the Built-in Ethernet interface associated with the DHCP network service has some additional properties associated with it, relative to the properties we saw in its interface template. In particular, the transmission mode, maximum transmission unit, and transmission options are now exposed.

When any network service is created, its interface and protocol directories are populated with default properties and values. To view all of the property keys and values associated with a directory, the read command is used; if no directory ID or path is specified, then the current directory is assumed. If, however, only the value of a particular property is desired, the readprop command is available.

	Listing 16: Using read and readprop.
	[127 DHCP]$ read 129 -rw method = DHCP [127 DHCP]$ readprop 129 method DHCP [127 DHCP]$ setprop 129 dhcp-client-id Verizon [127 DHCP]$ read 129 -rw dhcp-client-id = Verizon -rw method = DHCP [127 DHCP]$ readprop 129 method dhcp-client-id DHCP Verizon

Multiple property keys may be used with the readprop command. In Listing 16 the setprop command is displayed, as well. This command is used to assign a new value to a property, removing any existing value in the process. For properties that take arrays of values, the entire set of values would be replaced by this command. If the user wishes to add values to an existing array-based property, the addval command would be more appropriate.

Listing 17: Adding subnet masks to the IPv4 protocol.

[127 DHCP]$ setprop 129 subnet-mask 255.0.0.0 [127 DHCP]$ addval 129 subnet-mask 255.255.0.0 [127 DHCP]$ read 129 -rw dhcp-client-id = Verizon -rw method = DHCP -rw subnet-mask = { 255.0.0.0 255.255.0.0 } [127 DHCP]$ setprop 129 subnet-mask 255.255.255.0 255.25.0.0 255.0.0.0 [127 DHCP]$ read 129 -rw dhcp-client-id = Verizon -rw method = DHCP -rw subnet-mask = { 255.255.255.0 255.25.0.0 255.0.0.0 }

As Listing 17 shows, setprop completely resets the value of the property. The addval command will accept multiple values, too. The subnet mask "255.25.0.0" was entered incorrectly (missed a 5 in the second byte!) so we need to remove that value and add the appropriate value:

	Listing 18: Removing a value from an array-based property.
	[127 DHCP]$ destroyval 129 subnet-mask 255.25.0.0 [127 DHCP]$ addval 129 subnet-mask 255.255.0.0 [127 DHCP]$ read 129 -rw dhcp-client-id = Verizon -rw method = DHCP -rw subnet-mask = { 255.255.255.0 255.0.0.0 255.255.0.0 }

The destroyval command accepts multiple values for removal; if you remove all values from a property, the property is removed from the directory entirely (in other words, no empty arrays will hang around). A property can be removed completely by using the destroyprop command, rather than by removing all its values.

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