Specifications

Background Image
To easily identify a computer that has been NetBooted, it is helpful to have
a special background image. Suffield has such an image, stored in the Tech
Repair folder on the server.
To install an image on the master machine, copy it onto the computer and name
it DefaultDesktop.jpg. Move the file into the folder /System/Library/CoreServices/,
replacing any existing version.
Disabling Network Authentication
By default, our DHCP server advertises an LDAP server to all booted clients.
This LDAP server helps with network authentication, servers, printers, and
other centralized services.
Because the rescue image is not really multi-user, we don’t need many of these
authentication-related services. Additionally, they just slow down the operation
of the system when not needed. Therefore, we disable these services for the
rescue image.
To disable LDAP authentication, open the Directory Access program in
/Applications/Utilities. Click the LDAPv3 service and click the config-
ure button to access the settings. In the window that appears, deselect the Add
DHCP-supplied LDAP servers to automatic search policies checkbox.
Click OK to save your changes.
Network Speed Tweaks
By default, Mac OS X comes with conservative networking settings that do
not maximize performance over fast (100Mb/s and up) links. Since most of our
NetBooted machines will be on a link that is at least this fast, we apply some
tweaks to increase the performance of the networking stack.
To do this, edit (or create, if it does not exist) the file /etc/sysctl.conf. Add
the following lines:
net.inet.tcp.mssdflt=1460
net.inet.tcp.sendspace=1048576
net.inet.tcp.recvspace=1048576
net.inet.udp.recvspace=65535
net.inet.udp.maxdgram=57344
kern.ipc.maxsockbuf=10485760
net.inet.tcp.newreno=1
net.inet.tcp.always_keepalive=1
net.inet.tcp.keepidle=3600
12