- Systems administration of remote computers
Linux is a good
operating system for deployment at unstaffed sites. Linux is also good for hosting
critical network infrastructure such as DNS
and DHCP services. These services are
generally installed at every site of an organisation including
sites which may be too small or too remote to have information
technology staff.
System administration of these remote computers is usually
done using SSH, but
there are times when access to the console is the only way to
diagnose and correct software failures. Major upgrades to the
installed distribution may also require console access.
In these cases the serial console is attached to a modem.
Access to the console is gained from a remote computer by
dialing into the modem. This allows the console to be reached
from any telephone socket.
- High density racks of computers
Clusters of personal computers can outperform mainframe
computers and form competitive supercomputers for some
applications. See the Cluster-HOWTO
for more information on clustering.
These clusters are typically assembled into 19 inch
telecommunications equipment racks and the system unit of each
computer is typically one rack unit (or 1.75 inches) tall. It
is not desirable to put a keyboard and monitor on each computer,
as a small cathode ray tube monitor would consume the space used
by sixteen rack units.
A first glance it seems that a monitor and keyboard switch
is the best solution. However the VGA signal
to the monitor is small, so even with the switch the monitor
cannot be placed very far away from the rack of
computers.
It is desirable to allow the consoles to be monitored in
the operators' room of the computer center, rather than in the
very expensive space of the machine room. Although monitor
switches with remote control and fiber optical extensions are
available, this solution can be expensive.
A standard RS-232 cable can be 15
meters in length. Longer distances are easily possible. The
cabling is cheap. Terminal servers can be used to allow one
terminal to access up to 90 serial consoles.
- Recording console messages
This is useful in two very different cases.
Kernel programmers are often faced with a kernel error
message that is displayed a split second before the computer
reboots. A serial console can be used to record that
message. Another Linux
machine can be used as the serial terminal.
Some secure installations require all security events to
be unalterably logged. One way to meet this requirement is to
print all console messages. Connecting the serial console to a
serial printer can achieve this.
- Embedded software development
Linux is
increasingly being used as an operating system for embedded
applications. These computers do not have keyboards or
screens.
A serial port is a cheap way to allow software developers
to directly access the embedded computer. This is invaluable
for debugging. Most chip sets designed for embedded computers
have a serial port precisely for this purpose.
The shipping product need not present the
RS-232 port on an external connector.
Alternatively the RS-232 port is often used for
downloading software updates.
- Craft terminal for telecommunications equipment
Linux is
increasingly being used as the operating system inside
telecommunications equipment. The Carrier Grade
Linux consortia hopes to accelerate and coordinate this
trend.
Most telecommunications equipment is remotely managed from
a distant computer. However, site technicans (called
craft personnel in telco-speak) need to
access the equipment to test installation changes, check the
status of reported faults, and so on. The terminal used by the
craft personnel is called the craft
terminal. The craft terminal plugs into the
craft interface on the equipment. The
serial console makes an ideal craft interface.