agetty is an "alternative getty". It takes all of its parameters on the command line, with no use of /etc/gettydefs or any other configuration file. agetty is documented in the manual page agetty(8).
Figure 6-6 shows how to invoke agetty for use with a serial console.
ttyS0 refers to the serial device /dev/ttyS0.
9600 is the bits per second of the serial link. agetty will support multiple values, using the modem's CONNECT message or the RS-232 Break signal to select between them. Only use one value, as serial consoles only have only one data rate.
vt102 sets the TERM environment variable to indicate that a VT100 terminal is connecting.
-h activates CTS/RTS handshaking.
-t 60 allows 60 seconds for someone to attempt to log in before the modem is hung up. You should test this feature to ensure that init is not restarting agetty every 60 seconds when the link is idle. Look for a continually changing process identifier for agetty.
agetty uses escape sequences in /etc/issue to insert information. For example, \n.\o \l will appear as remote.example.edu.au ttyS0.
When you log out agetty does not appear to lower the Data Terminal Ready signal to force the modme to hang up. If having people automatically disconnected at the end of their login session matters to you then you might consider mgetty instead.