Through the LEAF configuration menu type 2) to get access to the "System configuration" menu:

                        System configuration menu

        1) Master LRP settings. (lrp.conf)
        2) POSIXness settings (POSIXness.conf)
        3) File system mounts. (fstab)
        4) Lowest level boot-up configuration (inittab)
        5) System wide profile (profile)
        6) Ports root is allowed to login to. (securetty)
        7) System logging configuration. (syslog.conf)
        8) Service name to number translation (services)
        9) Local timezone TZ setup (tzvalue)

  q) quit
  ----------------------------------------------------------------------------
        Selection:

Enter 4) to edit inittab. Comment out getty's on tty1 and tty2 and uncomment getty on ttyS0 (com1). For access through com2, com3 or com4 replace by ttyS1, ttyS2 and ttyS3 respectively.

Your inittab file will look like:

<snip>
# Format:
#  <id>:<runlevels>:<action>:<process>
#1:2345:respawn:/sbin/getty 38400 tty1
#2:23:respawn:/sbin/getty 38400 tty2
#3:23:respawn:/sbin/getty 38400 tty3
#4:23:respawn:/sbin/getty 38400 tty4
#5:23:respawn:/sbin/getty 38400 tty5
#6:23:respawn:/sbin/getty 38400 tty6

# Example how to put a getty on a serial line (for a terminal)
#
T1:23:respawn:/sbin/getty -L ttyS0 19200 vt100
<snip>

Enter 6) to edit /etc/securetty to add ttyS0. Your file will look like:

# /etc/securetty: list of terminals on which root is allowed to login.
# See securetty(5) and login(1).
#
# Include ttyp0, ttyp1, etc to allow telnet access. *NOT RECOMMENDED*
ttyS0
tty1
tty2
tty3
tty4
tty5
tty6
tty7
tty8