auto-complete (and history) is part of the bash
shell. You can change to the bash
shell for that user with.
sudo chsh -s /bin/bash $USER
Or for any other shell you like: change the /bin/bash
.
From man useradd
s, --shell SHELL
The name of the user's login shell. The default is to leave this
field blank, which causes the system to select the default login
shell specified by the SHELL variable in /etc/default/useradd, or
an empty string by default.
So you could have used:
useradd -g sybase -d /opt/sybase sybase -s /bin/bash
more /etc/default/useradd
# Default values for useradd(8)
#
# The SHELL variable specifies the default login shell on your
# system.
# Similar to DHSELL in adduser. However, we use "sh" here because
# useradd is a low level utility and should be as general
# as possible
SHELL=/bin/sh