init.

rc.d script.

SysV type.

/etc/init.d/*

Here scripts.

/etc/rc<N>.d/[SK]<NN>name

Here symlink to /etc/init.d/ scripts. <N> - runlevel, <NN> - start order from low to high, with K run stop, with S run start.

To disable the service, rename the symbolic link so that its name begins with a K instead of with an S and its sequence number is 100 minus NN.

Managing services.

$ sudo service start $NAME
$ sudo service stop $NAME
$ sudo service restart $NAME
$ sudo service force-reload $NAME

How manage runlevel for startup script.

For Debian preferred package is sysvconfig(8).

See also bum(8) or update-rc.d(8) or sysv-rc-conf(8).