ifname is out of alphabetical order:
unit num
Sets the ppp unit number (for a ppp0 or ppp1 etc interface name)
for outbound connections. If the unit is already in use a dy‐
namically allocated number will be used.
ifname string
Set the ppp interface name for outbound connections. If the in‐
terface name is already in use, or if the name cannot be used
for any other reason, pppd will terminate.
unset name
Remove a variable from the environment variable for scripts that
are invoked by pppd. When specified by a privileged source, the
variable name cannot be set by options contained in an unprivi‐
leged source. See also the set option and the environment de‐
scribed in SCRIPTS.