Linux user SCP only
install rssh:
apt-get install rssh
then to add a user:
useradd -m -d /home/didi -s /usr/bin/rssh didi
edit
nano /etc/rssh.conf
and select how much users are locked out:
allowscp
#allowsftp
#allowcvs
#allowrdist
#allowrsync
#allowsvnserve
source: https://www.cyberciti.biz/tips/linux-unix-restrict-shell-access-with-rssh.html