restrict SFTP to a user and specific directory

 create a SSH Subsystem :

#Subsystem      sftp    /usr/lib/openssh/sftp-server
Subsystem sftp internal-sftp
  Match group sftpusers
  ChrootDirectory %h
  ForceCommand internal-sftp

restart ssh server

create a user member of sftpusers:

sudo useradd -g sftpusers -s /sbin/nologin -m -d /directory/to/share username

Apply permissions for Chroot


As ChrootDirectory needs to belong to root and have 755 permissions :

chown root: /directory

chown root: /directory/to

chown root: /directory/to/share

and also apply 755 permissions to these

apply the wanted permissions for the shared directory

chown -R user1:sftpusers /directory/to/share/*