그래서 찾아보니 막아야한다고한다..
#vi /etc/ssh/sshd_config
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Subsystem sftp /usr/lib/openssh/sftp-server
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Subsystem sftp /usr/lib/openssh/sftp-server 를 주석처리해준다..
#Subsystem sftp /usr/lib/openssh/sftp-server