Net::SFTP::Foreign->new($ftp_server, port => $ftp_port , user => $ftp_username, password => $ftp_password , key_path => $private_key , more => [ '-v', -o => 'PreferredAuthentications publickey']);


here is verbose log 

debug1: Reading configuration data /home/fds/apfh/.ssh/config

debug1: Reading configuration data /etc/ssh/ssh_config

debug1: Applying options for *

debug1: Connecting to 121.241.2.65 [121.241.2.65] port 6010.

debug1: Connection established.

debug1: identity file /home/fds/apfh/FDSnse_fh/etc/id_rsa type 1

debug1: identity file /home/fds/apfh/FDSnse_fh/etc/id_rsa-cert type -1

debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3

debug1: match: OpenSSH_5.3 pat OpenSSH*

debug1: Enabling compatibility mode for protocol 2.0

debug1: Local version string SSH-2.0-OpenSSH_5.3

debug1: SSH2_MSG_KEXINIT sent

debug1: SSH2_MSG_KEXINIT received

debug1: kex: server->client aes128-ctr hmac-md5 none

debug1: kex: client->server aes128-ctr hmac-md5 none

debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(1024<1024<8192) sent

debug1: expecting SSH2_MSG_KEX_DH_GEX_GROUP

debug1: SSH2_MSG_KEX_DH_GEX_INIT sent

debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY

debug1: Host '[121.241.2.65]:6010' is known and matches the RSA host key.

debug1: Found key in /home/fds/apfh/.ssh/known_hosts:1

debug1: ssh_rsa_verify: signature correct

debug1: SSH2_MSG_NEWKEYS sent

debug1: expecting SSH2_MSG_NEWKEYS

debug1: SSH2_MSG_NEWKEYS received

debug1: SSH2_MSG_SERVICE_REQUEST sent

debug1: SSH2_MSG_SERVICE_ACCEPT received

                                   "NOTICE TO USERS"


            "The system is to be used for AUTHORIZED business purpose only.
        All activities on this system are being monitored. Unauthorized access
             to this system may be subject to legal action,and/or prosecution"

debug1: Authentications that can continue: publickey

debug1: Next authentication method: publickey

debug1: Offering public key: /home/fds/apfh/FDSnse_fh/etc/id_rsa

debug1: Server accepts key: pkalg ssh-rsa blen 277

debug1: read PEM private key done: type RSA

debug1: Authentication succeeded (publickey).

debug1: channel 0: new [client-session]

debug1: Requesting no-more-sessions@openssh.com

debug1: Entering interactive session.

debug1: Sending environment.

debug1: Sending subsystem: sftp

debug1: channel 0: free: client-session, nchannels 1

debug1: fd 0 clearing O_NONBLOCK

debug1: fd 1 clearing O_NONBLOCK

debug1: fd 2 clearing O_NONBLOCK

Connection to 121.241.2.65 closed by remote host.

Transferred: sent 2392, received 2488 bytes, in 30.4 seconds

Bytes per second: sent 78.7, received 81.8

debug1: Exit status -1

ERROR[06/21 13:41:52] fetch_symbology.pl.new:736 Cannot connect to [SFTP] server, error message: SSH slave exited unexpectedly with error code 255 WARN [06/21 13:41:52] fetch_symbology.pl.new:303 [SFTP] connection attempt to server[121.241.2.65] failed, will retry in 60 seconds!