当通过 ssh 连接到我的 ubuntu 16.04 服务器时，我的控制台被如下消息污染：
root@backup ~ # 2017 May 2 15:05:05 backup fatal: Unable to negotiate with XXX port 45700: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1 [preauth]
2017 May 2 15:05:07 backup fatal: Unable to negotiate with XXX port 45991: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1 [preauth]
2017 May 2 15:05:07 backup fatal: Unable to negotiate with XXX port 45981: no matching key exchange method found. Their offer: diffie-hellman-group1-sha1 [preauth]
...
XXX 是外部 IP（不是我的，也不是我的服务器的 IP）。因此，似乎存在对 ssh 服务的字典攻击，这种攻击非常常见。我如何将这些消息发送到日志文件而不是将它们发送到控制台？
编辑
sshd_conf
# Package generated configuration file
# See the sshd_config(5) manpage for details
# What ports, IPs and protocols we listen for
Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes
# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768
# Logging
SyslogFacility AUTH
LogLevel INFO
# Authentication:
LoginGraceTime 120
PermitRootLogin without-password
StrictModes yes
RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile %h/.ssh/authorized_keys
# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes
# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no
# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication yes
# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes
# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes
X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
#MaxStartups 10:30:60
#Banner /etc/issue.net
# Allow client to pass locale environment variables
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication. Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes
#Note that match is effective "until either another Match line or the end of the file."
#(the indentation isn't significant)
Match User rsnapshot
PasswordAuthentication no
编辑
root@backup ~ # sysctl -a | grep kernel.printk
kernel.printk = 4 4 1 7
kernel.printk_delay = 0
kernel.printk_devkmsg = ratelimit
kernel.printk_ratelimit = 5
kernel.printk_ratelimit_burst = 10
sysctl: reading key "net.ipv6.conf.all.stable_secret"
sysctl: reading key "net.ipv6.conf.default.stable_secret"
sysctl: reading key "net.ipv6.conf.eth0.stable_secret"
sysctl: reading key "net.ipv6.conf.lo.stable_secret"