Linux System Optimization

OpenSSH

grep -E 'GSSAPIAuthentication|UseDNS' /etc/ssh/sshd_config

# Remove existing GSSAPIAuthentication and UseDNS lines to prevent duplicates
sed -i '/^GSSAPIAuthentication/d' /etc/ssh/sshd_config
sed -i '/^UseDNS/d' /etc/ssh/sshd_config

# Disable GSSAPIAuthentication and UseDNS
cat >>/etc/ssh/sshd_config <<EOF
GSSAPIAuthentication no
UseDNS no
EOF

systemctl restart sshd.service

History Command

Enable timestamp in history command.

~]# mkdir /var/log/history.d
~]# touch /var/log/history.d/history
~]# chmod 666 /var/log/history.d/history
~]# cat > /etc/profile.d/history.sh << "EOF"
shopt -s histappend
HISTTIMEFORMAT='%F %T '
HISTSIZE="5000"
HISTFILESIZE=5000
PROMPT_COMMAND='(umask 000; msg=$(history 1 | { read x y; echo $y; }); echo [$(who am i | awk "{print \$(NF-2),\$(NF-1),\$NF}")] [$(whoami)@`pwd`]" $msg" >>/var/log/history.d/history)'
export HISTTIMEFORMAT HISTSIZE HISTFILESIZE PROMPT_COMMAND
EOF