sudo truncate -s 0 /etc/sysctl.conf
cat >> /etc/sysctl.conf <<EOF
vm.swappiness=20
net.ipv4.neigh.default.gc_stale_time = 120

# see details in https://help.aliyun.com/knowledge_detail/39428.html
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.default.arp_announce = 2
net.ipv4.conf.lo.arp_announce = 2
net.ipv4.conf.all.arp_announce = 2
# see details in https://help.aliyun.com/knowledge_detail/41334.html
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_max_syn_backlog = 1024
net.ipv4.tcp_synack_retries = 2

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1

kernel.sysrq = 1

net.ipv4.tcp_window_scaling=0
net.ipv4.ip_default_ttl=128
net.ipv4.tcp_timestamps=0
net.ipv4.tcp_window_scaling=0
net.ipv4.ip_default_ttl=128
net.ipv4.tcp_timestamps=0
net.core.rmem_default = 31457280
net.core.wmem_default = 31457280
net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 87380 67108864
net.core.default_qdisc = fq
net.ipv4.tcp_congestion_control = bbr
net.core.somaxconn=65535
net.ipv4.tcp_max_syn_backlog=65535
fs.file-max=100000
EOF
sudo sysctl -p
rm -rf /var/log/boot.log-*
rm -rf /var/log/btmp-*
rm -rf /var/log/cron-*
rm -rf /var/log/dnf.librepo.log-*
rm -rf /var/log/hawkey.log-*
rm -rf /var/log/dnf.log.*
rm -rf /var/log/maillog-*
rm -rf /var/log/secure-*
rm -rf /var/log/spooler-*
rm -rf /var/log/wtmp-*
rm -rf /var/log/messages-*
sudo truncate -s 0 /var/log/syslog
sudo truncate -s 0 /var/log/auth.log
sudo truncate -s 0 /var/log/kern.log
sudo truncate -s 0 /var/log/boot.log
sudo truncate -s 0 /var/log/messages
sudo truncate -s 0 /var/log/v2ray/access.log
sudo journalctl --vacuum-size=50M
free -l
sudo sync; echo 3 > /proc/sys/vm/drop_caches
free -l
netstat -tunap
killall sendmail
sudo ethtool -K eth0 tso on
ifconfig eth0 mtu 1484