Posted on by Kawin Viriyaprasopsook

Kernel tuning for linux server

Kernel sysctl configuration file for Linux

The following is suitable for dedicated web server, mail, file server etc.
place file in /etc/sysctl.d/60-zercle.conf
and run sysctl --system


# Kernel sysctl configuration file for Linux
# https://www.kernel.org/doc/Documentation/sysctl/
#
# Original by Michiel Klaver <https://klaver.it/linux/sysctl.conf>
# Modify by Kawin Viriyaprasopsook <[email protected]>
#
# The following is suitable for dedicated web server, mail, file server, KVM server etc.
# place file in /etc/sysctl.d/60-sysctl.conf
# and run `sysctl –system`
# ——————————————————————–
# System options
# ——————————————————————–
# Controls IP packet forwarding (Default 0 but docker,vpn,router server must set to 1)
net.ipv4.ip_forward = 0
net.ipv6.conf.all.forwarding = 0
# Addresses of mmap base, heap, stack and VDSO page are randomized
kernel.randomize_va_space = 2
# Controls the System Request debugging functionality of the kernel
kernel.sysrq = 0
# Controls whether core dumps will append the PID to the core filename.
# Useful for debugging multi-threaded applications.
kernel.core_uses_pid = 1
# Allow for more PIDs
kernel.pid_max = 65535
# Changing Semaphore Limits
kernel.msgmni = 1024
kernel.sem = 250 256000 32 1024
# Controls the default maxmimum size of a mesage queue
kernel.msgmnb = 65535
# Controls the maximum size of a message, in bytes
kernel.msgmax = 65535
# Controls the maximum number of shared memory segments, in pages
kernel.shmall = 268435456
# Controls the maximum shared segment size, in bytes
kernel.shmmax = 268435456
# Keep at least 64MB of free RAM space available
vm.min_free_kbytes = 65535
# Controls source route verification
net.ipv4.conf.all.rp_filter = 2
net.ipv4.conf.default.rp_filter = 2
# Do not accept source routing
net.ipv4.conf.default.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0
# Disable ICMP Redirect Acceptance
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0
net.ipv6.conf.all.accept_redirects = 0
net.ipv6.conf.default.accept_redirects = 0
# Disable netfilter on bridges.
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
# Discourage Linux from swapping idle server processes to disk (default = 60)
vm.swappiness = 10
vm.dirty_ratio = 60
vm.dirty_background_ratio = 2
# RFC 1337 fix
net.ipv4.tcp_rfc1337 = 1
# Tweak how the flow of kernel messages is throttled.
#kernel.printk_ratelimit_burst = 10
#kernel.printk_ratelimit = 5
# ——————————————————————–
# The following allow the server to handle lots of connection requests
# ——————————————————————–
# See also http://www.nateware.com/linux-network-tuning-for-2013.html for
# an explanation about some of these parameters, and instructions for
# a few other tweaks outside this file.
# Protection from SYN flood attack.
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_syn_retries = 2
net.ipv4.tcp_synack_retries = 2
# Increase number of incoming connections that can queue up
# before dropping
net.core.somaxconn = 32768
# Handle SYN floods and large numbers of valid HTTPS connections
# https://shehab.tech/
net.ipv4.tcp_max_syn_backlog = 4096
# Increase the length of the network device input queue
net.core.netdev_max_backlog = 16384
# Increase system file descriptor limit so we will (probably)
# never run out under lots of concurrent requests.
# (Per-process limit is set in /etc/security/limits.conf)
fs.file-max = 209708
# Widen the port range used for outgoing connections
net.ipv4.ip_local_port_range = 1024 65535
# Increasing the amount of inotify watchers
fs.inotify.max_user_watches = 524288
# ——————————————————————–
# The following help the server efficiently pipe large amounts of data
# ——————————————————————–
# Disable source routing and redirects
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv6.conf.all.accept_source_route = 0
net.ipv6.conf.default.accept_source_route = 0
# Avoid falling back to slow start after a connection goes idle
# keeps our cwnd large with the keep alive connections (kernel > 3.6)
net.ipv4.tcp_slow_start_after_idle = 0
# Controls TCP Packetization-Layer Path MTU Discovery
net.ipv4.tcp_mtu_probing = 1
# Turn on the tcp_window_scaling
net.ipv4.tcp_window_scaling = 1
# Turn on the tcp_timestamps, accurate timestamp make TCP congestion control algorithms work better
net.ipv4.tcp_timestamps = 1
# Enable the TCP selective acks option for better throughput
net.ipv4.tcp_sack = 1
# Change Congestion Control
# Use BBR TCP congestion control and set tcp_notsent_lowat to 16384 to ensure HTTP/2 prioritization works optimally
# Do a 'modprobe tcp_bbr' first (kernel > 4.9)
# Fall-back to htcp if bbr is unavailable (older kernels)
net.ipv4.tcp_congestion_control = htcp
net.ipv4.tcp_congestion_control = bbr
# bbr + fq for edge compute
net.core.default_qdisc = fq
# if kernel >= 4.13
# bbr + fq_codel better for general purose
#net.core.default_qdisc = fq_codel
# bbr + cake better for WAN gateway
#net.core.default_qdisc = cake
net.ipv4.tcp_notsent_lowat = 16384
# Increase the maximum amount of option memory buffers
net.core.optmem_max = 65535
# Increase Linux autotuning TCP buffer limits
# Set max to 16MB (16777216) for 1GE
# 32M (33554432) or 64M (67108864) for 10GE
# 128M (134217728) or 256M (268435456) for 40GE
# Don't set tcp_mem itself! Let the kernel scale it based on RAM.
# Increase the read-buffer space allocatable
net.ipv4.tcp_rmem = 8192 87380 33554432
net.ipv4.udp_rmem_min = 16384
net.core.rmem_default = 262144
net.core.rmem_max = 67108864
# Increase the write-buffer-space allocatable
net.ipv4.tcp_wmem = 8192 65536 33554432
net.ipv4.udp_wmem_min = 16384
net.core.wmem_default = 262144
net.core.wmem_max = 67108864
# If your servers talk UDP, also up these limits
net.ipv4.udp_rmem_min = 16384
net.ipv4.udp_wmem_min = 16384
# ——————————————————————–
# The following allow the server to handle lots of connection churn
# ——————————————————————–
# Increase the tcp-time-wait buckets pool size to prevent simple DOS attacks
net.ipv4.tcp_max_tw_buckets = 1440000
# Timeout broken connections faster (amount of time to wait for FIN)
net.ipv4.tcp_fin_timeout = 7
# Try to reuse time-wait connections, but don't recycle them (recycle can break clients behind NAT)
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_tw_reuse = 1
# Decrease the time default value for connections to keep alive
# Disconnect dead TCP connections after 600+(60*10) seconds
net.ipv4.tcp_keepalive_time = 600
net.ipv4.tcp_keepalive_probes = 60
net.ipv4.tcp_keepalive_intvl = 10
# This will enusre that immediatly subsequent connections use the new values
net.ipv4.route.flush = 1
net.ipv6.route.flush = 1

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60-zercle.conf

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