# sysctl settings are defined through files in
# /usr/lib/sysctl.d/, /run/sysctl.d/, and /etc/sysctl.d/.
#
# Vendors settings live in /usr/lib/sysctl.d/.
# To override a whole file, create a new file with the same in
# /etc/sysctl.d/ and put new settings there. To override
# only specific settings, add a file with a lexically later
# name in /etc/sysctl.d/ and put new settings there.
#
# For more information, see sysctl.conf(5) and sysctl.d(5).

### GENERAL SYSTEM SECURITY OPTIONS ###

# Kernel settings
kernel.printk = 4 4 1 7
kernel.panic = 10
kernel.hung_task_panic = 1
kernel.nmi_watchdog = 0
kernel.core_pattern = /var/crash/core.%e.pid_%p.uid_%u.sig_%s

# 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

# Enable ExecShield protection
kernel.randomize_va_space = 2

# Controls the maximum size of a message, in bytes
kernel.msgmnb = 65536

# Controls the default maxmimum size of a mesage queue
kernel.msgmax = 65536

# Restrict core dumps
fs.suid_dumpable = 0

# Hide exposed kernel pointers
kernel.kptr_restrict = 1

### KERNEL FINE TUNNING ###
kernel.sem = 250 256000 64 512

# Configure Kernel Parameter for Accepting ICMP Redirects By Default
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0

# Disable Kernel Parameter for Sending ICMP Redirects for All Interfaces
net.ipv4.conf.all.send_redirects= 0
net.ipv4.conf.default.send_redirects = 0

# Ensure ICMP redirects are not accepted
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.default.secure_redirects = 0

# Enable ip forwarding
net.ipv4.ip_forward = 1

# Enable IP spoofing protection
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.rp_filter = 1

# Ensure source routed packets are not accepted
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0

# Ignoring broadcasts request
net.ipv4.icmp_echo_ignore_broadcasts=1
#net.ipv4.icmp_ignore_bogus_error_messages=1

# Make sure spoofed packets get logged
net.ipv4.conf.all.log_martians = 0

# nginx

# recycle Zombie connections
#net.inet.tcp.fast_finwait2_recycle = 1
#net.inet.tcp.maxtcptw = 200000

# increase number of files
#kern.maxfiles = 65535
#kern.maxfilesperproc = 16384

net.ipv4.tcp_fin_timeout = 30
net.ipv4.ip_local_port_range = 1024 65023

# Increase size of file handles and inode cache
fs.file-max = 2097152

# do less swapping
vm.swappiness = 10
vm.dirty_background_ratio = 1
vm.dirty_ratio = 1
vm.dirty_background_bytes = 5
vm.dirty_bytes = 0
vm.dirty_writeback_centisecs = 500
vm.dirty_expire_centisecs = 3000
vm.vfs_cache_pressure = 50

# specifies the minimum virtual address that a process is allowed to mmap
vm.mmap_min_addr = 4096

# Set maximum amount of memory allocated to shm to 256MB
kernel.shmmax = 268435456
kernel.shmall = 268435456

# Keep at least 64MB of free RAM space available
vm.min_free_kbytes = 65535

# Prevent SYN attack, enable SYNcookies (they will kick-in when the max_syn_backlog reached)
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_syn_retries = 2
net.ipv4.tcp_synack_retries = 2

# increase socket listen backlog
net.core.somaxconn = 32768
net.ipv4.tcp_max_tw_buckets = 1440000

# number of packets to keep in backlog before the kernel starts dropping them
net.ipv4.tcp_max_syn_backlog = 65535

# Decrease the time default value for tcp_fin_timeout connection
net.ipv4.tcp_fin_timeout = 15

# Decrease the time default value for connections to keep alive
net.ipv4.tcp_keepalive_time = 300
net.ipv4.tcp_keepalive_probes = 10
net.ipv4.tcp_keepalive_intvl = 30

# Don't relay bootp
net.ipv4.conf.all.bootp_relay = 0

# Don't proxy arp for anyone
net.ipv4.conf.all.proxy_arp = 0

# Turn on the tcp_timestamps, accurate timestamp make TCP congestion control algorithms work better
net.ipv4.tcp_timestamps = 1

# Don't ignore directed pings
net.ipv4.icmp_echo_ignore_all = 0

# Enable ignoring broadcasts request
net.ipv4.icmp_echo_ignore_broadcasts = 1

# Enable bad error message Protection
#net.ipv4.icmp_ignore_bogus_error_responses = 1

# Enable a fix for RFC1337 - time-wait assassination hazards in TCP
net.ipv4.tcp_rfc1337 = 1
#net.inet.tcp.delayed_ack = 0
#net.inet.tcp.restrict_rst = 1

### TUNING NETWORK PERFORMANCE ###

# For high-bandwidth low-latency networks, use 'htcp' congestion control
# Do a 'modprobe tcp_htcp' first
#net.ipv4.tcp_congestion_control = htcp

# Turn on the tcp_window_scaling
net.ipv4.tcp_window_scaling = 1

# Increase the read-buffer space allocatable
net.ipv4.tcp_rmem = 8192 87380 16777216
net.ipv4.udp_rmem_min = 16384
net.core.rmem_default = 8388608
net.core.rmem_max = 16777216

# Increase the write-buffer-space allocatable
net.ipv4.tcp_wmem = 8192 65536 16777216
net.ipv4.udp_wmem_min = 16384
net.core.wmem_default = 8388608
net.core.wmem_max = 16777216

# Increase number of incoming connections
net.ipv4.tcp_max_tw_buckets = 1440000

# Increase number of incoming connections backlog
net.core.netdev_max_backlog = 16384
net.core.dev_weight = 64

# Increase the maximum amount of option memory buffers
net.core.optmem_max = 25165824

# Limit number of orphans, each orphan can eat up to 16M (max wmem) of unswappable memory
net.ipv4.tcp_max_orphans = 262144
net.ipv4.tcp_orphan_retries = 0

# Increase the maximum memory used to reassemble IP fragments
net.ipv4.ipfrag_high_thresh = 512000
net.ipv4.ipfrag_low_thresh = 446464

# don't cache ssthresh from previous connection
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.tcp_moderate_rcvbuf = 1

# Increase size of RPC datagram queue length
net.unix.max_dgram_qlen = 50

# Don't allow the arp table to become bigger than this
net.ipv4.neigh.default.gc_thresh3 = 2048

# Tell the gc when to become aggressive with arp table cleaning.
# Adjust this based on size of the LAN. 1024 is suitable for most /24 networks
net.ipv4.neigh.default.gc_thresh2 = 1024

# Adjust where the gc will leave arp table alone - set to 32.
net.ipv4.neigh.default.gc_thresh1 = 32

# Adjust to arp table gc to clean-up more often
net.ipv4.neigh.default.gc_interval = 30

# Increase TCP queue length
net.ipv4.neigh.default.proxy_qlen = 96
net.ipv4.neigh.default.unres_qlen = 6
net.ipv4.ip_nonlocal_bind = 1
net.ipv4.tcp_abort_on_overflow = 0

# Enable Explicit Congestion Notification (RFC 3168), disable it if it doesn't work for you
net.ipv4.tcp_ecn = 2
net.ipv4.tcp_reordering = 3

# How many times to retry killing an alive TCP connection
net.ipv4.tcp_retries2 = 15
net.ipv4.tcp_retries1 = 3

# 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

# This will enusre that immediatly subsequent connections use the new values
net.ipv4.route.flush = 1
net.ipv6.route.flush = 1

# mitigate against buffer overflows
#kernel.exec-shield = 1
kernel.randomize_va_space = 2

# maximum number of allowable concurrent requests (default 64K)
#fs.aio-max-nr = 1048576

vm.max_map_count = 262144
vm.overcommit_memory = 1

# congestion control (kernel 4.x)
#net.ipv4.tcp_ecn = 2
#net.core.default_qdisc=fq
#net.ipv4.tcp_congestion_control=bbr