[Debian 12 update!] sysctl config for linux server with 8 GB DDR4 RAM or more, SSD and 1Gbe (or faster) NIC

sysctl.conf

kernel.core_uses_pid = 1
kernel.domainname = your_local_domain_name
kernel.msgmax = 65535
kernel.msgmnb = 65535
kernel.pid_max = 65535
kernel.printk = 2 3 1 2
kernel.randomize_va_space = 2
kernel.shmall = 268435456
kernel.shmmax = 268435456
kernel.sysrq = 0

fs.inotify.max_user_watches = 524288
fs.file-max = 2097152
net.core.default_qdisc = fq_codel
net.core.netdev_max_backlog = 16384
net.core.rmem_default = 33554432
net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.core.wmem_default = 33554432

net.core.somaxconn = 4096
net.core.netdev_max_backlog = 65536
net.core.optmem_max = 25165824

net.ipv4.tcp_rmem = 4096 87380 33554432
net.ipv4.tcp_wmem = 4096 65536 33554432

net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.all.rp_filter = 2
net.ipv4.conf.all.secure_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.default.rp_filter = 2
net.ipv4.conf.default.secure_redirects = 0
net.ipv4.conf.default.send_redirects = 0
net.ipv4.ip_forward = 1

net.ipv4.tcp_congestion_control = bbr
net.ipv4.tcp_fin_timeout = 15
net.ipv4.tcp_keepalive_intvl = 15
net.ipv4.tcp_keepalive_probes = 5
net.ipv4.tcp_keepalive_time = 300
net.ipv4.tcp_max_syn_backlog = 4096
net.ipv4.tcp_max_tw_buckets = 1440000
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_mtu_probing = 1
net.ipv4.tcp_notsent_lowat = 16384
net.ipv4.tcp_rfc1337 = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_slow_start_after_idle = 0
net.ipv4.tcp_syn_retries = 2
net.ipv4.tcp_synack_retries = 2
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps=0
net.ipv4.tcp_sack=1
net.ipv4.tcp_low_latency=1
net.ipv4.tcp_adv_win_scale=1

vm.dirty_background_ratio = 4
vm.dirty_ratio = 5
vm.min_free_kbytes = 65535
vm.overcommit_memory = 1
vm.swappiness = 1

This is in my /etc/sysctl.conf on debian/ubuntu servers after some benchmarks and tests.
You can make these persistent after reboots by
# sysctl -p

Note that when used inside a virtual guest, i.e. KVM VPS etc., you need to consider also doing

ethtool --offload ens3 tx-checksum-ip-generic off
ethtool -K ens3 gro off
ethtool -K ens3 tso off

(where ens3 is your NIC)

You can use /etc/rc.local to make these go live at every boot (put them in rc.local), like, for example;

#!/bin/sh

echo never > /sys/kernel/mm/transparent_hugepage/enabled
echo noop > /sys/block/vda/queue/scheduler
echo 0 > /sys/block/vda/queue/rotational
echo 0 > /sys/block/vda/queue/rq_affinity
echo 9000 > /proc/sys/vm/dirty_expire_centisecs
echo 9000 > /proc/sys/vm/dirty_writeback_centisecs

ethtool --offload ens3 tx-checksum-ip-generic off
ethtool -K ens3 gro off
ethtool -K ens3 tso off

exit 0

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

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

Often this doesn't have the effect you want it to have. What worked for me was putting

GRUB_CMDLINE_LINUX_DEFAULT="ipv6.disable=1 quiet splash"

in /etc/default/grub

Don't forget to run update-grub afterwards..

net.ipv4.tcp_timestamps is set twice:

net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 0

net.ipv4.tcp_timestamps is set twice:

net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 0

Yes, I'd left that one in, because I wasn't sure of either option yet. As you can see in the gist's history, it was part of the lastly added entries.

Would it be useful to add?

## /etc/security/limits.conf
## System Limits for FDs
## "nofile" is "Number of Open Files" 
## This is the cap on number of FDs in use concurrently.
## Set nofile to the max value of 1,048,576.

#<user>     <type>    <item>     <value>
*           soft      nofile     1048576
*           hard      nofile     1048576
root        soft      nofile     1048576
root        hard      nofile     1048576 

From https://www.linkedin.com/pulse/ec2-tuning-1m-tcp-connections-using-linux-stephen-blum/

Its also mentioned here: https://www.wikitechy.com/tutorials/linux/how-to-change-the-number-of-open-files-limit-in-linux