[Debian 12 update!] sysctl config for linux server with 32 GB DDR RAM or more, SSD and 1Gbe (or faster) NIC

sysctl.conf

# IPv6 Configuration
# -> note that I have disabled ip6 for our internet-connection (wan/eth0) because
# -> my upstream/ISP (still) does not do IPv6. The rest, even localhost, does ip6 stuff.
net.ipv6.conf.all.disable_ipv6 = 0
net.ipv6.conf.default.disable_ipv6 = 0
net.ipv6.conf.lo.disable_ipv6 = 0
net.ipv6.conf.eth0.disable_ipv6 = 1
net.ipv6.conf.wan.disable_ipv6 = 1

# Packet Forwarding
net.ipv4.ip_forward = 1

# Security Settings
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.default.accept_redirects = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv4.conf.default.send_redirects = 0

# Connection Tracking
net.netfilter.nf_conntrack_max = 1048576
net.netfilter.nf_conntrack_buckets = 262144
net.netfilter.nf_conntrack_tcp_timeout_established = 86400
net.netfilter.nf_conntrack_tcp_timeout_time_wait = 30

# Socket Buffer Sizes
net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 65536 67108864
net.core.rmem_default = 524288
net.core.wmem_default = 524288

# Backlog and Queuing
net.core.netdev_max_backlog = 60000
net.core.netdev_budget = 120000
net.core.netdev_budget_usecs = 48000
net.core.optmem_max = 8388608
net.core.default_qdisc = fq_codel

# TCP Settings
net.ipv4.tcp_congestion_control = bbr
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_fastopen = 3
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 5
net.ipv4.tcp_max_syn_backlog = 16384
net.ipv4.tcp_mtu_probing = 1
net.ipv4.tcp_slow_start_after_idle = 0
net.ipv4.tcp_retries2 = 5
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_low_latency = 1
net.ipv4.tcp_adv_win_scale = 1

# Memory Settings
vm.min_free_kbytes = 524288
vm.swappiness = 0
vm.dirty_background_ratio = 5
vm.dirty_ratio = 10
vm.dirty_expire_centisecs = 3000
vm.dirty_writeback_centisecs = 500

# File Descriptors
fs.file-max = 2097152
fs.nr_open = 2097152

# Inotify Watches
fs.inotify.max_user_watches = 1048576

# Shared Memory Limits
kernel.shmmax = 17179869184
kernel.shmall = 4194304

# Kernel Miscellaneous
kernel.core_uses_pid = 1
kernel.domainname = your.local.server.domain.name
kernel.printk = 3 4 1 3
kernel.randomize_va_space = 2
kernel.sysrq = 0

what would you want to change for a 16gb system

what would you want to change for a 16gb system

or 64 ;)?

I just updated/upgraded the sysctl entries to fully use the RAM available. Should also do well with 16 and 64 GB, depending on how much of your RAM is already in use. In my experience, linux is rather sparse in using plenty of RAM on servers when it's there, unless you're doing a lot of database caching or forced RAMdisks and the likes. I still use log2ram a lot, for example, which works well for making sure certain folders are entirely IO from RAM (often still 5 x as fast as SSD/NVME).

Nice thanks! I have alked my fav LLM to comment on the lines with defaults and human readable numbers.

# IPv6 Configuration
# -> Note that I have disabled IPv6 for our internet connection (wan/eth0) 
# -> because my ISP (still) does not support IPv6. The rest, including localhost, uses IPv6.
net.ipv6.conf.all.disable_ipv6 = 0  # Default: 0
net.ipv6.conf.default.disable_ipv6 = 0  # Default: 0
net.ipv6.conf.lo.disable_ipv6 = 0  # Default: 0
net.ipv6.conf.eth0.disable_ipv6 = 1  # Default: 0
net.ipv6.conf.wan.disable_ipv6 = 1  # Default: 0

# Packet Forwarding
net.ipv4.ip_forward = 1  # Default: 0

# Security Settings
net.ipv4.conf.all.accept_redirects = 0  # Default: 1
net.ipv4.conf.default.accept_redirects = 0  # Default: 1
net.ipv4.conf.all.accept_source_route = 0  # Default: 0
net.ipv4.conf.default.accept_source_route = 0  # Default: 0
net.ipv4.conf.all.send_redirects = 0  # Default: 1
net.ipv4.conf.default.send_redirects = 0  # Default: 1

# Connection Tracking
net.netfilter.nf_conntrack_max = 1048576  # 1M connections (Default: ~65536)
net.netfilter.nf_conntrack_buckets = 262144  # 256K buckets (Default: ~16384)
net.netfilter.nf_conntrack_tcp_timeout_established = 86400  # 24h (Default: 432000)
net.netfilter.nf_conntrack_tcp_timeout_time_wait = 30  # 30 sec (Default: 120)

# Socket Buffer Sizes
net.core.rmem_max = 67108864  # 64 MB (Default: 212992)
net.core.wmem_max = 67108864  # 64 MB (Default: 212992)
net.ipv4.tcp_rmem = 4096 87380 67108864  # Min: 4 KB, Default: 87 KB, Max: 64 MB (Default: 4096 87380 6291456)
net.ipv4.tcp_wmem = 4096 65536 67108864  # Min: 4 KB, Default: 64 KB, Max: 64 MB (Default: 4096 16384 4194304)
net.core.rmem_default = 524288  # 512 KB (Default: 212992)
net.core.wmem_default = 524288  # 512 KB (Default: 212992)

# Backlog and Queuing
net.core.netdev_max_backlog = 60000  # Default: 1000
net.core.netdev_budget = 120000  # Default: 300
net.core.netdev_budget_usecs = 48000  # Default: 2000
net.core.optmem_max = 8388608  # 8 MB (Default: 20480)
net.core.default_qdisc = fq_codel  # Default: pfifo_fast

# TCP Settings
net.ipv4.tcp_congestion_control = bbr  # Default: cubic
net.ipv4.tcp_window_scaling = 1  # Default: 1
net.ipv4.tcp_sack = 1  # Default: 1
net.ipv4.tcp_fastopen = 3  # Default: 1
net.ipv4.tcp_tw_reuse = 1  # Default: 0
net.ipv4.tcp_fin_timeout = 5  # Default: 60
net.ipv4.tcp_max_syn_backlog = 16384  # Default: 1024
net.ipv4.tcp_mtu_probing = 1  # Default: 0
net.ipv4.tcp_slow_start_after_idle = 0  # Default: 1
net.ipv4.tcp_retries2 = 5  # Default: 15
net.ipv4.tcp_timestamps = 0  # Default: 1
net.ipv4.tcp_sack = 1  # Default: 1
net.ipv4.tcp_low_latency = 1  # Default: 0
net.ipv4.tcp_adv_win_scale = 1  # Default: 2

# Memory Settings
vm.min_free_kbytes = 524288  # 512 MB (Default: varies by system RAM)
vm.swappiness = 0  # Default: 60
vm.dirty_background_ratio = 5  # Default: 10
vm.dirty_ratio = 10  # Default: 20
vm.dirty_expire_centisecs = 3000  # 30 sec (Default: 3000)
vm.dirty_writeback_centisecs = 500  # 5 sec (Default: 500)

# File Descriptors
fs.file-max = 2097152  # ~2M file descriptors (Default: varies, often ~100000)
fs.nr_open = 2097152  # ~2M open files per process (Default: 1048576)

# Inotify Watches
fs.inotify.max_user_watches = 1048576  # 1M watches (Default: 8192)

# Shared Memory Limits
kernel.shmmax = 17179869184  # 16 GB (Default: 33554432 / 32 MB)
kernel.shmall = 4194304  # 4M pages (~16 GB total) (Default: varies)

# Kernel Miscellaneous
kernel.core_uses_pid = 1  # Default: 1
kernel.domainname = your.local.server.domain.name  # Default: (empty)
kernel.printk = 3 4 1 3  # Default: 4 4 1 7
kernel.randomize_va_space = 2  # Default: 2
kernel.sysrq = 0  # Default: 176

thanks! You are best

Nice thanks! I have alked my fav LLM to comment on the lines with defaults and human readable numbers.

net.core.default_qdisc = fq_codel  # Default: pfifo_fast
net.ipv4.tcp_congestion_control = bbr  # Default: cubic
kernel.printk = 3 4 1 3  # Default: 4 4 1 7

Did you specify a version and linux distribution, and which LLM did you ask? All I can say is: Do not rely on LLM for debian config. Can be pretty disastrous. Colleague of mine brought down entire clusters using LLM provided config..