1================================ 2Documentation for /proc/sys/net/ 3================================ 4 5Copyright 6 7Copyright (c) 1999 8 9 - Terrehon Bowden <terrehon@pacbell.net> 10 - Bodo Bauer <bb@ricochet.net> 11 12Copyright (c) 2000 13 14 - Jorge Nerin <comandante@zaralinux.com> 15 16Copyright (c) 2009 17 18 - Shen Feng <shen@cn.fujitsu.com> 19 20For general info and legal blurb, please look in index.rst. 21 22------------------------------------------------------------------------------ 23 24This file contains the documentation for the sysctl files in 25/proc/sys/net 26 27The interface to the networking parts of the kernel is located in 28/proc/sys/net. The following table shows all possible subdirectories. You may 29see only some of them, depending on your kernel's configuration. 30 31 32Table : Subdirectories in /proc/sys/net 33 34 ========= =================== = ========== =================== 35 Directory Content Directory Content 36 ========= =================== = ========== =================== 37 802 E802 protocol mptcp Multipath TCP 38 appletalk Appletalk protocol netfilter Network Filter 39 ax25 AX25 netrom NET/ROM 40 bridge Bridging rose X.25 PLP layer 41 core General parameter tipc TIPC 42 ethernet Ethernet protocol unix Unix domain sockets 43 ipv4 IP version 4 x25 X.25 protocol 44 ipv6 IP version 6 45 ========= =================== = ========== =================== 46 471. /proc/sys/net/core - Network core options 48============================================ 49 50bpf_jit_enable 51-------------- 52 53This enables the BPF Just in Time (JIT) compiler. BPF is a flexible 54and efficient infrastructure allowing to execute bytecode at various 55hook points. It is used in a number of Linux kernel subsystems such 56as networking (e.g. XDP, tc), tracing (e.g. kprobes, uprobes, tracepoints) 57and security (e.g. seccomp). LLVM has a BPF back end that can compile 58restricted C into a sequence of BPF instructions. After program load 59through bpf(2) and passing a verifier in the kernel, a JIT will then 60translate these BPF proglets into native CPU instructions. There are 61two flavors of JITs, the newer eBPF JIT currently supported on: 62 63 - x86_64 64 - x86_32 65 - arm64 66 - arm32 67 - ppc64 68 - ppc32 69 - sparc64 70 - mips64 71 - s390x 72 - riscv64 73 - riscv32 74 - loongarch64 75 - arc 76 77And the older cBPF JIT supported on the following archs: 78 79 - mips 80 - sparc 81 82eBPF JITs are a superset of cBPF JITs, meaning the kernel will 83migrate cBPF instructions into eBPF instructions and then JIT 84compile them transparently. Older cBPF JITs can only translate 85tcpdump filters, seccomp rules, etc, but not mentioned eBPF 86programs loaded through bpf(2). 87 88Values: 89 90 - 0 - disable the JIT (default value) 91 - 1 - enable the JIT 92 - 2 - enable the JIT and ask the compiler to emit traces on kernel log. 93 94bpf_jit_harden 95-------------- 96 97This enables hardening for the BPF JIT compiler. Supported are eBPF 98JIT backends. Enabling hardening trades off performance, but can 99mitigate JIT spraying. 100 101Values: 102 103 - 0 - disable JIT hardening (default value) 104 - 1 - enable JIT hardening for unprivileged users only 105 - 2 - enable JIT hardening for all users 106 107where "privileged user" in this context means a process having 108CAP_BPF or CAP_SYS_ADMIN in the root user name space. 109 110bpf_jit_kallsyms 111---------------- 112 113When BPF JIT compiler is enabled, then compiled images are unknown 114addresses to the kernel, meaning they neither show up in traces nor 115in /proc/kallsyms. This enables export of these addresses, which can 116be used for debugging/tracing. If bpf_jit_harden is enabled, this 117feature is disabled. 118 119Values : 120 121 - 0 - disable JIT kallsyms export (default value) 122 - 1 - enable JIT kallsyms export for privileged users only 123 124bpf_jit_limit 125------------- 126 127This enforces a global limit for memory allocations to the BPF JIT 128compiler in order to reject unprivileged JIT requests once it has 129been surpassed. bpf_jit_limit contains the value of the global limit 130in bytes. 131 132dev_weight 133---------- 134 135The maximum number of packets that kernel can handle on a NAPI interrupt, 136it's a Per-CPU variable. For drivers that support LRO or GRO_HW, a hardware 137aggregated packet is counted as one packet in this context. 138 139Default: 64 140 141dev_weight_rx_bias 142------------------ 143 144RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function 145of the driver for the per softirq cycle netdev_budget. This parameter influences 146the proportion of the configured netdev_budget that is spent on RPS based packet 147processing during RX softirq cycles. It is further meant for making current 148dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack. 149(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based 150on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias). 151 152Default: 1 153 154dev_weight_tx_bias 155------------------ 156 157Scales the maximum number of packets that can be processed during a TX softirq cycle. 158Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric 159net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog. 160 161Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias). 162 163Default: 1 164 165default_qdisc 166------------- 167 168The default queuing discipline to use for network devices. This allows 169overriding the default of pfifo_fast with an alternative. Since the default 170queuing discipline is created without additional parameters so is best suited 171to queuing disciplines that work well without configuration like stochastic 172fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use 173queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin 174which require setting up classes and bandwidths. Note that physical multiqueue 175interfaces still use mq as root qdisc, which in turn uses this default for its 176leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead 177default to noqueue. 178 179Default: pfifo_fast 180 181busy_read 182--------- 183 184Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL) 185Approximate time in us to busy loop waiting for packets on the device queue. 186This sets the default value of the SO_BUSY_POLL socket option. 187Can be set or overridden per socket by setting socket option SO_BUSY_POLL, 188which is the preferred method of enabling. If you need to enable the feature 189globally via sysctl, a value of 50 is recommended. 190 191Will increase power usage. 192 193Default: 0 (off) 194 195busy_poll 196---------------- 197Low latency busy poll timeout for poll and select. (needs CONFIG_NET_RX_BUSY_POLL) 198Approximate time in us to busy loop waiting for events. 199Recommended value depends on the number of sockets you poll on. 200For several sockets 50, for several hundreds 100. 201For more than that you probably want to use epoll. 202Note that only sockets with SO_BUSY_POLL set will be busy polled, 203so you want to either selectively set SO_BUSY_POLL on those sockets or set 204sysctl.net.busy_read globally. 205 206Will increase power usage. 207 208Default: 0 (off) 209 210mem_pcpu_rsv 211------------ 212 213Per-cpu reserved forward alloc cache size in page units. Default 1MB per CPU. 214 215rmem_default 216------------ 217 218The default setting of the socket receive buffer in bytes. 219 220rmem_max 221-------- 222 223The maximum receive socket buffer size in bytes. 224 225rps_default_mask 226---------------- 227 228The default RPS CPU mask used on newly created network devices. An empty 229mask means RPS disabled by default. 230 231tstamp_allow_data 232----------------- 233Allow processes to receive tx timestamps looped together with the original 234packet contents. If disabled, transmit timestamp requests from unprivileged 235processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set. 236 237Default: 1 (on) 238 239 240wmem_default 241------------ 242 243The default setting (in bytes) of the socket send buffer. 244 245wmem_max 246-------- 247 248The maximum send socket buffer size in bytes. 249 250message_burst and message_cost 251------------------------------ 252 253These parameters are used to limit the warning messages written to the kernel 254log from the networking code. They enforce a rate limit to make a 255denial-of-service attack impossible. A higher message_cost factor, results in 256fewer messages that will be written. Message_burst controls when messages will 257be dropped. The default settings limit warning messages to one every five 258seconds. 259 260warnings 261-------- 262 263This sysctl is now unused. 264 265This was used to control console messages from the networking stack that 266occur because of problems on the network like duplicate address or bad 267checksums. 268 269These messages are now emitted at KERN_DEBUG and can generally be enabled 270and controlled by the dynamic_debug facility. 271 272netdev_budget 273------------- 274 275Maximum number of packets taken from all interfaces in one polling cycle (NAPI 276poll). In one polling cycle interfaces which are registered to polling are 277probed in a round-robin manner. Also, a polling cycle may not exceed 278netdev_budget_usecs microseconds, even if netdev_budget has not been 279exhausted. 280 281netdev_budget_usecs 282--------------------- 283 284Maximum number of microseconds in one NAPI polling cycle. Polling 285will exit when either netdev_budget_usecs have elapsed during the 286poll cycle or the number of packets processed reaches netdev_budget. 287 288netdev_max_backlog 289------------------ 290 291Maximum number of packets, queued on the INPUT side, when the interface 292receives packets faster than kernel can process them. 293 294netdev_rss_key 295-------------- 296 297RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is 298randomly generated. 299Some user space might need to gather its content even if drivers do not 300provide ethtool -x support yet. 301 302:: 303 304 myhost:~# cat /proc/sys/net/core/netdev_rss_key 305 84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (52 bytes total) 306 307File contains nul bytes if no driver ever called netdev_rss_key_fill() function. 308 309Note: 310 /proc/sys/net/core/netdev_rss_key contains 52 bytes of key, 311 but most drivers only use 40 bytes of it. 312 313:: 314 315 myhost:~# ethtool -x eth0 316 RX flow hash indirection table for eth0 with 8 RX ring(s): 317 0: 0 1 2 3 4 5 6 7 318 RSS hash key: 319 84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8:43:e3:c9:0c:fd:17:55:c2:3a:4d:69:ed:f1:42:89 320 321netdev_tstamp_prequeue 322---------------------- 323 324If set to 0, RX packet timestamps can be sampled after RPS processing, when 325the target CPU processes packets. It might give some delay on timestamps, but 326permit to distribute the load on several cpus. 327 328If set to 1 (default), timestamps are sampled as soon as possible, before 329queueing. 330 331netdev_unregister_timeout_secs 332------------------------------ 333 334Unregister network device timeout in seconds. 335This option controls the timeout (in seconds) used to issue a warning while 336waiting for a network device refcount to drop to 0 during device 337unregistration. A lower value may be useful during bisection to detect 338a leaked reference faster. A larger value may be useful to prevent false 339warnings on slow/loaded systems. 340Default value is 10, minimum 1, maximum 3600. 341 342skb_defer_max 343------------- 344 345Max size (in skbs) of the per-cpu list of skbs being freed 346by the cpu which allocated them. Used by TCP stack so far. 347 348Default: 64 349 350optmem_max 351---------- 352 353Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence 354of struct cmsghdr structures with appended data. TCP tx zerocopy also uses 355optmem_max as a limit for its internal structures. 356 357Default : 128 KB 358 359fb_tunnels_only_for_init_net 360---------------------------- 361 362Controls if fallback tunnels (like tunl0, gre0, gretap0, erspan0, 363sit0, ip6tnl0, ip6gre0) are automatically created. There are 3 possibilities 364(a) value = 0; respective fallback tunnels are created when module is 365loaded in every net namespaces (backward compatible behavior). 366(b) value = 1; [kcmd value: initns] respective fallback tunnels are 367created only in init net namespace and every other net namespace will 368not have them. 369(c) value = 2; [kcmd value: none] fallback tunnels are not created 370when a module is loaded in any of the net namespace. Setting value to 371"2" is pointless after boot if these modules are built-in, so there is 372a kernel command-line option that can change this default. Please refer to 373Documentation/admin-guide/kernel-parameters.txt for additional details. 374 375Not creating fallback tunnels gives control to userspace to create 376whatever is needed only and avoid creating devices which are redundant. 377 378Default : 0 (for compatibility reasons) 379 380devconf_inherit_init_net 381------------------------ 382 383Controls if a new network namespace should inherit all current 384settings under /proc/sys/net/{ipv4,ipv6}/conf/{all,default}/. By 385default, we keep the current behavior: for IPv4 we inherit all current 386settings from init_net and for IPv6 we reset all settings to default. 387 388If set to 1, both IPv4 and IPv6 settings are forced to inherit from 389current ones in init_net. If set to 2, both IPv4 and IPv6 settings are 390forced to reset to their default values. If set to 3, both IPv4 and IPv6 391settings are forced to inherit from current ones in the netns where this 392new netns has been created. 393 394Default : 0 (for compatibility reasons) 395 396txrehash 397-------- 398 399Controls default hash rethink behaviour on socket when SO_TXREHASH option is set 400to SOCK_TXREHASH_DEFAULT (i. e. not overridden by setsockopt). 401 402If set to 1 (default), hash rethink is performed on listening socket. 403If set to 0, hash rethink is not performed. 404 405gro_normal_batch 406---------------- 407 408Maximum number of the segments to batch up on output of GRO. When a packet 409exits GRO, either as a coalesced superframe or as an original packet which 410GRO has decided not to coalesce, it is placed on a per-NAPI list. This 411list is then passed to the stack when the number of segments reaches the 412gro_normal_batch limit. 413 414high_order_alloc_disable 415------------------------ 416 417By default the allocator for page frags tries to use high order pages (order-3 418on x86). While the default behavior gives good results in most cases, some users 419might have hit a contention in page allocations/freeing. This was especially 420true on older kernels (< 5.14) when high-order pages were not stored on per-cpu 421lists. This allows to opt-in for order-0 allocation instead but is now mostly of 422historical importance. 423 424Default: 0 425 4262. /proc/sys/net/unix - Parameters for Unix domain sockets 427---------------------------------------------------------- 428 429There is only one file in this directory. 430unix_dgram_qlen limits the max number of datagrams queued in Unix domain 431socket's buffer. It will not take effect unless PF_UNIX flag is specified. 432 433 4343. /proc/sys/net/ipv4 - IPV4 settings 435------------------------------------- 436Please see: Documentation/networking/ip-sysctl.rst and 437Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 438 439 4404. Appletalk 441------------ 442 443The /proc/sys/net/appletalk directory holds the Appletalk configuration data 444when Appletalk is loaded. The configurable parameters are: 445 446aarp-expiry-time 447---------------- 448 449The amount of time we keep an ARP entry before expiring it. Used to age out 450old hosts. 451 452aarp-resolve-time 453----------------- 454 455The amount of time we will spend trying to resolve an Appletalk address. 456 457aarp-retransmit-limit 458--------------------- 459 460The number of times we will retransmit a query before giving up. 461 462aarp-tick-time 463-------------- 464 465Controls the rate at which expires are checked. 466 467The directory /proc/net/appletalk holds the list of active Appletalk sockets 468on a machine. 469 470The fields indicate the DDP type, the local address (in network:node format) 471the remote address, the size of the transmit pending queue, the size of the 472received queue (bytes waiting for applications to read) the state and the uid 473owning the socket. 474 475/proc/net/atalk_iface lists all the interfaces configured for appletalk.It 476shows the name of the interface, its Appletalk address, the network range on 477that address (or network number for phase 1 networks), and the status of the 478interface. 479 480/proc/net/atalk_route lists each known network route. It lists the target 481(network) that the route leads to, the router (may be directly connected), the 482route flags, and the device the route is using. 483 4845. TIPC 485------- 486 487tipc_rmem 488--------- 489 490The TIPC protocol now has a tunable for the receive memory, similar to the 491tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max) 492 493:: 494 495 # cat /proc/sys/net/tipc/tipc_rmem 496 4252725 34021800 68043600 497 # 498 499The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values 500are scaled (shifted) versions of that same value. Note that the min value 501is not at this point in time used in any meaningful way, but the triplet is 502preserved in order to be consistent with things like tcp_rmem. 503 504named_timeout 505------------- 506 507TIPC name table updates are distributed asynchronously in a cluster, without 508any form of transaction handling. This means that different race scenarios are 509possible. One such is that a name withdrawal sent out by one node and received 510by another node may arrive after a second, overlapping name publication already 511has been accepted from a third node, although the conflicting updates 512originally may have been issued in the correct sequential order. 513If named_timeout is nonzero, failed topology updates will be placed on a defer 514queue until another event arrives that clears the error, or until the timeout 515expires. Value is in milliseconds. 516