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 76And the older cBPF JIT supported on the following archs: 77 78 - mips 79 - sparc 80 81eBPF JITs are a superset of cBPF JITs, meaning the kernel will 82migrate cBPF instructions into eBPF instructions and then JIT 83compile them transparently. Older cBPF JITs can only translate 84tcpdump filters, seccomp rules, etc, but not mentioned eBPF 85programs loaded through bpf(2). 86 87Values: 88 89 - 0 - disable the JIT (default value) 90 - 1 - enable the JIT 91 - 2 - enable the JIT and ask the compiler to emit traces on kernel log. 92 93bpf_jit_harden 94-------------- 95 96This enables hardening for the BPF JIT compiler. Supported are eBPF 97JIT backends. Enabling hardening trades off performance, but can 98mitigate JIT spraying. 99 100Values: 101 102 - 0 - disable JIT hardening (default value) 103 - 1 - enable JIT hardening for unprivileged users only 104 - 2 - enable JIT hardening for all users 105 106where "privileged user" in this context means a process having 107CAP_BPF or CAP_SYS_ADMIN in the root user name space. 108 109bpf_jit_kallsyms 110---------------- 111 112When BPF JIT compiler is enabled, then compiled images are unknown 113addresses to the kernel, meaning they neither show up in traces nor 114in /proc/kallsyms. This enables export of these addresses, which can 115be used for debugging/tracing. If bpf_jit_harden is enabled, this 116feature is disabled. 117 118Values : 119 120 - 0 - disable JIT kallsyms export (default value) 121 - 1 - enable JIT kallsyms export for privileged users only 122 123bpf_jit_limit 124------------- 125 126This enforces a global limit for memory allocations to the BPF JIT 127compiler in order to reject unprivileged JIT requests once it has 128been surpassed. bpf_jit_limit contains the value of the global limit 129in bytes. 130 131dev_weight 132---------- 133 134The maximum number of packets that kernel can handle on a NAPI interrupt, 135it's a Per-CPU variable. For drivers that support LRO or GRO_HW, a hardware 136aggregated packet is counted as one packet in this context. 137 138Default: 64 139 140dev_weight_rx_bias 141------------------ 142 143RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function 144of the driver for the per softirq cycle netdev_budget. This parameter influences 145the proportion of the configured netdev_budget that is spent on RPS based packet 146processing during RX softirq cycles. It is further meant for making current 147dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack. 148(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based 149on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias). 150 151Default: 1 152 153dev_weight_tx_bias 154------------------ 155 156Scales the maximum number of packets that can be processed during a TX softirq cycle. 157Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric 158net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog. 159 160Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias). 161 162Default: 1 163 164default_qdisc 165------------- 166 167The default queuing discipline to use for network devices. This allows 168overriding the default of pfifo_fast with an alternative. Since the default 169queuing discipline is created without additional parameters so is best suited 170to queuing disciplines that work well without configuration like stochastic 171fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use 172queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin 173which require setting up classes and bandwidths. Note that physical multiqueue 174interfaces still use mq as root qdisc, which in turn uses this default for its 175leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead 176default to noqueue. 177 178Default: pfifo_fast 179 180busy_read 181--------- 182 183Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL) 184Approximate time in us to busy loop waiting for packets on the device queue. 185This sets the default value of the SO_BUSY_POLL socket option. 186Can be set or overridden per socket by setting socket option SO_BUSY_POLL, 187which is the preferred method of enabling. If you need to enable the feature 188globally via sysctl, a value of 50 is recommended. 189 190Will increase power usage. 191 192Default: 0 (off) 193 194busy_poll 195---------------- 196Low latency busy poll timeout for poll and select. (needs CONFIG_NET_RX_BUSY_POLL) 197Approximate time in us to busy loop waiting for events. 198Recommended value depends on the number of sockets you poll on. 199For several sockets 50, for several hundreds 100. 200For more than that you probably want to use epoll. 201Note that only sockets with SO_BUSY_POLL set will be busy polled, 202so you want to either selectively set SO_BUSY_POLL on those sockets or set 203sysctl.net.busy_read globally. 204 205Will increase power usage. 206 207Default: 0 (off) 208 209mem_pcpu_rsv 210------------ 211 212Per-cpu reserved forward alloc cache size in page units. Default 1MB per CPU. 213 214rmem_default 215------------ 216 217The default setting of the socket receive buffer in bytes. 218 219rmem_max 220-------- 221 222The maximum receive socket buffer size in bytes. 223 224rps_default_mask 225---------------- 226 227The default RPS CPU mask used on newly created network devices. An empty 228mask means RPS disabled by default. 229 230tstamp_allow_data 231----------------- 232Allow processes to receive tx timestamps looped together with the original 233packet contents. If disabled, transmit timestamp requests from unprivileged 234processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set. 235 236Default: 1 (on) 237 238 239wmem_default 240------------ 241 242The default setting (in bytes) of the socket send buffer. 243 244wmem_max 245-------- 246 247The maximum send socket buffer size in bytes. 248 249message_burst and message_cost 250------------------------------ 251 252These parameters are used to limit the warning messages written to the kernel 253log from the networking code. They enforce a rate limit to make a 254denial-of-service attack impossible. A higher message_cost factor, results in 255fewer messages that will be written. Message_burst controls when messages will 256be dropped. The default settings limit warning messages to one every five 257seconds. 258 259warnings 260-------- 261 262This sysctl is now unused. 263 264This was used to control console messages from the networking stack that 265occur because of problems on the network like duplicate address or bad 266checksums. 267 268These messages are now emitted at KERN_DEBUG and can generally be enabled 269and controlled by the dynamic_debug facility. 270 271netdev_budget 272------------- 273 274Maximum number of packets taken from all interfaces in one polling cycle (NAPI 275poll). In one polling cycle interfaces which are registered to polling are 276probed in a round-robin manner. Also, a polling cycle may not exceed 277netdev_budget_usecs microseconds, even if netdev_budget has not been 278exhausted. 279 280netdev_budget_usecs 281--------------------- 282 283Maximum number of microseconds in one NAPI polling cycle. Polling 284will exit when either netdev_budget_usecs have elapsed during the 285poll cycle or the number of packets processed reaches netdev_budget. 286 287netdev_max_backlog 288------------------ 289 290Maximum number of packets, queued on the INPUT side, when the interface 291receives packets faster than kernel can process them. 292 293netdev_rss_key 294-------------- 295 296RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is 297randomly generated. 298Some user space might need to gather its content even if drivers do not 299provide ethtool -x support yet. 300 301:: 302 303 myhost:~# cat /proc/sys/net/core/netdev_rss_key 304 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) 305 306File contains nul bytes if no driver ever called netdev_rss_key_fill() function. 307 308Note: 309 /proc/sys/net/core/netdev_rss_key contains 52 bytes of key, 310 but most drivers only use 40 bytes of it. 311 312:: 313 314 myhost:~# ethtool -x eth0 315 RX flow hash indirection table for eth0 with 8 RX ring(s): 316 0: 0 1 2 3 4 5 6 7 317 RSS hash key: 318 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:f1:42:89 319 320netdev_tstamp_prequeue 321---------------------- 322 323If set to 0, RX packet timestamps can be sampled after RPS processing, when 324the target CPU processes packets. It might give some delay on timestamps, but 325permit to distribute the load on several cpus. 326 327If set to 1 (default), timestamps are sampled as soon as possible, before 328queueing. 329 330netdev_unregister_timeout_secs 331------------------------------ 332 333Unregister network device timeout in seconds. 334This option controls the timeout (in seconds) used to issue a warning while 335waiting for a network device refcount to drop to 0 during device 336unregistration. A lower value may be useful during bisection to detect 337a leaked reference faster. A larger value may be useful to prevent false 338warnings on slow/loaded systems. 339Default value is 10, minimum 1, maximum 3600. 340 341skb_defer_max 342------------- 343 344Max size (in skbs) of the per-cpu list of skbs being freed 345by the cpu which allocated them. Used by TCP stack so far. 346 347Default: 64 348 349optmem_max 350---------- 351 352Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence 353of struct cmsghdr structures with appended data. TCP tx zerocopy also uses 354optmem_max as a limit for its internal structures. 355 356Default : 128 KB 357 358fb_tunnels_only_for_init_net 359---------------------------- 360 361Controls if fallback tunnels (like tunl0, gre0, gretap0, erspan0, 362sit0, ip6tnl0, ip6gre0) are automatically created. There are 3 possibilities 363(a) value = 0; respective fallback tunnels are created when module is 364loaded in every net namespaces (backward compatible behavior). 365(b) value = 1; [kcmd value: initns] respective fallback tunnels are 366created only in init net namespace and every other net namespace will 367not have them. 368(c) value = 2; [kcmd value: none] fallback tunnels are not created 369when a module is loaded in any of the net namespace. Setting value to 370"2" is pointless after boot if these modules are built-in, so there is 371a kernel command-line option that can change this default. Please refer to 372Documentation/admin-guide/kernel-parameters.txt for additional details. 373 374Not creating fallback tunnels gives control to userspace to create 375whatever is needed only and avoid creating devices which are redundant. 376 377Default : 0 (for compatibility reasons) 378 379devconf_inherit_init_net 380------------------------ 381 382Controls if a new network namespace should inherit all current 383settings under /proc/sys/net/{ipv4,ipv6}/conf/{all,default}/. By 384default, we keep the current behavior: for IPv4 we inherit all current 385settings from init_net and for IPv6 we reset all settings to default. 386 387If set to 1, both IPv4 and IPv6 settings are forced to inherit from 388current ones in init_net. If set to 2, both IPv4 and IPv6 settings are 389forced to reset to their default values. If set to 3, both IPv4 and IPv6 390settings are forced to inherit from current ones in the netns where this 391new netns has been created. 392 393Default : 0 (for compatibility reasons) 394 395txrehash 396-------- 397 398Controls default hash rethink behaviour on socket when SO_TXREHASH option is set 399to SOCK_TXREHASH_DEFAULT (i. e. not overridden by setsockopt). 400 401If set to 1 (default), hash rethink is performed on listening socket. 402If set to 0, hash rethink is not performed. 403 404gro_normal_batch 405---------------- 406 407Maximum number of the segments to batch up on output of GRO. When a packet 408exits GRO, either as a coalesced superframe or as an original packet which 409GRO has decided not to coalesce, it is placed on a per-NAPI list. This 410list is then passed to the stack when the number of segments reaches the 411gro_normal_batch limit. 412 413high_order_alloc_disable 414------------------------ 415 416By default the allocator for page frags tries to use high order pages (order-3 417on x86). While the default behavior gives good results in most cases, some users 418might have hit a contention in page allocations/freeing. This was especially 419true on older kernels (< 5.14) when high-order pages were not stored on per-cpu 420lists. This allows to opt-in for order-0 allocation instead but is now mostly of 421historical importance. 422 423Default: 0 424 4252. /proc/sys/net/unix - Parameters for Unix domain sockets 426---------------------------------------------------------- 427 428There is only one file in this directory. 429unix_dgram_qlen limits the max number of datagrams queued in Unix domain 430socket's buffer. It will not take effect unless PF_UNIX flag is specified. 431 432 4333. /proc/sys/net/ipv4 - IPV4 settings 434------------------------------------- 435Please see: Documentation/networking/ip-sysctl.rst and 436Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 437 438 4394. Appletalk 440------------ 441 442The /proc/sys/net/appletalk directory holds the Appletalk configuration data 443when Appletalk is loaded. The configurable parameters are: 444 445aarp-expiry-time 446---------------- 447 448The amount of time we keep an ARP entry before expiring it. Used to age out 449old hosts. 450 451aarp-resolve-time 452----------------- 453 454The amount of time we will spend trying to resolve an Appletalk address. 455 456aarp-retransmit-limit 457--------------------- 458 459The number of times we will retransmit a query before giving up. 460 461aarp-tick-time 462-------------- 463 464Controls the rate at which expires are checked. 465 466The directory /proc/net/appletalk holds the list of active Appletalk sockets 467on a machine. 468 469The fields indicate the DDP type, the local address (in network:node format) 470the remote address, the size of the transmit pending queue, the size of the 471received queue (bytes waiting for applications to read) the state and the uid 472owning the socket. 473 474/proc/net/atalk_iface lists all the interfaces configured for appletalk.It 475shows the name of the interface, its Appletalk address, the network range on 476that address (or network number for phase 1 networks), and the status of the 477interface. 478 479/proc/net/atalk_route lists each known network route. It lists the target 480(network) that the route leads to, the router (may be directly connected), the 481route flags, and the device the route is using. 482 4835. TIPC 484------- 485 486tipc_rmem 487--------- 488 489The TIPC protocol now has a tunable for the receive memory, similar to the 490tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max) 491 492:: 493 494 # cat /proc/sys/net/tipc/tipc_rmem 495 4252725 34021800 68043600 496 # 497 498The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values 499are scaled (shifted) versions of that same value. Note that the min value 500is not at this point in time used in any meaningful way, but the triplet is 501preserved in order to be consistent with things like tcp_rmem. 502 503named_timeout 504------------- 505 506TIPC name table updates are distributed asynchronously in a cluster, without 507any form of transaction handling. This means that different race scenarios are 508possible. One such is that a name withdrawal sent out by one node and received 509by another node may arrive after a second, overlapping name publication already 510has been accepted from a third node, although the conflicting updates 511originally may have been issued in the correct sequential order. 512If named_timeout is nonzero, failed topology updates will be placed on a defer 513queue until another event arrives that clears the error, or until the timeout 514expires. Value is in milliseconds. 515