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 209rmem_default 210------------ 211 212The default setting of the socket receive buffer in bytes. 213 214rmem_max 215-------- 216 217The maximum receive socket buffer size in bytes. 218 219rps_default_mask 220---------------- 221 222The default RPS CPU mask used on newly created network devices. An empty 223mask means RPS disabled by default. 224 225tstamp_allow_data 226----------------- 227Allow processes to receive tx timestamps looped together with the original 228packet contents. If disabled, transmit timestamp requests from unprivileged 229processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set. 230 231Default: 1 (on) 232 233 234wmem_default 235------------ 236 237The default setting (in bytes) of the socket send buffer. 238 239wmem_max 240-------- 241 242The maximum send socket buffer size in bytes. 243 244message_burst and message_cost 245------------------------------ 246 247These parameters are used to limit the warning messages written to the kernel 248log from the networking code. They enforce a rate limit to make a 249denial-of-service attack impossible. A higher message_cost factor, results in 250fewer messages that will be written. Message_burst controls when messages will 251be dropped. The default settings limit warning messages to one every five 252seconds. 253 254warnings 255-------- 256 257This sysctl is now unused. 258 259This was used to control console messages from the networking stack that 260occur because of problems on the network like duplicate address or bad 261checksums. 262 263These messages are now emitted at KERN_DEBUG and can generally be enabled 264and controlled by the dynamic_debug facility. 265 266netdev_budget 267------------- 268 269Maximum number of packets taken from all interfaces in one polling cycle (NAPI 270poll). In one polling cycle interfaces which are registered to polling are 271probed in a round-robin manner. Also, a polling cycle may not exceed 272netdev_budget_usecs microseconds, even if netdev_budget has not been 273exhausted. 274 275netdev_budget_usecs 276--------------------- 277 278Maximum number of microseconds in one NAPI polling cycle. Polling 279will exit when either netdev_budget_usecs have elapsed during the 280poll cycle or the number of packets processed reaches netdev_budget. 281 282netdev_max_backlog 283------------------ 284 285Maximum number of packets, queued on the INPUT side, when the interface 286receives packets faster than kernel can process them. 287 288netdev_rss_key 289-------------- 290 291RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is 292randomly generated. 293Some user space might need to gather its content even if drivers do not 294provide ethtool -x support yet. 295 296:: 297 298 myhost:~# cat /proc/sys/net/core/netdev_rss_key 299 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) 300 301File contains nul bytes if no driver ever called netdev_rss_key_fill() function. 302 303Note: 304 /proc/sys/net/core/netdev_rss_key contains 52 bytes of key, 305 but most drivers only use 40 bytes of it. 306 307:: 308 309 myhost:~# ethtool -x eth0 310 RX flow hash indirection table for eth0 with 8 RX ring(s): 311 0: 0 1 2 3 4 5 6 7 312 RSS hash key: 313 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:f1:42:89 314 315netdev_tstamp_prequeue 316---------------------- 317 318If set to 0, RX packet timestamps can be sampled after RPS processing, when 319the target CPU processes packets. It might give some delay on timestamps, but 320permit to distribute the load on several cpus. 321 322If set to 1 (default), timestamps are sampled as soon as possible, before 323queueing. 324 325netdev_unregister_timeout_secs 326------------------------------ 327 328Unregister network device timeout in seconds. 329This option controls the timeout (in seconds) used to issue a warning while 330waiting for a network device refcount to drop to 0 during device 331unregistration. A lower value may be useful during bisection to detect 332a leaked reference faster. A larger value may be useful to prevent false 333warnings on slow/loaded systems. 334Default value is 10, minimum 1, maximum 3600. 335 336skb_defer_max 337------------- 338 339Max size (in skbs) of the per-cpu list of skbs being freed 340by the cpu which allocated them. Used by TCP stack so far. 341 342Default: 64 343 344optmem_max 345---------- 346 347Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence 348of struct cmsghdr structures with appended data. 349 350fb_tunnels_only_for_init_net 351---------------------------- 352 353Controls if fallback tunnels (like tunl0, gre0, gretap0, erspan0, 354sit0, ip6tnl0, ip6gre0) are automatically created. There are 3 possibilities 355(a) value = 0; respective fallback tunnels are created when module is 356loaded in every net namespaces (backward compatible behavior). 357(b) value = 1; [kcmd value: initns] respective fallback tunnels are 358created only in init net namespace and every other net namespace will 359not have them. 360(c) value = 2; [kcmd value: none] fallback tunnels are not created 361when a module is loaded in any of the net namespace. Setting value to 362"2" is pointless after boot if these modules are built-in, so there is 363a kernel command-line option that can change this default. Please refer to 364Documentation/admin-guide/kernel-parameters.txt for additional details. 365 366Not creating fallback tunnels gives control to userspace to create 367whatever is needed only and avoid creating devices which are redundant. 368 369Default : 0 (for compatibility reasons) 370 371devconf_inherit_init_net 372------------------------ 373 374Controls if a new network namespace should inherit all current 375settings under /proc/sys/net/{ipv4,ipv6}/conf/{all,default}/. By 376default, we keep the current behavior: for IPv4 we inherit all current 377settings from init_net and for IPv6 we reset all settings to default. 378 379If set to 1, both IPv4 and IPv6 settings are forced to inherit from 380current ones in init_net. If set to 2, both IPv4 and IPv6 settings are 381forced to reset to their default values. If set to 3, both IPv4 and IPv6 382settings are forced to inherit from current ones in the netns where this 383new netns has been created. 384 385Default : 0 (for compatibility reasons) 386 387txrehash 388-------- 389 390Controls default hash rethink behaviour on socket when SO_TXREHASH option is set 391to SOCK_TXREHASH_DEFAULT (i. e. not overridden by setsockopt). 392 393If set to 1 (default), hash rethink is performed on listening socket. 394If set to 0, hash rethink is not performed. 395 396gro_normal_batch 397---------------- 398 399Maximum number of the segments to batch up on output of GRO. When a packet 400exits GRO, either as a coalesced superframe or as an original packet which 401GRO has decided not to coalesce, it is placed on a per-NAPI list. This 402list is then passed to the stack when the number of segments reaches the 403gro_normal_batch limit. 404 405high_order_alloc_disable 406------------------------ 407 408By default the allocator for page frags tries to use high order pages (order-3 409on x86). While the default behavior gives good results in most cases, some users 410might have hit a contention in page allocations/freeing. This was especially 411true on older kernels (< 5.14) when high-order pages were not stored on per-cpu 412lists. This allows to opt-in for order-0 allocation instead but is now mostly of 413historical importance. 414 415Default: 0 416 4172. /proc/sys/net/unix - Parameters for Unix domain sockets 418---------------------------------------------------------- 419 420There is only one file in this directory. 421unix_dgram_qlen limits the max number of datagrams queued in Unix domain 422socket's buffer. It will not take effect unless PF_UNIX flag is specified. 423 424 4253. /proc/sys/net/ipv4 - IPV4 settings 426------------------------------------- 427Please see: Documentation/networking/ip-sysctl.rst and 428Documentation/admin-guide/sysctl/net.rst for descriptions of these entries. 429 430 4314. Appletalk 432------------ 433 434The /proc/sys/net/appletalk directory holds the Appletalk configuration data 435when Appletalk is loaded. The configurable parameters are: 436 437aarp-expiry-time 438---------------- 439 440The amount of time we keep an ARP entry before expiring it. Used to age out 441old hosts. 442 443aarp-resolve-time 444----------------- 445 446The amount of time we will spend trying to resolve an Appletalk address. 447 448aarp-retransmit-limit 449--------------------- 450 451The number of times we will retransmit a query before giving up. 452 453aarp-tick-time 454-------------- 455 456Controls the rate at which expires are checked. 457 458The directory /proc/net/appletalk holds the list of active Appletalk sockets 459on a machine. 460 461The fields indicate the DDP type, the local address (in network:node format) 462the remote address, the size of the transmit pending queue, the size of the 463received queue (bytes waiting for applications to read) the state and the uid 464owning the socket. 465 466/proc/net/atalk_iface lists all the interfaces configured for appletalk.It 467shows the name of the interface, its Appletalk address, the network range on 468that address (or network number for phase 1 networks), and the status of the 469interface. 470 471/proc/net/atalk_route lists each known network route. It lists the target 472(network) that the route leads to, the router (may be directly connected), the 473route flags, and the device the route is using. 474 4755. TIPC 476------- 477 478tipc_rmem 479--------- 480 481The TIPC protocol now has a tunable for the receive memory, similar to the 482tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max) 483 484:: 485 486 # cat /proc/sys/net/tipc/tipc_rmem 487 4252725 34021800 68043600 488 # 489 490The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values 491are scaled (shifted) versions of that same value. Note that the min value 492is not at this point in time used in any meaningful way, but the triplet is 493preserved in order to be consistent with things like tcp_rmem. 494 495named_timeout 496------------- 497 498TIPC name table updates are distributed asynchronously in a cluster, without 499any form of transaction handling. This means that different race scenarios are 500possible. One such is that a name withdrawal sent out by one node and received 501by another node may arrive after a second, overlapping name publication already 502has been accepted from a third node, although the conflicting updates 503originally may have been issued in the correct sequential order. 504If named_timeout is nonzero, failed topology updates will be placed on a defer 505queue until another event arrives that clears the error, or until the timeout 506expires. Value is in milliseconds. 507