================================Documentation for /proc/sys/net/================================ Copyright Copyright (c) 1999 	- Terrehon Bowden <terrehon@pacbell.net>	- Bodo Bauer <bb@ricochet.net> Copyright (c) 2000 	- Jorge Nerin <comandante@zaralinux.com> Copyright (c) 2009 	- Shen Feng <shen@cn.fujitsu.com> For general info and legal blurb, please look in index.rst. ------------------------------------------------------------------------------ This file contains the documentation for the sysctl files in/proc/sys/net The interface  to  the  networking  parts  of  the  kernel  is  located  in/proc/sys/net. The following table shows all possible subdirectories.  You maysee only some of them, depending on your kernel's configuration.  Table : Subdirectories in /proc/sys/net  ========= =================== = ========== =================== Directory Content               Directory  Content ========= =================== = ========== =================== 802       E802 protocol         mptcp      Multipath TCP appletalk Appletalk protocol    netfilter  Network Filter bridge    Bridging              tipc       TIPC core      General parameter     unix       Unix domain sockets ethernet  Ethernet protocol     vsock      VSOCK sockets ipv4      IP version 4          x25        X.25 protocol ipv6      IP version 6 ========= =================== = ========== =================== 1. /proc/sys/net/core - Network core options============================================ bpf_jit_enable-------------- This enables the BPF Just in Time (JIT) compiler. BPF is a flexibleand efficient infrastructure allowing to execute bytecode at varioushook points. It is used in a number of Linux kernel subsystems suchas networking (e.g. XDP, tc), tracing (e.g. kprobes, uprobes, tracepoints)and security (e.g. seccomp). LLVM has a BPF back end that can compilerestricted C into a sequence of BPF instructions. After program loadthrough bpf(2) and passing a verifier in the kernel, a JIT will thentranslate these BPF proglets into native CPU instructions. There aretwo flavors of JITs, the newer eBPF JIT currently supported on:   - x86_64  - x86_32  - arm64  - arm32  - ppc64  - ppc32  - sparc64  - mips64  - s390x  - riscv64  - riscv32  - loongarch64  - arc And the older cBPF JIT supported on the following archs:   - mips  - sparc eBPF JITs are a superset of cBPF JITs, meaning the kernel willmigrate cBPF instructions into eBPF instructions and then JITcompile them transparently. Older cBPF JITs can only translatetcpdump filters, seccomp rules, etc, but not mentioned eBPFprograms loaded through bpf(2). Values: 	- 0 - disable the JIT (default value)	- 1 - enable the JIT	- 2 - enable the JIT and ask the compiler to emit traces on kernel log. bpf_jit_harden-------------- This enables hardening for the BPF JIT compiler. Supported are eBPFJIT backends. Enabling hardening trades off performance, but canmitigate JIT spraying. Values: 	- 0 - disable JIT hardening (default value)	- 1 - enable JIT hardening for unprivileged users only	- 2 - enable JIT hardening for all users where "privileged user" in this context means a process havingCAP_BPF or CAP_SYS_ADMIN in the root user name space. bpf_jit_kallsyms---------------- When BPF JIT compiler is enabled, then compiled images are unknownaddresses to the kernel, meaning they neither show up in traces norin /proc/kallsyms. This enables export of these addresses, which canbe used for debugging/tracing. If bpf_jit_harden is enabled, thisfeature is disabled. Values : 	- 0 - disable JIT kallsyms export (default value)	- 1 - enable JIT kallsyms export for privileged users only bpf_jit_limit------------- This enforces a global limit for memory allocations to the BPF JITcompiler in order to reject unprivileged JIT requests once it hasbeen surpassed. bpf_jit_limit contains the value of the global limitin bytes. dev_weight---------- The maximum number of packets that kernel can handle on a NAPI interrupt,it's a Per-CPU variable. For drivers that support LRO or GRO_HW, a hardwareaggregated packet is counted as one packet in this context. Default: 64 dev_weight_rx_bias------------------ RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll functionof the driver for the per softirq cycle netdev_budget. This parameter influencesthe proportion of the configured netdev_budget that is spent on RPS based packetprocessing during RX softirq cycles. It is further meant for making currentdev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack.(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is basedon dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias). Default: 1 dev_weight_tx_bias------------------ Scales the maximum number of packets that can be processed during a TX softirq cycle.Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetricnet stack processing needs. Be careful to avoid making TX softirq processing a CPU hog. Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias). Default: 1 default_qdisc------------- The default queuing discipline to use for network devices. This allowsoverriding the default of pfifo_fast with an alternative. Since the defaultqueuing discipline is created without additional parameters so is best suitedto queuing disciplines that work well without configuration like stochasticfair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't usequeuing disciplines like Hierarchical Token Bucket or Deficit Round Robinwhich require setting up classes and bandwidths. Note that physical multiqueueinterfaces still use mq as root qdisc, which in turn uses this default for itsleaves. Virtual devices (like e.g. lo or veth) ignore this setting and insteaddefault to noqueue. Default: pfifo_fast busy_read--------- Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL)Approximate time in us to busy loop waiting for packets on the device queue.This sets the default value of the SO_BUSY_POLL socket option.Can be set or overridden per socket by setting socket option SO_BUSY_POLL,which is the preferred method of enabling. If you need to enable the featureglobally via sysctl, a value of 50 is recommended. Will increase power usage. Default: 0 (off) busy_poll----------------Low latency busy poll timeout for poll and select. (needs CONFIG_NET_RX_BUSY_POLL)Approximate time in us to busy loop waiting for events.Recommended value depends on the number of sockets you poll on.For several sockets 50, for several hundreds 100.For more than that you probably want to use epoll.Note that only sockets with SO_BUSY_POLL set will be busy polled,so you want to either selectively set SO_BUSY_POLL on those sockets or setsysctl.net.busy_read globally. Will increase power usage. Default: 0 (off) mem_pcpu_rsv------------ Per-cpu reserved forward alloc cache size in page units. Default 1MB per CPU. bypass_prot_mem--------------- Skip charging socket buffers to the global per-protocol memoryaccounting controlled by net.ipv4.tcp_mem, net.ipv4.udp_mem, etc. Default: 0 (off) rmem_default------------ The default setting of the socket receive buffer in bytes. rmem_max-------- The maximum receive socket buffer size in bytes. Default: 4194304 rps_default_mask---------------- The default RPS CPU mask used on newly created network devices. An emptymask means RPS disabled by default. tstamp_allow_data-----------------Allow processes to receive tx timestamps looped together with the originalpacket contents. If disabled, transmit timestamp requests from unprivilegedprocesses are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set. Default: 1 (on)  wmem_default------------ The default setting (in bytes) of the socket send buffer. wmem_max-------- The maximum send socket buffer size in bytes. Default: 4194304 message_burst and message_cost------------------------------ These parameters  are used to limit the warning messages written to the kernellog from  the  networking  code.  They  enforce  a  rate  limit  to  make  adenial-of-service attack  impossible. A higher message_cost factor, results infewer messages that will be written. Message_burst controls when messages willbe dropped.  The  default  settings  limit  warning messages to one every fiveseconds. warnings-------- This sysctl is now unused. This was used to control console messages from the networking stack thatoccur because of problems on the network like duplicate address or badchecksums. These messages are now emitted at KERN_DEBUG and can generally be enabledand controlled by the dynamic_debug facility. netdev_budget------------- Maximum number of packets taken from all interfaces in one polling cycle (NAPIpoll). In one polling cycle interfaces which are registered to polling areprobed in a round-robin manner. Also, a polling cycle may not exceednetdev_budget_usecs microseconds, even if netdev_budget has not beenexhausted. netdev_budget_usecs--------------------- Maximum number of microseconds in one NAPI polling cycle. Pollingwill exit when either netdev_budget_usecs have elapsed during thepoll cycle or the number of packets processed reaches netdev_budget. netdev_max_backlog------------------ Maximum number of packets, queued on the INPUT side, when the interfacereceives packets faster than kernel can process them. qdisc_max_burst------------------ Maximum number of packets that can be temporarily stored beforereaching qdisc. Default: 1000 netdev_rss_key-------------- RSS (Receive Side Scaling) enabled drivers use a host key thatis randomly generated.Some user space might need to gather its content even if drivers do notprovide ethtool -x support yet. ::   myhost:~# cat /proc/sys/net/core/netdev_rss_key  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: ... (256 bytes total) File contains all nul bytes if no driver ever called netdev_rss_key_fill()function. Note:  /proc/sys/net/core/netdev_rss_key contains 256 bytes of key,  but many drivers only use 40 or 52 bytes of it. ::   myhost:~# ethtool -x eth0  RX flow hash indirection table for eth0 with 8 RX ring(s):      0:    0     1     2     3     4     5     6     7  RSS hash key:  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 netdev_tstamp_prequeue---------------------- If set to 0, RX packet timestamps can be sampled after RPS processing, whenthe target CPU processes packets. It might give some delay on timestamps, butpermit to distribute the load on several cpus. If set to 1 (default), timestamps are sampled as soon as possible, beforequeueing. netdev_unregister_timeout_secs------------------------------ Unregister network device timeout in seconds.This option controls the timeout (in seconds) used to issue a warning whilewaiting for a network device refcount to drop to 0 during deviceunregistration. A lower value may be useful during bisection to detecta leaked reference faster. A larger value may be useful to prevent falsewarnings on slow/loaded systems.Default value is 10, minimum 1, maximum 3600. skb_defer_max------------- Max size (in skbs) of the per-cpu list of skbs being freedby the cpu which allocated them. Default: 128 optmem_max---------- Maximum ancillary buffer size allowed per socket. Ancillary data is a sequenceof struct cmsghdr structures with appended data. TCP tx zerocopy also usesoptmem_max as a limit for its internal structures. Default : 128 KB fb_tunnels_only_for_init_net---------------------------- Controls if fallback tunnels (like tunl0, gre0, gretap0, erspan0,sit0, ip6tnl0, ip6gre0) are automatically created. There are 3 possibilities(a) value = 0; respective fallback tunnels are created when module isloaded in every net namespaces (backward compatible behavior).(b) value = 1; [kcmd value: initns] respective fallback tunnels arecreated only in init net namespace and every other net namespace willnot have them.(c) value = 2; [kcmd value: none] fallback tunnels are not createdwhen a module is loaded in any of the net namespace. Setting value to"2" is pointless after boot if these modules are built-in, so there isa kernel command-line option that can change this default. Please refer toDocumentation/admin-guide/kernel-parameters.txt for additional details. Not creating fallback tunnels gives control to userspace to createwhatever is needed only and avoid creating devices which are redundant. Default : 0  (for compatibility reasons) devconf_inherit_init_net------------------------ Controls if a new network namespace should inherit all currentsettings under /proc/sys/net/{ipv4,ipv6}/conf/{all,default}/. Bydefault, we keep the current behavior: for IPv4 we inherit all currentsettings from init_net and for IPv6 we reset all settings to default. If set to 1, both IPv4 and IPv6 settings are forced to inherit fromcurrent ones in init_net. If set to 2, both IPv4 and IPv6 settings areforced to reset to their default values. If set to 3, both IPv4 and IPv6settings are forced to inherit from current ones in the netns where thisnew netns has been created. Default : 0  (for compatibility reasons) txrehash-------- Controls default hash rethink behaviour on socket when SO_TXREHASH option is setto SOCK_TXREHASH_DEFAULT (i. e. not overridden by setsockopt). If set to 1 (default), hash rethink is performed on listening socket.If set to 0, hash rethink is not performed. txq_reselection_ms------------------ Controls how often (in ms) a busy connected flow can select another tx queue. A resection is desirable when/if user thread has migrated and XPSwould select a different queue. Same can occur without XPSif the flow hash has changed. But switching txq can introduce reorders, especially if theold queue is under high pressure. Modern TCP stacks dealwell with reorders if they happen not too often. To disable this feature, set the value to 0. Default : 1000 gro_normal_batch---------------- Maximum number of the segments to batch up on output of GRO. When a packetexits GRO, either as a coalesced superframe or as an original packet whichGRO has decided not to coalesce, it is placed on a per-NAPI list. Thislist is then passed to the stack when the number of segments reaches thegro_normal_batch limit. high_order_alloc_disable------------------------ By default the allocator for page frags tries to use high order pages (order-3on x86). While the default behavior gives good results in most cases, some usersmight have hit a contention in page allocations/freeing. This was especiallytrue on older kernels (< 5.14) when high-order pages were not stored on per-cpulists. This allows to opt-in for order-0 allocation instead but is now mostly ofhistorical importance. Default: 0 2. /proc/sys/net/unix - Parameters for Unix domain sockets---------------------------------------------------------- There is only one file in this directory.unix_dgram_qlen limits the max number of datagrams queued in Unix domainsocket's buffer. It will not take effect unless PF_UNIX flag is specified.  3. /proc/sys/net/ipv4 - IPV4 settings-------------------------------------Please see: Documentation/networking/ip-sysctl.rst andDocumentation/admin-guide/sysctl/net.rst for descriptions of these entries.  4. TIPC------- tipc_rmem--------- The TIPC protocol now has a tunable for the receive memory, similar to thetcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max) ::     # cat /proc/sys/net/tipc/tipc_rmem    4252725 34021800        68043600    # The max value is set to CONN_OVERLOAD_LIMIT, and the default and min valuesare scaled (shifted) versions of that same value.  Note that the min valueis not at this point in time used in any meaningful way, but the triplet ispreserved in order to be consistent with things like tcp_rmem. named_timeout------------- TIPC name table updates are distributed asynchronously in a cluster, without

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