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