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Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 EST.

1	Documentation for /proc/sys/net/*
2		(c) 1999		Terrehon Bowden <terrehon@pacbell.net>
3					Bodo Bauer <bb@ricochet.net>
4		(c) 2000		Jorge Nerin <comandante@zaralinux.com>
5		(c) 2009		Shen Feng <shen@cn.fujitsu.com>
6	
7	For general info and legal blurb, please look in README.
8	
9	==============================================================
10	
11	This file contains the documentation for the sysctl files in
12	/proc/sys/net
13	
14	The interface  to  the  networking  parts  of  the  kernel  is  located  in
15	/proc/sys/net. The following table shows all possible subdirectories.  You may
16	see only some of them, depending on your kernel's configuration.
17	
18	
19	Table : Subdirectories in /proc/sys/net
20	..............................................................................
21	 Directory Content             Directory  Content
22	 core      General parameter   appletalk  Appletalk protocol
23	 unix      Unix domain sockets netrom     NET/ROM
24	 802       E802 protocol       ax25       AX25
25	 ethernet  Ethernet protocol   rose       X.25 PLP layer
26	 ipv4      IP version 4        x25        X.25 protocol
27	 ipx       IPX                 token-ring IBM token ring
28	 bridge    Bridging            decnet     DEC net
29	 ipv6      IP version 6        tipc       TIPC
30	..............................................................................
31	
32	1. /proc/sys/net/core - Network core options
33	-------------------------------------------------------
34	
35	bpf_jit_enable
36	--------------
37	
38	This enables the BPF Just in Time (JIT) compiler. BPF is a flexible
39	and efficient infrastructure allowing to execute bytecode at various
40	hook points. It is used in a number of Linux kernel subsystems such
41	as networking (e.g. XDP, tc), tracing (e.g. kprobes, uprobes, tracepoints)
42	and security (e.g. seccomp). LLVM has a BPF back end that can compile
43	restricted C into a sequence of BPF instructions. After program load
44	through bpf(2) and passing a verifier in the kernel, a JIT will then
45	translate these BPF proglets into native CPU instructions. There are
46	two flavors of JITs, the newer eBPF JIT currently supported on:
47	  - x86_64
48	  - arm64
49	  - ppc64
50	  - sparc64
51	  - mips64
52	  - s390x
53	
54	And the older cBPF JIT supported on the following archs:
55	  - arm
56	  - mips
57	  - ppc
58	  - sparc
59	
60	eBPF JITs are a superset of cBPF JITs, meaning the kernel will
61	migrate cBPF instructions into eBPF instructions and then JIT
62	compile them transparently. Older cBPF JITs can only translate
63	tcpdump filters, seccomp rules, etc, but not mentioned eBPF
64	programs loaded through bpf(2).
65	
66	Values :
67		0 - disable the JIT (default value)
68		1 - enable the JIT
69		2 - enable the JIT and ask the compiler to emit traces on kernel log.
70	
71	bpf_jit_harden
72	--------------
73	
74	This enables hardening for the BPF JIT compiler. Supported are eBPF
75	JIT backends. Enabling hardening trades off performance, but can
76	mitigate JIT spraying.
77	Values :
78		0 - disable JIT hardening (default value)
79		1 - enable JIT hardening for unprivileged users only
80		2 - enable JIT hardening for all users
81	
82	bpf_jit_kallsyms
83	----------------
84	
85	When BPF JIT compiler is enabled, then compiled images are unknown
86	addresses to the kernel, meaning they neither show up in traces nor
87	in /proc/kallsyms. This enables export of these addresses, which can
88	be used for debugging/tracing. If bpf_jit_harden is enabled, this
89	feature is disabled.
90	Values :
91		0 - disable JIT kallsyms export (default value)
92		1 - enable JIT kallsyms export for privileged users only
93	
94	dev_weight
95	--------------
96	
97	The maximum number of packets that kernel can handle on a NAPI interrupt,
98	it's a Per-CPU variable.
99	Default: 64
100	
101	dev_weight_rx_bias
102	--------------
103	
104	RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
105	of the driver for the per softirq cycle netdev_budget. This parameter influences
106	the proportion of the configured netdev_budget that is spent on RPS based packet
107	processing during RX softirq cycles. It is further meant for making current
108	dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack.
109	(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based
110	on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias).
111	Default: 1
112	
113	dev_weight_tx_bias
114	--------------
115	
116	Scales the maximum number of packets that can be processed during a TX softirq cycle.
117	Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric
118	net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog.
119	Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias).
120	Default: 1
121	
122	default_qdisc
123	--------------
124	
125	The default queuing discipline to use for network devices. This allows
126	overriding the default of pfifo_fast with an alternative. Since the default
127	queuing discipline is created without additional parameters so is best suited
128	to queuing disciplines that work well without configuration like stochastic
129	fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use
130	queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin
131	which require setting up classes and bandwidths. Note that physical multiqueue
132	interfaces still use mq as root qdisc, which in turn uses this default for its
133	leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead
134	default to noqueue.
135	Default: pfifo_fast
136	
137	busy_read
138	----------------
139	Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL)
140	Approximate time in us to busy loop waiting for packets on the device queue.
141	This sets the default value of the SO_BUSY_POLL socket option.
142	Can be set or overridden per socket by setting socket option SO_BUSY_POLL,
143	which is the preferred method of enabling. If you need to enable the feature
144	globally via sysctl, a value of 50 is recommended.
145	Will increase power usage.
146	Default: 0 (off)
147	
148	busy_poll
149	----------------
150	Low latency busy poll timeout for poll and select. (needs CONFIG_NET_RX_BUSY_POLL)
151	Approximate time in us to busy loop waiting for events.
152	Recommended value depends on the number of sockets you poll on.
153	For several sockets 50, for several hundreds 100.
154	For more than that you probably want to use epoll.
155	Note that only sockets with SO_BUSY_POLL set will be busy polled,
156	so you want to either selectively set SO_BUSY_POLL on those sockets or set
157	sysctl.net.busy_read globally.
158	Will increase power usage.
159	Default: 0 (off)
160	
161	rmem_default
162	------------
163	
164	The default setting of the socket receive buffer in bytes.
165	
166	rmem_max
167	--------
168	
169	The maximum receive socket buffer size in bytes.
170	
171	tstamp_allow_data
172	-----------------
173	Allow processes to receive tx timestamps looped together with the original
174	packet contents. If disabled, transmit timestamp requests from unprivileged
175	processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
176	Default: 1 (on)
177	
178	
179	wmem_default
180	------------
181	
182	The default setting (in bytes) of the socket send buffer.
183	
184	wmem_max
185	--------
186	
187	The maximum send socket buffer size in bytes.
188	
189	message_burst and message_cost
190	------------------------------
191	
192	These parameters  are used to limit the warning messages written to the kernel
193	log from  the  networking  code.  They  enforce  a  rate  limit  to  make  a
194	denial-of-service attack  impossible. A higher message_cost factor, results in
195	fewer messages that will be written. Message_burst controls when messages will
196	be dropped.  The  default  settings  limit  warning messages to one every five
197	seconds.
198	
199	warnings
200	--------
201	
202	This sysctl is now unused.
203	
204	This was used to control console messages from the networking stack that
205	occur because of problems on the network like duplicate address or bad
206	checksums.
207	
208	These messages are now emitted at KERN_DEBUG and can generally be enabled
209	and controlled by the dynamic_debug facility.
210	
211	netdev_budget
212	-------------
213	
214	Maximum number of packets taken from all interfaces in one polling cycle (NAPI
215	poll). In one polling cycle interfaces which are registered to polling are
216	probed in a round-robin manner. Also, a polling cycle may not exceed
217	netdev_budget_usecs microseconds, even if netdev_budget has not been
218	exhausted.
219	
220	netdev_budget_usecs
221	---------------------
222	
223	Maximum number of microseconds in one NAPI polling cycle. Polling
224	will exit when either netdev_budget_usecs have elapsed during the
225	poll cycle or the number of packets processed reaches netdev_budget.
226	
227	netdev_max_backlog
228	------------------
229	
230	Maximum number  of  packets,  queued  on  the  INPUT  side, when the interface
231	receives packets faster than kernel can process them.
232	
233	netdev_rss_key
234	--------------
235	
236	RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is
237	randomly generated.
238	Some user space might need to gather its content even if drivers do not
239	provide ethtool -x support yet.
240	
241	myhost:~# cat /proc/sys/net/core/netdev_rss_key
242	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)
243	
244	File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
245	Note:
246	/proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
247	but most drivers only use 40 bytes of it.
248	
249	myhost:~# ethtool -x eth0
250	RX flow hash indirection table for eth0 with 8 RX ring(s):
251	    0:    0     1     2     3     4     5     6     7
252	RSS hash key:
253	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
254	
255	netdev_tstamp_prequeue
256	----------------------
257	
258	If set to 0, RX packet timestamps can be sampled after RPS processing, when
259	the target CPU processes packets. It might give some delay on timestamps, but
260	permit to distribute the load on several cpus.
261	
262	If set to 1 (default), timestamps are sampled as soon as possible, before
263	queueing.
264	
265	optmem_max
266	----------
267	
268	Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
269	of struct cmsghdr structures with appended data.
270	
271	2. /proc/sys/net/unix - Parameters for Unix domain sockets
272	-------------------------------------------------------
273	
274	There is only one file in this directory.
275	unix_dgram_qlen limits the max number of datagrams queued in Unix domain
276	socket's buffer. It will not take effect unless PF_UNIX flag is specified.
277	
278	
279	3. /proc/sys/net/ipv4 - IPV4 settings
280	-------------------------------------------------------
281	Please see: Documentation/networking/ip-sysctl.txt and ipvs-sysctl.txt for
282	descriptions of these entries.
283	
284	
285	4. Appletalk
286	-------------------------------------------------------
287	
288	The /proc/sys/net/appletalk  directory  holds the Appletalk configuration data
289	when Appletalk is loaded. The configurable parameters are:
290	
291	aarp-expiry-time
292	----------------
293	
294	The amount  of  time  we keep an ARP entry before expiring it. Used to age out
295	old hosts.
296	
297	aarp-resolve-time
298	-----------------
299	
300	The amount of time we will spend trying to resolve an Appletalk address.
301	
302	aarp-retransmit-limit
303	---------------------
304	
305	The number of times we will retransmit a query before giving up.
306	
307	aarp-tick-time
308	--------------
309	
310	Controls the rate at which expires are checked.
311	
312	The directory  /proc/net/appletalk  holds the list of active Appletalk sockets
313	on a machine.
314	
315	The fields  indicate  the DDP type, the local address (in network:node format)
316	the remote  address,  the  size of the transmit pending queue, the size of the
317	received queue  (bytes waiting for applications to read) the state and the uid
318	owning the socket.
319	
320	/proc/net/atalk_iface lists  all  the  interfaces  configured for appletalk.It
321	shows the  name  of the interface, its Appletalk address, the network range on
322	that address  (or  network number for phase 1 networks), and the status of the
323	interface.
324	
325	/proc/net/atalk_route lists  each  known  network  route.  It lists the target
326	(network) that the route leads to, the router (may be directly connected), the
327	route flags, and the device the route is using.
328	
329	
330	5. IPX
331	-------------------------------------------------------
332	
333	The IPX protocol has no tunable values in proc/sys/net.
334	
335	The IPX  protocol  does,  however,  provide  proc/net/ipx. This lists each IPX
336	socket giving  the  local  and  remote  addresses  in  Novell  format (that is
337	network:node:port). In  accordance  with  the  strange  Novell  tradition,
338	everything but the port is in hex. Not_Connected is displayed for sockets that
339	are not  tied to a specific remote address. The Tx and Rx queue sizes indicate
340	the number  of  bytes  pending  for  transmission  and  reception.  The  state
341	indicates the  state  the  socket  is  in and the uid is the owning uid of the
342	socket.
343	
344	The /proc/net/ipx_interface  file lists all IPX interfaces. For each interface
345	it gives  the network number, the node number, and indicates if the network is
346	the primary  network.  It  also  indicates  which  device  it  is bound to (or
347	Internal for  internal  networks)  and  the  Frame  Type if appropriate. Linux
348	supports 802.3,  802.2,  802.2  SNAP  and DIX (Blue Book) ethernet framing for
349	IPX.
350	
351	The /proc/net/ipx_route  table  holds  a list of IPX routes. For each route it
352	gives the  destination  network, the router node (or Directly) and the network
353	address of the router (or Connected) for internal networks.
354	
355	6. TIPC
356	-------------------------------------------------------
357	
358	tipc_rmem
359	----------
360	
361	The TIPC protocol now has a tunable for the receive memory, similar to the
362	tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max)
363	
364	    # cat /proc/sys/net/tipc/tipc_rmem
365	    4252725 34021800        68043600
366	    #
367	
368	The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values
369	are scaled (shifted) versions of that same value.  Note that the min value
370	is not at this point in time used in any meaningful way, but the triplet is
371	preserved in order to be consistent with things like tcp_rmem.
372	
373	named_timeout
374	--------------
375	
376	TIPC name table updates are distributed asynchronously in a cluster, without
377	any form of transaction handling. This means that different race scenarios are
378	possible. One such is that a name withdrawal sent out by one node and received
379	by another node may arrive after a second, overlapping name publication already
380	has been accepted from a third node, although the conflicting updates
381	originally may have been issued in the correct sequential order.
382	If named_timeout is nonzero, failed topology updates will be placed on a defer
383	queue until another event arrives that clears the error, or until the timeout
384	expires. Value is in milliseconds.
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