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Documentation / sysctl / net.txt


Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 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	  - arm32
50	  - ppc64
51	  - sparc64
52	  - mips64
53	  - s390x
54	
55	And the older cBPF JIT supported on the following archs:
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. For drivers that support LRO or GRO_HW, a hardware
99	aggregated packet is counted as one packet in this context.
100	
101	Default: 64
102	
103	dev_weight_rx_bias
104	--------------
105	
106	RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
107	of the driver for the per softirq cycle netdev_budget. This parameter influences
108	the proportion of the configured netdev_budget that is spent on RPS based packet
109	processing during RX softirq cycles. It is further meant for making current
110	dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack.
111	(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based
112	on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias).
113	Default: 1
114	
115	dev_weight_tx_bias
116	--------------
117	
118	Scales the maximum number of packets that can be processed during a TX softirq cycle.
119	Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric
120	net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog.
121	Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias).
122	Default: 1
123	
124	default_qdisc
125	--------------
126	
127	The default queuing discipline to use for network devices. This allows
128	overriding the default of pfifo_fast with an alternative. Since the default
129	queuing discipline is created without additional parameters so is best suited
130	to queuing disciplines that work well without configuration like stochastic
131	fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use
132	queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin
133	which require setting up classes and bandwidths. Note that physical multiqueue
134	interfaces still use mq as root qdisc, which in turn uses this default for its
135	leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead
136	default to noqueue.
137	Default: pfifo_fast
138	
139	busy_read
140	----------------
141	Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL)
142	Approximate time in us to busy loop waiting for packets on the device queue.
143	This sets the default value of the SO_BUSY_POLL socket option.
144	Can be set or overridden per socket by setting socket option SO_BUSY_POLL,
145	which is the preferred method of enabling. If you need to enable the feature
146	globally via sysctl, a value of 50 is recommended.
147	Will increase power usage.
148	Default: 0 (off)
149	
150	busy_poll
151	----------------
152	Low latency busy poll timeout for poll and select. (needs CONFIG_NET_RX_BUSY_POLL)
153	Approximate time in us to busy loop waiting for events.
154	Recommended value depends on the number of sockets you poll on.
155	For several sockets 50, for several hundreds 100.
156	For more than that you probably want to use epoll.
157	Note that only sockets with SO_BUSY_POLL set will be busy polled,
158	so you want to either selectively set SO_BUSY_POLL on those sockets or set
159	sysctl.net.busy_read globally.
160	Will increase power usage.
161	Default: 0 (off)
162	
163	rmem_default
164	------------
165	
166	The default setting of the socket receive buffer in bytes.
167	
168	rmem_max
169	--------
170	
171	The maximum receive socket buffer size in bytes.
172	
173	tstamp_allow_data
174	-----------------
175	Allow processes to receive tx timestamps looped together with the original
176	packet contents. If disabled, transmit timestamp requests from unprivileged
177	processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
178	Default: 1 (on)
179	
180	
181	wmem_default
182	------------
183	
184	The default setting (in bytes) of the socket send buffer.
185	
186	wmem_max
187	--------
188	
189	The maximum send socket buffer size in bytes.
190	
191	message_burst and message_cost
192	------------------------------
193	
194	These parameters  are used to limit the warning messages written to the kernel
195	log from  the  networking  code.  They  enforce  a  rate  limit  to  make  a
196	denial-of-service attack  impossible. A higher message_cost factor, results in
197	fewer messages that will be written. Message_burst controls when messages will
198	be dropped.  The  default  settings  limit  warning messages to one every five
199	seconds.
200	
201	warnings
202	--------
203	
204	This sysctl is now unused.
205	
206	This was used to control console messages from the networking stack that
207	occur because of problems on the network like duplicate address or bad
208	checksums.
209	
210	These messages are now emitted at KERN_DEBUG and can generally be enabled
211	and controlled by the dynamic_debug facility.
212	
213	netdev_budget
214	-------------
215	
216	Maximum number of packets taken from all interfaces in one polling cycle (NAPI
217	poll). In one polling cycle interfaces which are registered to polling are
218	probed in a round-robin manner. Also, a polling cycle may not exceed
219	netdev_budget_usecs microseconds, even if netdev_budget has not been
220	exhausted.
221	
222	netdev_budget_usecs
223	---------------------
224	
225	Maximum number of microseconds in one NAPI polling cycle. Polling
226	will exit when either netdev_budget_usecs have elapsed during the
227	poll cycle or the number of packets processed reaches netdev_budget.
228	
229	netdev_max_backlog
230	------------------
231	
232	Maximum number  of  packets,  queued  on  the  INPUT  side, when the interface
233	receives packets faster than kernel can process them.
234	
235	netdev_rss_key
236	--------------
237	
238	RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is
239	randomly generated.
240	Some user space might need to gather its content even if drivers do not
241	provide ethtool -x support yet.
242	
243	myhost:~# cat /proc/sys/net/core/netdev_rss_key
244	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)
245	
246	File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
247	Note:
248	/proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
249	but most drivers only use 40 bytes of it.
250	
251	myhost:~# ethtool -x eth0
252	RX flow hash indirection table for eth0 with 8 RX ring(s):
253	    0:    0     1     2     3     4     5     6     7
254	RSS hash key:
255	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
256	
257	netdev_tstamp_prequeue
258	----------------------
259	
260	If set to 0, RX packet timestamps can be sampled after RPS processing, when
261	the target CPU processes packets. It might give some delay on timestamps, but
262	permit to distribute the load on several cpus.
263	
264	If set to 1 (default), timestamps are sampled as soon as possible, before
265	queueing.
266	
267	optmem_max
268	----------
269	
270	Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
271	of struct cmsghdr structures with appended data.
272	
273	2. /proc/sys/net/unix - Parameters for Unix domain sockets
274	-------------------------------------------------------
275	
276	There is only one file in this directory.
277	unix_dgram_qlen limits the max number of datagrams queued in Unix domain
278	socket's buffer. It will not take effect unless PF_UNIX flag is specified.
279	
280	
281	3. /proc/sys/net/ipv4 - IPV4 settings
282	-------------------------------------------------------
283	Please see: Documentation/networking/ip-sysctl.txt and ipvs-sysctl.txt for
284	descriptions of these entries.
285	
286	
287	4. Appletalk
288	-------------------------------------------------------
289	
290	The /proc/sys/net/appletalk  directory  holds the Appletalk configuration data
291	when Appletalk is loaded. The configurable parameters are:
292	
293	aarp-expiry-time
294	----------------
295	
296	The amount  of  time  we keep an ARP entry before expiring it. Used to age out
297	old hosts.
298	
299	aarp-resolve-time
300	-----------------
301	
302	The amount of time we will spend trying to resolve an Appletalk address.
303	
304	aarp-retransmit-limit
305	---------------------
306	
307	The number of times we will retransmit a query before giving up.
308	
309	aarp-tick-time
310	--------------
311	
312	Controls the rate at which expires are checked.
313	
314	The directory  /proc/net/appletalk  holds the list of active Appletalk sockets
315	on a machine.
316	
317	The fields  indicate  the DDP type, the local address (in network:node format)
318	the remote  address,  the  size of the transmit pending queue, the size of the
319	received queue  (bytes waiting for applications to read) the state and the uid
320	owning the socket.
321	
322	/proc/net/atalk_iface lists  all  the  interfaces  configured for appletalk.It
323	shows the  name  of the interface, its Appletalk address, the network range on
324	that address  (or  network number for phase 1 networks), and the status of the
325	interface.
326	
327	/proc/net/atalk_route lists  each  known  network  route.  It lists the target
328	(network) that the route leads to, the router (may be directly connected), the
329	route flags, and the device the route is using.
330	
331	
332	5. IPX
333	-------------------------------------------------------
334	
335	The IPX protocol has no tunable values in proc/sys/net.
336	
337	The IPX  protocol  does,  however,  provide  proc/net/ipx. This lists each IPX
338	socket giving  the  local  and  remote  addresses  in  Novell  format (that is
339	network:node:port). In  accordance  with  the  strange  Novell  tradition,
340	everything but the port is in hex. Not_Connected is displayed for sockets that
341	are not  tied to a specific remote address. The Tx and Rx queue sizes indicate
342	the number  of  bytes  pending  for  transmission  and  reception.  The  state
343	indicates the  state  the  socket  is  in and the uid is the owning uid of the
344	socket.
345	
346	The /proc/net/ipx_interface  file lists all IPX interfaces. For each interface
347	it gives  the network number, the node number, and indicates if the network is
348	the primary  network.  It  also  indicates  which  device  it  is bound to (or
349	Internal for  internal  networks)  and  the  Frame  Type if appropriate. Linux
350	supports 802.3,  802.2,  802.2  SNAP  and DIX (Blue Book) ethernet framing for
351	IPX.
352	
353	The /proc/net/ipx_route  table  holds  a list of IPX routes. For each route it
354	gives the  destination  network, the router node (or Directly) and the network
355	address of the router (or Connected) for internal networks.
356	
357	6. TIPC
358	-------------------------------------------------------
359	
360	tipc_rmem
361	----------
362	
363	The TIPC protocol now has a tunable for the receive memory, similar to the
364	tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max)
365	
366	    # cat /proc/sys/net/tipc/tipc_rmem
367	    4252725 34021800        68043600
368	    #
369	
370	The max value is set to CONN_OVERLOAD_LIMIT, and the default and min values
371	are scaled (shifted) versions of that same value.  Note that the min value
372	is not at this point in time used in any meaningful way, but the triplet is
373	preserved in order to be consistent with things like tcp_rmem.
374	
375	named_timeout
376	--------------
377	
378	TIPC name table updates are distributed asynchronously in a cluster, without
379	any form of transaction handling. This means that different race scenarios are
380	possible. One such is that a name withdrawal sent out by one node and received
381	by another node may arrive after a second, overlapping name publication already
382	has been accepted from a third node, although the conflicting updates
383	originally may have been issued in the correct sequential order.
384	If named_timeout is nonzero, failed topology updates will be placed on a defer
385	queue until another event arrives that clears the error, or until the timeout
386	expires. Value is in milliseconds.
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