Documentation/sysctl/net.txt - kernel/msm-5.4 - Gitiles

 Documentation for /proc/sys/net/*
 	(c) 1999		Terrehon Bowden <terrehon@pacbell.net>
 				Bodo Bauer <bb@ricochet.net>
 	(c) 2000		Jorge Nerin <comandante@zaralinux.com>
 	(c) 2009		Shen Feng <shen@cn.fujitsu.com>

 For general info and legal blurb, please look in README.

 ==============================================================

 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 may
 see only some of them, depending on your kernel's configuration.


 Table : Subdirectories in /proc/sys/net
 ..............................................................................
  Directory Content             Directory  Content
  core      General parameter   appletalk  Appletalk protocol
  unix      Unix domain sockets netrom     NET/ROM
  802       E802 protocol       ax25       AX25
  ethernet  Ethernet protocol   rose       X.25 PLP layer
  ipv4      IP version 4        x25        X.25 protocol
  ipx       IPX                 token-ring IBM token ring
  bridge    Bridging            decnet     DEC net
  ipv6      IP version 6        tipc       TIPC
 ..............................................................................

 1. /proc/sys/net/core - Network core options
 -------------------------------------------------------

 bpf_jit_enable
 --------------

 This enables Berkeley Packet Filter Just in Time compiler.
 Currently supported on x86_64 architecture, bpf_jit provides a framework
 to speed packet filtering, the one used by tcpdump/libpcap for example.
 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 Berkeley Packet Filter Just in Time compiler.
 Supported are eBPF JIT backends. Enabling hardening trades off performance,
 but can mitigate JIT spraying.
 Values :
 	0 - disable JIT hardening (default value)
 	1 - enable JIT hardening for unprivileged users only
 	2 - enable JIT hardening for all users

 bpf_jit_kallsyms
 ----------------

 When Berkeley Packet Filter Just in Time compiler is enabled, then compiled
 images are unknown addresses to the kernel, meaning they neither show up in
 traces nor in /proc/kallsyms. This enables export of these addresses, which
 can be used for debugging/tracing. If bpf_jit_harden is enabled, this feature
 is disabled.
 Values :
 	0 - disable JIT kallsyms export (default value)
 	1 - enable JIT kallsyms export for privileged users only

 dev_weight
 --------------

 The maximum number of packets that kernel can handle on a NAPI interrupt,
 it's a Per-CPU variable.
 Default: 64

 dev_weight_rx_bias
 --------------

 RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
 of the driver for the per softirq cycle netdev_budget. This parameter influences
 the proportion of the configured netdev_budget that is spent on RPS based packet
 processing during RX softirq cycles. It is further meant for making current
 dev_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 based
 on 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 asymmetric
 net 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 allows
 overriding the default of pfifo_fast with an alternative. Since the default
 queuing discipline is created without additional parameters so is best suited
 to queuing disciplines that work well without configuration like stochastic
 fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use
 queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin
 which require setting up classes and bandwidths. Note that physical multiqueue
 interfaces still use mq as root qdisc, which in turn uses this default for its
 leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead
 default 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 feature
 globally 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 set
 sysctl.net.busy_read globally.
 Will increase power usage.
 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.

 tstamp_allow_data
 -----------------
 Allow processes to receive tx timestamps looped together with the original
 packet contents. If disabled, transmit timestamp requests from unprivileged
 processes 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.

 message_burst and message_cost
 ------------------------------

 These parameters  are used to limit the warning messages written to the kernel
 log from  the  networking  code.  They  enforce  a  rate  limit  to  make  a
 denial-of-service attack  impossible. A higher message_cost factor, results in
 fewer messages that will be written. Message_burst controls when messages will
 be dropped.  The  default  settings  limit  warning messages to one every five
 seconds.

 warnings
 --------

 This sysctl is now unused.

 This was used to control console messages from the networking stack that
 occur because of problems on the network like duplicate address or bad
 checksums.

 These messages are now emitted at KERN_DEBUG and can generally be enabled
 and controlled by the dynamic_debug facility.

 netdev_budget
 -------------

 Maximum number of packets taken from all interfaces in one polling cycle (NAPI
 poll). In one polling cycle interfaces which are registered to polling are
 probed in a round-robin manner.

 netdev_max_backlog
 ------------------

 Maximum number  of  packets,  queued  on  the  INPUT  side, when the interface
 receives packets faster than kernel can process them.

 netdev_rss_key
 --------------

 RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is
 randomly generated.
 Some user space might need to gather its content even if drivers do not
 provide 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: ... (52 bytes total)

 File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
 Note:
 /proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
 but most drivers only use 40 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, when
 the target CPU processes packets. It might give some delay on timestamps, but
 permit to distribute the load on several cpus.

 If set to 1 (default), timestamps are sampled as soon as possible, before
 queueing.

 optmem_max
 ----------

 Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
 of struct cmsghdr structures with appended data.

 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 domain
 socket'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.txt and ipvs-sysctl.txt for
 descriptions of these entries.


 4. Appletalk
 -------------------------------------------------------

 The /proc/sys/net/appletalk  directory  holds the Appletalk configuration data
 when Appletalk is loaded. The configurable parameters are:

 aarp-expiry-time
 ----------------

 The amount  of  time  we keep an ARP entry before expiring it. Used to age out
 old hosts.

 aarp-resolve-time
 -----------------

 The amount of time we will spend trying to resolve an Appletalk address.

 aarp-retransmit-limit
 ---------------------

 The number of times we will retransmit a query before giving up.

 aarp-tick-time
 --------------

 Controls the rate at which expires are checked.

 The directory  /proc/net/appletalk  holds the list of active Appletalk sockets
 on a machine.

 The fields  indicate  the DDP type, the local address (in network:node format)
 the remote  address,  the  size of the transmit pending queue, the size of the
 received queue  (bytes waiting for applications to read) the state and the uid
 owning the socket.

 /proc/net/atalk_iface lists  all  the  interfaces  configured for appletalk.It
 shows the  name  of the interface, its Appletalk address, the network range on
 that address  (or  network number for phase 1 networks), and the status of the
 interface.

 /proc/net/atalk_route lists  each  known  network  route.  It lists the target
 (network) that the route leads to, the router (may be directly connected), the
 route flags, and the device the route is using.


 5. IPX
 -------------------------------------------------------

 The IPX protocol has no tunable values in proc/sys/net.

 The IPX  protocol  does,  however,  provide  proc/net/ipx. This lists each IPX
 socket giving  the  local  and  remote  addresses  in  Novell  format (that is
 network:node:port). In  accordance  with  the  strange  Novell  tradition,
 everything but the port is in hex. Not_Connected is displayed for sockets that
 are not  tied to a specific remote address. The Tx and Rx queue sizes indicate
 the number  of  bytes  pending  for  transmission  and  reception.  The  state
 indicates the  state  the  socket  is  in and the uid is the owning uid of the
 socket.

 The /proc/net/ipx_interface  file lists all IPX interfaces. For each interface
 it gives  the network number, the node number, and indicates if the network is
 the primary  network.  It  also  indicates  which  device  it  is bound to (or
 Internal for  internal  networks)  and  the  Frame  Type if appropriate. Linux
 supports 802.3,  802.2,  802.2  SNAP  and DIX (Blue Book) ethernet framing for
 IPX.

 The /proc/net/ipx_route  table  holds  a list of IPX routes. For each route it
 gives the  destination  network, the router node (or Directly) and the network
 address of the router (or Connected) for internal networks.

 6. TIPC
 -------------------------------------------------------

 tipc_rmem
 ----------

 The TIPC protocol now has a tunable for the receive memory, similar to the
 tcp_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 values
 are scaled (shifted) versions of that same value.  Note that the min value
 is not at this point in time used in any meaningful way, but the triplet is
 preserved in order to be consistent with things like tcp_rmem.

 named_timeout
 --------------

 TIPC name table updates are distributed asynchronously in a cluster, without
 any form of transaction handling. This means that different race scenarios are
 possible. One such is that a name withdrawal sent out by one node and received
 by another node may arrive after a second, overlapping name publication already
 has been accepted from a third node, although the conflicting updates
 originally may have been issued in the correct sequential order.
 If named_timeout is nonzero, failed topology updates will be placed on a defer
 queue until another event arrives that clears the error, or until the timeout
 expires. Value is in milliseconds.
	Documentation for /proc/sys/net/*
	(c) 1999 Terrehon Bowden <terrehon@pacbell.net>
	Bodo Bauer <bb@ricochet.net>
	(c) 2000 Jorge Nerin <comandante@zaralinux.com>
	(c) 2009 Shen Feng <shen@cn.fujitsu.com>

	For general info and legal blurb, please look in README.

	==============================================================

	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 may
	see only some of them, depending on your kernel's configuration.


	Table : Subdirectories in /proc/sys/net
	..............................................................................
	Directory Content Directory Content
	core General parameter appletalk Appletalk protocol
	unix Unix domain sockets netrom NET/ROM
	802 E802 protocol ax25 AX25
	ethernet Ethernet protocol rose X.25 PLP layer
	ipv4 IP version 4 x25 X.25 protocol
	ipx IPX token-ring IBM token ring
	bridge Bridging decnet DEC net
	ipv6 IP version 6 tipc TIPC
	..............................................................................

	1. /proc/sys/net/core - Network core options
	-------------------------------------------------------

	bpf_jit_enable
	--------------

	This enables Berkeley Packet Filter Just in Time compiler.
	Currently supported on x86_64 architecture, bpf_jit provides a framework
	to speed packet filtering, the one used by tcpdump/libpcap for example.
	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 Berkeley Packet Filter Just in Time compiler.
	Supported are eBPF JIT backends. Enabling hardening trades off performance,
	but can mitigate JIT spraying.
	Values :
	0 - disable JIT hardening (default value)
	1 - enable JIT hardening for unprivileged users only
	2 - enable JIT hardening for all users

	bpf_jit_kallsyms
	----------------

	When Berkeley Packet Filter Just in Time compiler is enabled, then compiled
	images are unknown addresses to the kernel, meaning they neither show up in
	traces nor in /proc/kallsyms. This enables export of these addresses, which
	can be used for debugging/tracing. If bpf_jit_harden is enabled, this feature
	is disabled.
	Values :
	0 - disable JIT kallsyms export (default value)
	1 - enable JIT kallsyms export for privileged users only

	dev_weight
	--------------

	The maximum number of packets that kernel can handle on a NAPI interrupt,
	it's a Per-CPU variable.
	Default: 64

	dev_weight_rx_bias
	--------------

	RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
	of the driver for the per softirq cycle netdev_budget. This parameter influences
	the proportion of the configured netdev_budget that is spent on RPS based packet
	processing during RX softirq cycles. It is further meant for making current
	dev_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 based
	on 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 asymmetric
	net 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 allows
	overriding the default of pfifo_fast with an alternative. Since the default
	queuing discipline is created without additional parameters so is best suited
	to queuing disciplines that work well without configuration like stochastic
	fair queue (sfq), CoDel (codel) or fair queue CoDel (fq_codel). Don't use
	queuing disciplines like Hierarchical Token Bucket or Deficit Round Robin
	which require setting up classes and bandwidths. Note that physical multiqueue
	interfaces still use mq as root qdisc, which in turn uses this default for its
	leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead
	default 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 feature
	globally 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 set
	sysctl.net.busy_read globally.
	Will increase power usage.
	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.

	tstamp_allow_data
	-----------------
	Allow processes to receive tx timestamps looped together with the original
	packet contents. If disabled, transmit timestamp requests from unprivileged
	processes 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.

	message_burst and message_cost
	------------------------------

	These parameters are used to limit the warning messages written to the kernel
	log from the networking code. They enforce a rate limit to make a
	denial-of-service attack impossible. A higher message_cost factor, results in
	fewer messages that will be written. Message_burst controls when messages will
	be dropped. The default settings limit warning messages to one every five
	seconds.

	warnings
	--------

	This sysctl is now unused.

	This was used to control console messages from the networking stack that
	occur because of problems on the network like duplicate address or bad
	checksums.

	These messages are now emitted at KERN_DEBUG and can generally be enabled
	and controlled by the dynamic_debug facility.

	netdev_budget
	-------------

	Maximum number of packets taken from all interfaces in one polling cycle (NAPI
	poll). In one polling cycle interfaces which are registered to polling are
	probed in a round-robin manner.

	netdev_max_backlog
	------------------

	Maximum number of packets, queued on the INPUT side, when the interface
	receives packets faster than kernel can process them.

	netdev_rss_key
	--------------

	RSS (Receive Side Scaling) enabled drivers use a 40 bytes host key that is
	randomly generated.
	Some user space might need to gather its content even if drivers do not
	provide 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: ... (52 bytes total)

	File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
	Note:
	/proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
	but most drivers only use 40 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, when
	the target CPU processes packets. It might give some delay on timestamps, but
	permit to distribute the load on several cpus.

	If set to 1 (default), timestamps are sampled as soon as possible, before
	queueing.

	optmem_max
	----------

	Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
	of struct cmsghdr structures with appended data.

	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 domain
	socket'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.txt and ipvs-sysctl.txt for
	descriptions of these entries.


	4. Appletalk
	-------------------------------------------------------

	The /proc/sys/net/appletalk directory holds the Appletalk configuration data
	when Appletalk is loaded. The configurable parameters are:

	aarp-expiry-time
	----------------

	The amount of time we keep an ARP entry before expiring it. Used to age out
	old hosts.

	aarp-resolve-time
	-----------------

	The amount of time we will spend trying to resolve an Appletalk address.

	aarp-retransmit-limit
	---------------------

	The number of times we will retransmit a query before giving up.

	aarp-tick-time
	--------------

	Controls the rate at which expires are checked.

	The directory /proc/net/appletalk holds the list of active Appletalk sockets
	on a machine.

	The fields indicate the DDP type, the local address (in network:node format)
	the remote address, the size of the transmit pending queue, the size of the
	received queue (bytes waiting for applications to read) the state and the uid
	owning the socket.

	/proc/net/atalk_iface lists all the interfaces configured for appletalk.It
	shows the name of the interface, its Appletalk address, the network range on
	that address (or network number for phase 1 networks), and the status of the
	interface.

	/proc/net/atalk_route lists each known network route. It lists the target
	(network) that the route leads to, the router (may be directly connected), the
	route flags, and the device the route is using.


	5. IPX
	-------------------------------------------------------

	The IPX protocol has no tunable values in proc/sys/net.

	The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
	socket giving the local and remote addresses in Novell format (that is
	network:node:port). In accordance with the strange Novell tradition,
	everything but the port is in hex. Not_Connected is displayed for sockets that
	are not tied to a specific remote address. The Tx and Rx queue sizes indicate
	the number of bytes pending for transmission and reception. The state
	indicates the state the socket is in and the uid is the owning uid of the
	socket.

	The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
	it gives the network number, the node number, and indicates if the network is
	the primary network. It also indicates which device it is bound to (or
	Internal for internal networks) and the Frame Type if appropriate. Linux
	supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
	IPX.

	The /proc/net/ipx_route table holds a list of IPX routes. For each route it
	gives the destination network, the router node (or Directly) and the network
	address of the router (or Connected) for internal networks.

	6. TIPC
	-------------------------------------------------------

	tipc_rmem
	----------

	The TIPC protocol now has a tunable for the receive memory, similar to the
	tcp_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 values
	are scaled (shifted) versions of that same value. Note that the min value
	is not at this point in time used in any meaningful way, but the triplet is
	preserved in order to be consistent with things like tcp_rmem.

	named_timeout
	--------------

	TIPC name table updates are distributed asynchronously in a cluster, without
	any form of transaction handling. This means that different race scenarios are
	possible. One such is that a name withdrawal sent out by one node and received
	by another node may arrive after a second, overlapping name publication already
	has been accepted from a third node, although the conflicting updates
	originally may have been issued in the correct sequential order.
	If named_timeout is nonzero, failed topology updates will be placed on a defer
	queue until another event arrives that clears the error, or until the timeout
	expires. Value is in milliseconds.