[NET] ip-sysctl.txt: Alphabetize. (ef56e622) · Commits · git / linux-net

Documentation/networking/ip-sysctl.txt

+177 −178

Original line number	Diff line number	Diff line
		@@ -101,6 +101,11 @@ inet_peer_gc_maxtime - INTEGER

		TCP variables:

		somaxconn - INTEGER
		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
		Defaults to 128. See also tcp_max_syn_backlog for additional tuning
		for TCP sockets.

		tcp_abc - INTEGER
		Controls Appropriate Byte Count (ABC) defined in RFC3465.
		ABC is a way of increasing congestion window (cwnd) more slowly
		@@ -112,48 +117,51 @@ tcp_abc - INTEGER
		of two segments to compensate for delayed acknowledgments.
		Default: 0 (off)

		tcp_syn_retries - INTEGER
		Number of times initial SYNs for an active TCP connection attempt
		will be retransmitted. Should not be higher than 255. Default value
		is 5, which corresponds to ~180seconds.
		tcp_abort_on_overflow - BOOLEAN
		If listening service is too slow to accept new connections,
		reset them. Default state is FALSE. It means that if overflow
		occurred due to a burst, connection will recover. Enable this
		option _only_ if you are really sure that listening daemon
		cannot be tuned to accept connections faster. Enabling this
		option can harm clients of your server.

		tcp_synack_retries - INTEGER
		Number of times SYNACKs for a passive TCP connection attempt will
		be retransmitted. Should not be higher than 255. Default value
		is 5, which corresponds to ~180seconds.
		tcp_adv_win_scale - INTEGER
		Count buffering overhead as bytes/2^tcp_adv_win_scale
		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
		if it is <= 0.
		Default: 2

		tcp_keepalive_time - INTEGER
		How often TCP sends out keepalive messages when keepalive is enabled.
		Default: 2hours.
		tcp_allowed_congestion_control - STRING
		Show/set the congestion control choices available to non-privileged
		processes. The list is a subset of those listed in
		tcp_available_congestion_control.
		Default is "reno" and the default setting (tcp_congestion_control).

		tcp_keepalive_probes - INTEGER
		How many keepalive probes TCP sends out, until it decides that the
		connection is broken. Default value: 9.
		tcp_app_win - INTEGER
		Reserve max(window/2^tcp_app_win, mss) of window for application
		buffer. Value 0 is special, it means that nothing is reserved.
		Default: 31

		tcp_keepalive_intvl - INTEGER
		How frequently the probes are send out. Multiplied by
		tcp_keepalive_probes it is time to kill not responding connection,
		after probes started. Default value: 75sec i.e. connection
		will be aborted after ~11 minutes of retries.
		tcp_available_congestion_control - STRING
		Shows the available congestion control choices that are registered.
		More congestion control algorithms may be available as modules,
		but not loaded.

		tcp_retries1 - INTEGER
		How many times to retry before deciding that something is wrong
		and it is necessary to report this suspicion to network layer.
		Minimal RFC value is 3, it is default, which corresponds
		to ~3sec-8min depending on RTO.
		tcp_congestion_control - STRING
		Set the congestion control algorithm to be used for new
		connections. The algorithm "reno" is always available, but
		additional choices may be available based on kernel configuration.
		Default is set as part of kernel configuration.

		tcp_retries2 - INTEGER
		How may times to retry before killing alive TCP connection.
		RFC1122 says that the limit should be longer than 100 sec.
		It is too small number. Default value 15 corresponds to ~13-30min
		depending on RTO.
		tcp_dsack - BOOLEAN
		Allows TCP to send "duplicate" SACKs.

		tcp_orphan_retries - INTEGER
		How may times to retry before killing TCP connection, closed
		by our side. Default value 7 corresponds to ~50sec-16min
		depending on RTO. If you machine is loaded WEB server,
		you should think about lowering this value, such sockets
		may consume significant resources. Cf. tcp_max_orphans.
		tcp_ecn - BOOLEAN
		Enable Explicit Congestion Notification in TCP.

		tcp_fack - BOOLEAN
		Enable FACK congestion avoidance and fast retransmission.
		The value is not used, if tcp_sack is not enabled.

		tcp_fin_timeout - INTEGER
		Time to hold socket in state FIN-WAIT-2, if it was closed
		@@ -166,24 +174,33 @@ tcp_fin_timeout - INTEGER
		because they eat maximum 1.5K of memory, but they tend
		to live longer. Cf. tcp_max_orphans.

		tcp_max_tw_buckets - INTEGER
		Maximal number of timewait sockets held by system simultaneously.
		If this number is exceeded time-wait socket is immediately destroyed
		and warning is printed. This limit exists only to prevent
		simple DoS attacks, you _must_ not lower the limit artificially,
		but rather increase it (probably, after increasing installed memory),
		if network conditions require more than default value.
		tcp_frto - BOOLEAN
		Enables F-RTO, an enhanced recovery algorithm for TCP retransmission
		timeouts. It is particularly beneficial in wireless environments
		where packet loss is typically due to random radio interference
		rather than intermediate router congestion.

		tcp_tw_recycle - BOOLEAN
		Enable fast recycling TIME-WAIT sockets. Default value is 0.
		It should not be changed without advice/request of technical
		experts.
		tcp_keepalive_time - INTEGER
		How often TCP sends out keepalive messages when keepalive is enabled.
		Default: 2hours.

		tcp_tw_reuse - BOOLEAN
		Allow to reuse TIME-WAIT sockets for new connections when it is
		safe from protocol viewpoint. Default value is 0.
		It should not be changed without advice/request of technical
		experts.
		tcp_keepalive_probes - INTEGER
		How many keepalive probes TCP sends out, until it decides that the
		connection is broken. Default value: 9.

		tcp_keepalive_intvl - INTEGER
		How frequently the probes are send out. Multiplied by
		tcp_keepalive_probes it is time to kill not responding connection,
		after probes started. Default value: 75sec i.e. connection
		will be aborted after ~11 minutes of retries.

		tcp_low_latency - BOOLEAN
		If set, the TCP stack makes decisions that prefer lower
		latency as opposed to higher throughput. By default, this
		option is not set meaning that higher throughput is preferred.
		An example of an application where this default should be
		changed would be a Beowulf compute cluster.
		Default: 0

		tcp_max_orphans - INTEGER
		Maximal number of TCP sockets not attached to any user file handle,
		@@ -197,41 +214,6 @@ tcp_max_orphans - INTEGER
		more aggressively. Let me to remind again: each orphan eats
		up to ~64K of unswappable memory.

		tcp_abort_on_overflow - BOOLEAN
		If listening service is too slow to accept new connections,
		reset them. Default state is FALSE. It means that if overflow
		occurred due to a burst, connection will recover. Enable this
		option _only_ if you are really sure that listening daemon
		cannot be tuned to accept connections faster. Enabling this
		option can harm clients of your server.

		tcp_syncookies - BOOLEAN
		Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
		Send out syncookies when the syn backlog queue of a socket
		overflows. This is to prevent against the common 'syn flood attack'
		Default: FALSE

		Note, that syncookies is fallback facility.
		It MUST NOT be used to help highly loaded servers to stand
		against legal connection rate. If you see synflood warnings
		in your logs, but investigation shows that they occur
		because of overload with legal connections, you should tune
		another parameters until this warning disappear.
		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.

		syncookies seriously violate TCP protocol, do not allow
		to use TCP extensions, can result in serious degradation
		of some services (f.e. SMTP relaying), visible not by you,
		but your clients and relays, contacting you. While you see
		synflood warnings in logs not being really flooded, your server
		is seriously misconfigured.

		tcp_stdurg - BOOLEAN
		Use the Host requirements interpretation of the TCP urg pointer field.
		Most hosts use the older BSD interpretation, so if you turn this on
		Linux might not communicate correctly with them.
		Default: FALSE

		tcp_max_syn_backlog - INTEGER
		Maximal number of remembered connection requests, which are
		still did not receive an acknowledgment from connecting client.
		@@ -239,24 +221,34 @@ tcp_max_syn_backlog - INTEGER
		and 128 for low memory machines. If server suffers of overload,
		try to increase this number.

		tcp_window_scaling - BOOLEAN
		Enable window scaling as defined in RFC1323.
		tcp_max_tw_buckets - INTEGER
		Maximal number of timewait sockets held by system simultaneously.
		If this number is exceeded time-wait socket is immediately destroyed
		and warning is printed. This limit exists only to prevent
		simple DoS attacks, you _must_ not lower the limit artificially,
		but rather increase it (probably, after increasing installed memory),
		if network conditions require more than default value.

		tcp_timestamps - BOOLEAN
		Enable timestamps as defined in RFC1323.
		tcp_mem - vector of 3 INTEGERs: min, pressure, max
		min: below this number of pages TCP is not bothered about its
		memory appetite.

		tcp_sack - BOOLEAN
		Enable select acknowledgments (SACKS).
		pressure: when amount of memory allocated by TCP exceeds this number
		of pages, TCP moderates its memory consumption and enters memory
		pressure mode, which is exited when memory consumption falls
		under "min".

		tcp_fack - BOOLEAN
		Enable FACK congestion avoidance and fast retransmission.
		The value is not used, if tcp_sack is not enabled.
		max: number of pages allowed for queueing by all TCP sockets.

		tcp_dsack - BOOLEAN
		Allows TCP to send "duplicate" SACKs.
		Defaults are calculated at boot time from amount of available
		memory.

		tcp_ecn - BOOLEAN
		Enable Explicit Congestion Notification in TCP.
		tcp_orphan_retries - INTEGER
		How may times to retry before killing TCP connection, closed
		by our side. Default value 7 corresponds to ~50sec-16min
		depending on RTO. If you machine is loaded WEB server,
		you should think about lowering this value, such sockets
		may consume significant resources. Cf. tcp_max_orphans.

		tcp_reordering - INTEGER
		Maximal reordering of packets in a TCP stream.
		@@ -267,20 +259,23 @@ tcp_retrans_collapse - BOOLEAN
		On retransmit try to send bigger packets to work around bugs in
		certain TCP stacks.

		tcp_wmem - vector of 3 INTEGERs: min, default, max
		min: Amount of memory reserved for send buffers for TCP socket.
		Each TCP socket has rights to use it due to fact of its birth.
		Default: 4K
		tcp_retries1 - INTEGER
		How many times to retry before deciding that something is wrong
		and it is necessary to report this suspicion to network layer.
		Minimal RFC value is 3, it is default, which corresponds
		to ~3sec-8min depending on RTO.

		default: Amount of memory allowed for send buffers for TCP socket
		by default. This value overrides net.core.wmem_default used
		by other protocols, it is usually lower than net.core.wmem_default.
		Default: 16K
		tcp_retries2 - INTEGER
		How may times to retry before killing alive TCP connection.
		RFC1122 says that the limit should be longer than 100 sec.
		It is too small number. Default value 15 corresponds to ~13-30min
		depending on RTO.

		max: Maximal amount of memory allowed for automatically selected
		send buffers for TCP socket. This value does not override
		net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
		Default: 128K
		tcp_rfc1337 - BOOLEAN
		If set, the TCP stack behaves conforming to RFC1337. If unset,
		we are not conforming to RFC, but prevent TCP TIME_WAIT
		assassination.
		Default: 0

		tcp_rmem - vector of 3 INTEGERs: min, default, max
		min: Minimal size of receive buffer used by TCP sockets.
		@@ -299,44 +294,55 @@ tcp_rmem - vector of 3 INTEGERs: min, default, max
		net.core.rmem_max, "static" selection via SO_RCVBUF does not use this.
		Default: 87380*2 bytes.

		tcp_mem - vector of 3 INTEGERs: min, pressure, max
		min: below this number of pages TCP is not bothered about its
		memory appetite.
		tcp_sack - BOOLEAN
		Enable select acknowledgments (SACKS).

		pressure: when amount of memory allocated by TCP exceeds this number
		of pages, TCP moderates its memory consumption and enters memory
		pressure mode, which is exited when memory consumption falls
		under "min".
		tcp_slow_start_after_idle - BOOLEAN
		If set, provide RFC2861 behavior and time out the congestion
		window after an idle period. An idle period is defined at
		the current RTO. If unset, the congestion window will not
		be timed out after an idle period.
		Default: 1

		max: number of pages allowed for queueing by all TCP sockets.
		tcp_stdurg - BOOLEAN
		Use the Host requirements interpretation of the TCP urg pointer field.
		Most hosts use the older BSD interpretation, so if you turn this on
		Linux might not communicate correctly with them.
		Default: FALSE

		Defaults are calculated at boot time from amount of available
		memory.
		tcp_synack_retries - INTEGER
		Number of times SYNACKs for a passive TCP connection attempt will
		be retransmitted. Should not be higher than 255. Default value
		is 5, which corresponds to ~180seconds.

		tcp_app_win - INTEGER
		Reserve max(window/2^tcp_app_win, mss) of window for application
		buffer. Value 0 is special, it means that nothing is reserved.
		Default: 31
		tcp_syncookies - BOOLEAN
		Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
		Send out syncookies when the syn backlog queue of a socket
		overflows. This is to prevent against the common 'syn flood attack'
		Default: FALSE

		tcp_adv_win_scale - INTEGER
		Count buffering overhead as bytes/2^tcp_adv_win_scale
		(if tcp_adv_win_scale > 0) or bytes-bytes/2^(-tcp_adv_win_scale),
		if it is <= 0.
		Default: 2
		Note, that syncookies is fallback facility.
		It MUST NOT be used to help highly loaded servers to stand
		against legal connection rate. If you see synflood warnings
		in your logs, but investigation shows that they occur
		because of overload with legal connections, you should tune
		another parameters until this warning disappear.
		See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow.

		tcp_rfc1337 - BOOLEAN
		If set, the TCP stack behaves conforming to RFC1337. If unset,
		we are not conforming to RFC, but prevent TCP TIME_WAIT
		assassination.
		Default: 0
		syncookies seriously violate TCP protocol, do not allow
		to use TCP extensions, can result in serious degradation
		of some services (f.e. SMTP relaying), visible not by you,
		but your clients and relays, contacting you. While you see
		synflood warnings in logs not being really flooded, your server
		is seriously misconfigured.

		tcp_low_latency - BOOLEAN
		If set, the TCP stack makes decisions that prefer lower
		latency as opposed to higher throughput. By default, this
		option is not set meaning that higher throughput is preferred.
		An example of an application where this default should be
		changed would be a Beowulf compute cluster.
		Default: 0
		tcp_syn_retries - INTEGER
		Number of times initial SYNs for an active TCP connection attempt
		will be retransmitted. Should not be higher than 255. Default value
		is 5, which corresponds to ~180seconds.

		tcp_timestamps - BOOLEAN
		Enable timestamps as defined in RFC1323.

		tcp_tso_win_divisor - INTEGER
		This allows control over what percentage of the congestion window
		@@ -345,33 +351,34 @@ tcp_tso_win_divisor - INTEGER
		building larger TSO frames.
		Default: 3

		tcp_frto - BOOLEAN
		Enables F-RTO, an enhanced recovery algorithm for TCP retransmission
		timeouts. It is particularly beneficial in wireless environments
		where packet loss is typically due to random radio interference
		rather than intermediate router congestion.
		tcp_tw_recycle - BOOLEAN
		Enable fast recycling TIME-WAIT sockets. Default value is 0.
		It should not be changed without advice/request of technical
		experts.

		tcp_allowed_congestion_control - STRING
		Show/set the congestion control choices available to non-privileged
		processes. The list is a subset of those listed in
		tcp_available_congestion_control.
		Default is "reno" and the default setting (tcp_congestion_control).
		tcp_tw_reuse - BOOLEAN
		Allow to reuse TIME-WAIT sockets for new connections when it is
		safe from protocol viewpoint. Default value is 0.
		It should not be changed without advice/request of technical
		experts.

		tcp_available_congestion_control - STRING
		Shows the available congestion control choices that are registered.
		More congestion control algorithms may be available as modules,
		but not loaded.
		tcp_window_scaling - BOOLEAN
		Enable window scaling as defined in RFC1323.

		tcp_congestion_control - STRING
		Set the congestion control algorithm to be used for new
		connections. The algorithm "reno" is always available, but
		additional choices may be available based on kernel configuration.
		Default is set as part of kernel configuration.
		tcp_wmem - vector of 3 INTEGERs: min, default, max
		min: Amount of memory reserved for send buffers for TCP socket.
		Each TCP socket has rights to use it due to fact of its birth.
		Default: 4K

		somaxconn - INTEGER
		Limit of socket listen() backlog, known in userspace as SOMAXCONN.
		Defaults to 128. See also tcp_max_syn_backlog for additional tuning
		for TCP sockets.
		default: Amount of memory allowed for send buffers for TCP socket
		by default. This value overrides net.core.wmem_default used
		by other protocols, it is usually lower than net.core.wmem_default.
		Default: 16K

		max: Maximal amount of memory allowed for automatically selected
		send buffers for TCP socket. This value does not override
		net.core.wmem_max, "static" selection via SO_SNDBUF does not use this.
		Default: 128K

		tcp_workaround_signed_windows - BOOLEAN
		If set, assume no receipt of a window scaling option means the
		@@ -380,13 +387,6 @@ tcp_workaround_signed_windows - BOOLEAN
		not receive a window scaling option from them.
		Default: 0

		tcp_slow_start_after_idle - BOOLEAN
		If set, provide RFC2861 behavior and time out the congestion
		window after an idle period. An idle period is defined at
		the current RTO. If unset, the congestion window will not
		be timed out after an idle period.
		Default: 1

		CIPSOv4 Variables:

		cipso_cache_enable - BOOLEAN
		@@ -986,4 +986,3 @@ no_cong_thresh FIXME
		slot_timeout FIXME
		warn_noreply_time FIXME

		$Id: ip-sysctl.txt,v 1.20 2001/12/13 09:00:18 davem Exp $