.. _user_agent:

.. raw:: html

	<a name="user_agent"></a>

+------------+--------+----------------------------------+
| name       | type   | default                          |
+============+========+==================================+
| user_agent | string | "libtorrent/" LIBTORRENT_VERSION |
+------------+--------+----------------------------------+

this is the client identification to the tracker. The recommended
format of this string is: "ClientName/ClientVersion
libtorrent/libtorrentVersion". This name will not only be used when
making HTTP requests, but also when sending extended headers to
peers that support that extension. It may not contain \r or \n

.. _announce_ip:

.. raw:: html

	<a name="announce_ip"></a>

+-------------+--------+---------+
| name        | type   | default |
+=============+========+=========+
| announce_ip | string | 0       |
+-------------+--------+---------+

``announce_ip`` is the ip address passed along to trackers as the
``&ip=`` parameter. If left as the default, that parameter is
omitted.

.. _mmap_cache:

.. raw:: html

	<a name="mmap_cache"></a>

+------------+--------+---------+
| name       | type   | default |
+============+========+=========+
| mmap_cache | string | 0       |
+------------+--------+---------+

``mmap_cache`` may be set to a filename where the disk cache will
be mmapped to. This could be useful, for instance, to map the disk
cache from regular rotating hard drives onto an SSD drive. Doing
that effectively introduces a second layer of caching, allowing the
disk cache to be as big as can fit on an SSD drive (probably about
one order of magnitude more than the available RAM). The intention
of this setting is to set it up once at the start up and not change
it while running. The setting may not be changed as long as there
are any disk buffers in use. This default to the empty string,
which means use regular RAM allocations for the disk cache. The
file specified will be created and truncated to the disk cache size
(``cache_size``). Any existing file with the same name will be
replaced.

Since this setting sets a hard upper limit on cache usage, it
cannot be combined with
``session_settings::contiguous_recv_buffer``, since that feature
treats the ``cache_size`` setting as a soft (but still pretty hard)
limit. The result of combining the two is peers being disconnected
after failing to allocate more disk buffers.

This feature requires the ``mmap`` system call, on systems that
don't have ``mmap`` this setting is ignored.

.. _handshake_client_version:

.. raw:: html

	<a name="handshake_client_version"></a>

+--------------------------+--------+---------+
| name                     | type   | default |
+==========================+========+=========+
| handshake_client_version | string | 0       |
+--------------------------+--------+---------+

this is the client name and version identifier sent to peers in the
handshake message. If this is an empty string, the user_agent is
used instead

.. _outgoing_interfaces:

.. raw:: html

	<a name="outgoing_interfaces"></a>

+---------------------+--------+---------+
| name                | type   | default |
+=====================+========+=========+
| outgoing_interfaces | string | ""      |
+---------------------+--------+---------+

sets the network interface this session will use when it opens
outgoing connections. By default, it binds outgoing connections to
INADDR_ANY and port 0 (i.e. let the OS decide). Ths parameter must
be a string containing one or more, comma separated, adapter names.
Adapter names on unix systems are of the form "eth0", "eth1",
"tun0", etc. When specifying multiple interfaces, they will be
assigned in round-robin order. This may be useful for clients that
are multi-homed. Binding an outgoing connection to a local IP does
not necessarily make the connection via the associated NIC/Adapter.
Setting this to an empty string will disable binding of outgoing
connections.

.. _listen_interfaces:

.. raw:: html

	<a name="listen_interfaces"></a>

+-------------------+--------+----------------+
| name              | type   | default        |
+===================+========+================+
| listen_interfaces | string | "0.0.0.0:6881" |
+-------------------+--------+----------------+

a comma-separated list of (IP or device name, port) pairs. These
are the listen ports that will be opened for accepting incoming uTP
and TCP connections. It is possible to listen on multiple
interfaces and multiple ports. Binding to port 0 will make the
operating system pick the port. The default is "0.0.0.0:0", which
binds to all interfaces on a port the OS picks.
if binding fails, the listen_failed_alert is posted, otherwise the
listen_succeeded_alert.
If the DHT is running, it will also have its socket rebound to the
same port as the main listen port.

The reason why it's a good idea to run the DHT and the bittorrent
socket on the same port is because that is an assumption that may
be used to increase performance. One way to accelerate the
connecting of peers on windows may be to first ping all peers with
a DHT ping packet, and connect to those that responds first. On
windows one can only connect to a few peers at a time because of a
built in limitation (in XP Service pack 2).

.. _proxy_hostname:

.. raw:: html

	<a name="proxy_hostname"></a>

+----------------+--------+---------+
| name           | type   | default |
+================+========+=========+
| proxy_hostname | string | ""      |
+----------------+--------+---------+

when using a poxy, this is the hostname where the proxy is running
see proxy_type.

.. _proxy_username:

.. _proxy_password:

.. raw:: html

	<a name="proxy_username"></a>
	<a name="proxy_password"></a>

+----------------+--------+---------+
| name           | type   | default |
+================+========+=========+
| proxy_username | string | ""      |
+----------------+--------+---------+
| proxy_password | string | ""      |
+----------------+--------+---------+

when using a proxy, these are the credentials (if any) to use whne
connecting to it. see proxy_type

.. _i2p_hostname:

.. raw:: html

	<a name="i2p_hostname"></a>

+--------------+--------+---------+
| name         | type   | default |
+==============+========+=========+
| i2p_hostname | string | ""      |
+--------------+--------+---------+

sets the i2p_ SAM bridge to connect to. set the port with the
``i2p_port`` setting.

.. _i2p: http://www.i2p2.de

.. _peer_fingerprint:

.. raw:: html

	<a name="peer_fingerprint"></a>

+------------------+--------+------------+
| name             | type   | default    |
+==================+========+============+
| peer_fingerprint | string | "-LT1100-" |
+------------------+--------+------------+

this is the fingerprint for the client. It will be used as the
prefix to the peer_id. If this is 20 bytes (or longer) it will be
used as the peer-id

.. _allow_multiple_connections_per_ip:

.. raw:: html

	<a name="allow_multiple_connections_per_ip"></a>

+-----------------------------------+------+---------+
| name                              | type | default |
+===================================+======+=========+
| allow_multiple_connections_per_ip | bool | false   |
+-----------------------------------+------+---------+

determines if connections from the same IP address as existing
connections should be rejected or not. Multiple connections from
the same IP address is not allowed by default, to prevent abusive
behavior by peers. It may be useful to allow such connections in
cases where simulations are run on the same machie, and all peers
in a swarm has the same IP address.

.. _send_redundant_have:

.. raw:: html

	<a name="send_redundant_have"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| send_redundant_have | bool | true    |
+---------------------+------+---------+

if set to true, upload, download and unchoke limits are ignored for
peers on the local network. This option is *DEPRECATED*, please use
set_peer_class_filter() instead.
``send_redundant_have`` controls if have messages will be sent to
peers that already have the piece. This is typically not necessary,
but it might be necessary for collecting statistics in some cases.
Default is false.

.. _lazy_bitfields:

.. raw:: html

	<a name="lazy_bitfields"></a>

+----------------+------+---------+
| name           | type | default |
+================+======+=========+
| lazy_bitfields | bool | false   |
+----------------+------+---------+

if this is true, outgoing bitfields will never be fuil. If the
client is seed, a few bits will be set to 0, and later filled in
with have messages. This is to prevent certain ISPs from stopping
people from seeding.

.. _use_dht_as_fallback:

.. raw:: html

	<a name="use_dht_as_fallback"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| use_dht_as_fallback | bool | false   |
+---------------------+------+---------+

``use_dht_as_fallback`` determines how the DHT is used. If this is
true, the DHT will only be used for torrents where all trackers in
its tracker list has failed. Either by an explicit error message or
a time out. This is false by default, which means the DHT is used
by default regardless of if the trackers fail or not.

.. _upnp_ignore_nonrouters:

.. raw:: html

	<a name="upnp_ignore_nonrouters"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| upnp_ignore_nonrouters | bool | false   |
+------------------------+------+---------+

``upnp_ignore_nonrouters`` indicates whether or not the UPnP
implementation should ignore any broadcast response from a device
whose address is not the configured router for this machine. i.e.
it's a way to not talk to other people's routers by mistake.

.. _use_parole_mode:

.. raw:: html

	<a name="use_parole_mode"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| use_parole_mode | bool | true    |
+-----------------+------+---------+

``use_parole_mode`` specifies if parole mode should be used. Parole
mode means that peers that participate in pieces that fail the hash
check are put in a mode where they are only allowed to download
whole pieces. If the whole piece a peer in parole mode fails the
hash check, it is banned. If a peer participates in a piece that
passes the hash check, it is taken out of parole mode.

.. _use_read_cache:

.. _use_write_cache:

.. raw:: html

	<a name="use_read_cache"></a>
	<a name="use_write_cache"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| use_read_cache  | bool | true    |
+-----------------+------+---------+
| use_write_cache | bool | true    |
+-----------------+------+---------+

enable and disable caching of read blocks and blocks to be written
to disk respsectively. the purpose of the read cache is partly
read-ahead of requests but also to avoid reading blocks back from
the disk multiple times for popular pieces. the write cache purpose
is to hold off writing blocks to disk until they have been hashed,
to avoid having to read them back in again.

.. _dont_flush_write_cache:

.. raw:: html

	<a name="dont_flush_write_cache"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| dont_flush_write_cache | bool | false   |
+------------------------+------+---------+

this will make the disk cache never flush a write piece if it would
cause is to have to re-read it once we want to calculate the piece
hash

.. _explicit_read_cache:

.. raw:: html

	<a name="explicit_read_cache"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| explicit_read_cache | bool | false   |
+---------------------+------+---------+

``explicit_read_cache`` defaults to 0. If set to something greater
than 0, the disk read cache will not be evicted by cache misses and
will explicitly be controlled based on the rarity of pieces. Rare
pieces are more likely to be cached. This would typically be used
together with ``suggest_mode`` set to ``suggest_read_cache``. The
value is the number of pieces to keep in the read cache. If the
actual read cache can't fit as many, it will essentially be
clamped.

.. _coalesce_reads:

.. _coalesce_writes:

.. raw:: html

	<a name="coalesce_reads"></a>
	<a name="coalesce_writes"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| coalesce_reads  | bool | false   |
+-----------------+------+---------+
| coalesce_writes | bool | false   |
+-----------------+------+---------+

allocate separate, contiguous, buffers for read and write calls.
Only used where writev/readv cannot be used will use more RAM but
may improve performance

.. _auto_manage_prefer_seeds:

.. raw:: html

	<a name="auto_manage_prefer_seeds"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| auto_manage_prefer_seeds | bool | false   |
+--------------------------+------+---------+

prefer seeding torrents when determining which torrents to give
active slots to, the default is false which gives preference to
downloading torrents

.. _dont_count_slow_torrents:

.. raw:: html

	<a name="dont_count_slow_torrents"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| dont_count_slow_torrents | bool | true    |
+--------------------------+------+---------+

if ``dont_count_slow_torrents`` is true, torrents without any
payload transfers are not subject to the ``active_seeds`` and
``active_downloads`` limits. This is intended to make it more
likely to utilize all available bandwidth, and avoid having
torrents that don't transfer anything block the active slots.

.. _close_redundant_connections:

.. raw:: html

	<a name="close_redundant_connections"></a>

+-----------------------------+------+---------+
| name                        | type | default |
+=============================+======+=========+
| close_redundant_connections | bool | true    |
+-----------------------------+------+---------+

``close_redundant_connections`` specifies whether libtorrent should
close connections where both ends have no utility in keeping the
connection open. For instance if both ends have completed their
downloads, there's no point in keeping it open.

.. _prioritize_partial_pieces:

.. raw:: html

	<a name="prioritize_partial_pieces"></a>

+---------------------------+------+---------+
| name                      | type | default |
+===========================+======+=========+
| prioritize_partial_pieces | bool | false   |
+---------------------------+------+---------+

If ``prioritize_partial_pieces`` is true, partial pieces are picked
before pieces that are more rare. If false, rare pieces are always
prioritized, unless the number of partial pieces is growing out of
proportion.

.. _rate_limit_ip_overhead:

.. raw:: html

	<a name="rate_limit_ip_overhead"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| rate_limit_ip_overhead | bool | true    |
+------------------------+------+---------+

if set to true, the estimated TCP/IP overhead is drained from the
rate limiters, to avoid exceeding the limits with the total traffic

.. _announce_to_all_tiers:

.. _announce_to_all_trackers:

.. raw:: html

	<a name="announce_to_all_tiers"></a>
	<a name="announce_to_all_trackers"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| announce_to_all_tiers    | bool | false   |
+--------------------------+------+---------+
| announce_to_all_trackers | bool | false   |
+--------------------------+------+---------+

``announce_to_all_trackers`` controls how multi tracker torrents
are treated. If this is set to true, all trackers in the same tier
are announced to in parallel. If all trackers in tier 0 fails, all
trackers in tier 1 are announced as well. If it's set to false, the
behavior is as defined by the multi tracker specification. It
defaults to false, which is the same behavior previous versions of
libtorrent has had as well.

``announce_to_all_tiers`` also controls how multi tracker torrents
are treated. When this is set to true, one tracker from each tier
is announced to. This is the uTorrent behavior. This is false by
default in order to comply with the multi-tracker specification.

.. _prefer_udp_trackers:

.. raw:: html

	<a name="prefer_udp_trackers"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| prefer_udp_trackers | bool | true    |
+---------------------+------+---------+

``prefer_udp_trackers`` is true by default. It means that trackers
may be rearranged in a way that udp trackers are always tried
before http trackers for the same hostname. Setting this to false
means that the trackers' tier is respected and there's no
preference of one protocol over another.

.. _strict_super_seeding:

.. raw:: html

	<a name="strict_super_seeding"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| strict_super_seeding | bool | false   |
+----------------------+------+---------+

``strict_super_seeding`` when this is set to true, a piece has to
have been forwarded to a third peer before another one is handed
out. This is the traditional definition of super seeding.

.. _lock_disk_cache:

.. raw:: html

	<a name="lock_disk_cache"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| lock_disk_cache | bool | false   |
+-----------------+------+---------+

if this is set to true, the memory allocated for the disk cache
will be locked in physical RAM, never to be swapped out. Every time
a disk buffer is allocated and freed, there will be the extra
overhead of a system call.

.. _disable_hash_checks:

.. raw:: html

	<a name="disable_hash_checks"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| disable_hash_checks | bool | false   |
+---------------------+------+---------+

when set to true, all data downloaded from peers will be assumed to
be correct, and not tested to match the hashes in the torrent this
is only useful for simulation and testing purposes (typically
combined with disabled_storage)

.. _allow_i2p_mixed:

.. raw:: html

	<a name="allow_i2p_mixed"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| allow_i2p_mixed | bool | false   |
+-----------------+------+---------+

if this is true, i2p torrents are allowed to also get peers from
other sources than the tracker, and connect to regular IPs, not
providing any anonymization. This may be useful if the user is not
interested in the anonymization of i2p, but still wants to be able
to connect to i2p peers.

.. _low_prio_disk:

.. raw:: html

	<a name="low_prio_disk"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| low_prio_disk | bool | true    |
+---------------+------+---------+

``low_prio_disk`` determines if the disk I/O should use a normal or
low priority policy. This defaults to true, which means that it's
low priority by default. Other processes doing disk I/O will
normally take priority in this mode. This is meant to improve the
overall responsiveness of the system while downloading in the
background. For high-performance server setups, this might not be
desirable.

.. _volatile_read_cache:

.. raw:: html

	<a name="volatile_read_cache"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| volatile_read_cache | bool | false   |
+---------------------+------+---------+

``volatile_read_cache``, if this is set to true, read cache blocks
that are hit by peer read requests are removed from the disk cache
to free up more space. This is useful if you don't expect the disk
cache to create any cache hits from other peers than the one who
triggered the cache line to be read into the cache in the first
place.

.. _guided_read_cache:

.. raw:: html

	<a name="guided_read_cache"></a>

+-------------------+------+---------+
| name              | type | default |
+===================+======+=========+
| guided_read_cache | bool | false   |
+-------------------+------+---------+

``guided_read_cache`` enables the disk cache to adjust the size of
a cache line generated by peers to depend on the upload rate you
are sending to that peer. The intention is to optimize the RAM
usage of the cache, to read ahead further for peers that you're
sending faster to.

.. _no_atime_storage:

.. raw:: html

	<a name="no_atime_storage"></a>

+------------------+------+---------+
| name             | type | default |
+==================+======+=========+
| no_atime_storage | bool | true    |
+------------------+------+---------+

``no_atime_storage`` this is a linux-only option and passes in the
``O_NOATIME`` to ``open()`` when opening files. This may lead to
some disk performance improvements.

.. _incoming_starts_queued_torrents:

.. raw:: html

	<a name="incoming_starts_queued_torrents"></a>

+---------------------------------+------+---------+
| name                            | type | default |
+=================================+======+=========+
| incoming_starts_queued_torrents | bool | false   |
+---------------------------------+------+---------+

``incoming_starts_queued_torrents`` defaults to false. If a torrent
has been paused by the auto managed feature in libtorrent, i.e. the
torrent is paused and auto managed, this feature affects whether or
not it is automatically started on an incoming connection. The main
reason to queue torrents, is not to make them unavailable, but to
save on the overhead of announcing to the trackers, the DHT and to
avoid spreading one's unchoke slots too thin. If a peer managed to
find us, even though we're no in the torrent anymore, this setting
can make us start the torrent and serve it.

.. _report_true_downloaded:

.. raw:: html

	<a name="report_true_downloaded"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| report_true_downloaded | bool | false   |
+------------------------+------+---------+

when set to true, the downloaded counter sent to trackers will
include the actual number of payload bytes donwnloaded including
redundant bytes. If set to false, it will not include any redundany
bytes

.. _strict_end_game_mode:

.. raw:: html

	<a name="strict_end_game_mode"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| strict_end_game_mode | bool | true    |
+----------------------+------+---------+

``strict_end_game_mode`` defaults to true, and controls when a
block may be requested twice. If this is ``true``, a block may only
be requested twice when there's ay least one request to every piece
that's left to download in the torrent. This may slow down progress
on some pieces sometimes, but it may also avoid downloading a lot
of redundant bytes. If this is ``false``, libtorrent attempts to
use each peer connection to its max, by always requesting
something, even if it means requesting something that has been
requested from another peer already.

.. _broadcast_lsd:

.. raw:: html

	<a name="broadcast_lsd"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| broadcast_lsd | bool | true    |
+---------------+------+---------+

if ``broadcast_lsd`` is set to true, the local peer discovery (or
Local Service Discovery) will not only use IP multicast, but also
broadcast its messages. This can be useful when running on networks
that don't support multicast. Since broadcast messages might be
expensive and disruptive on networks, only every 8th announce uses
broadcast.

.. _enable_outgoing_utp:

.. _enable_incoming_utp:

.. _enable_outgoing_tcp:

.. _enable_incoming_tcp:

.. raw:: html

	<a name="enable_outgoing_utp"></a>
	<a name="enable_incoming_utp"></a>
	<a name="enable_outgoing_tcp"></a>
	<a name="enable_incoming_tcp"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| enable_outgoing_utp | bool | true    |
+---------------------+------+---------+
| enable_incoming_utp | bool | true    |
+---------------------+------+---------+
| enable_outgoing_tcp | bool | true    |
+---------------------+------+---------+
| enable_incoming_tcp | bool | true    |
+---------------------+------+---------+

when set to true, libtorrent will try to make outgoing utp
connections controls whether libtorrent will accept incoming
connections or make outgoing connections of specific type.

.. _ignore_resume_timestamps:

.. raw:: html

	<a name="ignore_resume_timestamps"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| ignore_resume_timestamps | bool | false   |
+--------------------------+------+---------+

``ignore_resume_timestamps`` determines if the storage, when
loading resume data files, should verify that the file modification
time with the timestamps in the resume data. This defaults to
false, which means timestamps are taken into account, and resume
data is less likely to accepted (torrents are more likely to be
fully checked when loaded). It might be useful to set this to true
if your network is faster than your disk, and it would be faster to
redownload potentially missed pieces than to go through the whole
storage to look for them.

.. _no_recheck_incomplete_resume:

.. raw:: html

	<a name="no_recheck_incomplete_resume"></a>

+------------------------------+------+---------+
| name                         | type | default |
+==============================+======+=========+
| no_recheck_incomplete_resume | bool | false   |
+------------------------------+------+---------+

``no_recheck_incomplete_resume`` determines if the storage should
check the whole files when resume data is incomplete or missing or
whether it should simply assume we don't have any of the data. By
default, this is determined by the existance of any of the files.
By setting this setting to true, the files won't be checked, but
will go straight to download mode.

.. _anonymous_mode:

.. raw:: html

	<a name="anonymous_mode"></a>

+----------------+------+---------+
| name           | type | default |
+================+======+=========+
| anonymous_mode | bool | false   |
+----------------+------+---------+

``anonymous_mode`` defaults to false. When set to true, the client
tries to hide its identity to a certain degree. The peer-ID will no
longer include the client's fingerprint. The user-agent will be
reset to an empty string. Trackers will only be used if they are
using a proxy server. The listen sockets are closed, and incoming
connections will only be accepted through a SOCKS5 or I2P proxy (if
a peer proxy is set up and is run on the same machine as the
tracker proxy). Since no incoming connections are accepted,
NAT-PMP, UPnP, DHT and local peer discovery are all turned off when
this setting is enabled.

If you're using I2P, it might make sense to enable anonymous mode
as well.

.. _report_web_seed_downloads:

.. raw:: html

	<a name="report_web_seed_downloads"></a>

+---------------------------+------+---------+
| name                      | type | default |
+===========================+======+=========+
| report_web_seed_downloads | bool | true    |
+---------------------------+------+---------+

specifies whether downloads from web seeds is reported to the
tracker or not. Defaults to on. Turning it off also excludes web
seed traffic from other stats and download rate reporting via the
libtorrent API.

.. _utp_dynamic_sock_buf:

.. raw:: html

	<a name="utp_dynamic_sock_buf"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| utp_dynamic_sock_buf | bool | true    |
+----------------------+------+---------+

controls if the uTP socket manager is allowed to increase the
socket buffer if a network interface with a large MTU is used (such
as loopback or ethernet jumbo frames). This defaults to true and
might improve uTP throughput. For RAM constrained systems,
disabling this typically saves around 30kB in user space and
probably around 400kB in kernel socket buffers (it adjusts the send
and receive buffer size on the kernel socket, both for IPv4 and
IPv6).

.. _announce_double_nat:

.. raw:: html

	<a name="announce_double_nat"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| announce_double_nat | bool | false   |
+---------------------+------+---------+

set to true if uTP connections should be rate limited This option
is *DEPRECATED*, please use set_peer_class_filter() instead.
if this is true, the ``&ip=`` argument in tracker requests (unless
otherwise specified) will be set to the intermediate IP address if
the user is double NATed. If ther user is not double NATed, this
option does not have an affect

.. _seeding_outgoing_connections:

.. raw:: html

	<a name="seeding_outgoing_connections"></a>

+------------------------------+------+---------+
| name                         | type | default |
+==============================+======+=========+
| seeding_outgoing_connections | bool | true    |
+------------------------------+------+---------+

``seeding_outgoing_connections`` determines if seeding (and
finished) torrents should attempt to make outgoing connections or
not. By default this is true. It may be set to false in very
specific applications where the cost of making outgoing connections
is high, and there are no or small benefits of doing so. For
instance, if no nodes are behind a firewall or a NAT, seeds don't
need to make outgoing connections.

.. _no_connect_privileged_ports:

.. raw:: html

	<a name="no_connect_privileged_ports"></a>

+-----------------------------+------+---------+
| name                        | type | default |
+=============================+======+=========+
| no_connect_privileged_ports | bool | false   |
+-----------------------------+------+---------+

when this is true, libtorrent will not attempt to make outgoing
connections to peers whose port is < 1024. This is a safety
precaution to avoid being part of a DDoS attack

.. _smooth_connects:

.. raw:: html

	<a name="smooth_connects"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| smooth_connects | bool | true    |
+-----------------+------+---------+

``smooth_connects`` is true by default, which means the number of
connection attempts per second may be limited to below the
``connection_speed``, in case we're close to bump up against the
limit of number of connections. The intention of this setting is to
more evenly distribute our connection attempts over time, instead
of attempting to connectin in batches, and timing them out in
batches.

.. _always_send_user_agent:

.. raw:: html

	<a name="always_send_user_agent"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| always_send_user_agent | bool | false   |
+------------------------+------+---------+

always send user-agent in every web seed request. If false, only
the first request per http connection will include the user agent

.. _apply_ip_filter_to_trackers:

.. raw:: html

	<a name="apply_ip_filter_to_trackers"></a>

+-----------------------------+------+---------+
| name                        | type | default |
+=============================+======+=========+
| apply_ip_filter_to_trackers | bool | true    |
+-----------------------------+------+---------+

``apply_ip_filter_to_trackers`` defaults to true. It determines
whether the IP filter applies to trackers as well as peers. If this
is set to false, trackers are exempt from the IP filter (if there
is one). If no IP filter is set, this setting is irrelevant.

.. _use_disk_read_ahead:

.. raw:: html

	<a name="use_disk_read_ahead"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| use_disk_read_ahead | bool | true    |
+---------------------+------+---------+

``use_disk_read_ahead`` defaults to true and will attempt to
optimize disk reads by giving the operating system heads up of disk
read requests as they are queued in the disk job queue.

.. _lock_files:

.. raw:: html

	<a name="lock_files"></a>

+------------+------+---------+
| name       | type | default |
+============+======+=========+
| lock_files | bool | false   |
+------------+------+---------+

``lock_files`` determines whether or not to lock files which
libtorrent is downloading to or seeding from. This is implemented
using ``fcntl(F_SETLK)`` on unix systems and by not passing in
``SHARE_READ`` and ``SHARE_WRITE`` on windows. This might prevent
3rd party processes from corrupting the files under libtorrent's
feet.

.. _contiguous_recv_buffer:

.. raw:: html

	<a name="contiguous_recv_buffer"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| contiguous_recv_buffer | bool | true    |
+------------------------+------+---------+

``contiguous_recv_buffer`` determines whether or not libtorrent
should receive data from peers into a contiguous intermediate
buffer, to then copy blocks into disk buffers from, or to make many
smaller calls to ``read()``, each time passing in the specific
buffer the data belongs in. When downloading at high rates, the
latter may save some time copying data. When seeding at high rates,
all incoming traffic consists of a very large number of tiny
packets, and enabling ``contiguous_recv_buffer`` will provide
higher performance. When this is enabled, it will only be used when
seeding to peers, since that's when it provides performance
improvements.

.. _ban_web_seeds:

.. raw:: html

	<a name="ban_web_seeds"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| ban_web_seeds | bool | true    |
+---------------+------+---------+

when true, web seeds sending bad data will be banned

.. _allow_partial_disk_writes:

.. raw:: html

	<a name="allow_partial_disk_writes"></a>

+---------------------------+------+---------+
| name                      | type | default |
+===========================+======+=========+
| allow_partial_disk_writes | bool | true    |
+---------------------------+------+---------+

when set to false, the ``write_cache_line_size`` will apply across
piece boundaries. this is a bad idea unless the piece picker also
is configured to have an affinity to pick pieces belonging to the
same write cache line as is configured in the disk cache.

.. _force_proxy:

.. raw:: html

	<a name="force_proxy"></a>

+-------------+------+---------+
| name        | type | default |
+=============+======+=========+
| force_proxy | bool | false   |
+-------------+------+---------+

If true, disables any communication that's not going over a proxy.
Enabling this requires a proxy to be configured as well, see
``set_proxy_settings``. The listen sockets are closed, and incoming
connections will only be accepted through a SOCKS5 or I2P proxy (if
a peer proxy is set up and is run on the same machine as the
tracker proxy). This setting also disabled peer country lookups,
since those are done via DNS lookups that aren't supported by
proxies.

.. _support_share_mode:

.. raw:: html

	<a name="support_share_mode"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| support_share_mode | bool | true    |
+--------------------+------+---------+

if false, prevents libtorrent to advertise share-mode support

.. _support_merkle_torrents:

.. raw:: html

	<a name="support_merkle_torrents"></a>

+-------------------------+------+---------+
| name                    | type | default |
+=========================+======+=========+
| support_merkle_torrents | bool | true    |
+-------------------------+------+---------+

if this is false, don't advertise support for the Tribler merkle
tree piece message

.. _report_redundant_bytes:

.. raw:: html

	<a name="report_redundant_bytes"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| report_redundant_bytes | bool | true    |
+------------------------+------+---------+

if this is true, the number of redundant bytes is sent to the
tracker

.. _listen_system_port_fallback:

.. raw:: html

	<a name="listen_system_port_fallback"></a>

+-----------------------------+------+---------+
| name                        | type | default |
+=============================+======+=========+
| listen_system_port_fallback | bool | true    |
+-----------------------------+------+---------+

if this is true, libtorrent will fall back to listening on a port
chosen by the operating system (i.e. binding to port 0). If a
failure is preferred, set this to false.

.. _use_disk_cache_pool:

.. raw:: html

	<a name="use_disk_cache_pool"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| use_disk_cache_pool | bool | false   |
+---------------------+------+---------+

``use_disk_cache_pool`` enables using a pool allocator for disk
cache blocks. Enabling it makes the cache perform better at high
throughput. It also makes the cache less likely and slower at
returning memory back to the system, once allocated.

.. _announce_crypto_support:

.. raw:: html

	<a name="announce_crypto_support"></a>

+-------------------------+------+---------+
| name                    | type | default |
+=========================+======+=========+
| announce_crypto_support | bool | true    |
+-------------------------+------+---------+

when this is true, and incoming encrypted connections are enabled,
&supportcrypt=1 is included in http tracker announces

.. _enable_upnp:

.. raw:: html

	<a name="enable_upnp"></a>

+-------------+------+---------+
| name        | type | default |
+=============+======+=========+
| enable_upnp | bool | true    |
+-------------+------+---------+

Starts and stops the UPnP service. When started, the listen port
and the DHT port are attempted to be forwarded on local UPnP router
devices.

The upnp object returned by ``start_upnp()`` can be used to add and
remove arbitrary port mappings. Mapping status is returned through
the portmap_alert and the portmap_error_alert. The object will be
valid until ``stop_upnp()`` is called. See upnp-and-nat-pmp_.

.. _enable_natpmp:

.. raw:: html

	<a name="enable_natpmp"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| enable_natpmp | bool | true    |
+---------------+------+---------+

Starts and stops the NAT-PMP service. When started, the listen port
and the DHT port are attempted to be forwarded on the router
through NAT-PMP.

The natpmp object returned by ``start_natpmp()`` can be used to add
and remove arbitrary port mappings. Mapping status is returned
through the portmap_alert and the portmap_error_alert. The object
will be valid until ``stop_natpmp()`` is called. See
upnp-and-nat-pmp_.

.. _enable_lsd:

.. raw:: html

	<a name="enable_lsd"></a>

+------------+------+---------+
| name       | type | default |
+============+======+=========+
| enable_lsd | bool | true    |
+------------+------+---------+

Starts and stops Local Service Discovery. This service will
broadcast the infohashes of all the non-private torrents on the
local network to look for peers on the same swarm within multicast
reach.

.. _enable_dht:

.. raw:: html

	<a name="enable_dht"></a>

+------------+------+---------+
| name       | type | default |
+============+======+=========+
| enable_dht | bool | true    |
+------------+------+---------+

starts the dht node and makes the trackerless service available to
torrents.

.. _prefer_rc4:

.. raw:: html

	<a name="prefer_rc4"></a>

+------------+------+---------+
| name       | type | default |
+============+======+=========+
| prefer_rc4 | bool | false   |
+------------+------+---------+

if the allowed encryption level is both, setting this to true will
prefer rc4 if both methods are offered, plaintext otherwise

.. _proxy_hostnames:

.. raw:: html

	<a name="proxy_hostnames"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| proxy_hostnames | bool | true    |
+-----------------+------+---------+

if true, hostname lookups are done via the configured proxy (if
any). This is only supported by SOCKS5 and HTTP.

.. _proxy_peer_connections:

.. raw:: html

	<a name="proxy_peer_connections"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| proxy_peer_connections | bool | true    |
+------------------------+------+---------+

if true, peer connections are made (and accepted) over the
configured proxy, if any.

.. _auto_sequential:

.. raw:: html

	<a name="auto_sequential"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| auto_sequential | bool | true    |
+-----------------+------+---------+

if this setting is true, torrents with a very high availability of
pieces (and seeds) are downloaded sequentially. This is more
efficient for the disk I/O. With many seeds, the download order is
unlikely to matter anyway

.. _tracker_completion_timeout:

.. raw:: html

	<a name="tracker_completion_timeout"></a>

+----------------------------+------+---------+
| name                       | type | default |
+============================+======+=========+
| tracker_completion_timeout | int  | 30      |
+----------------------------+------+---------+

``tracker_completion_timeout`` is the number of seconds the tracker
connection will wait from when it sent the request until it
considers the tracker to have timed-out. Default value is 60
seconds.

.. _tracker_receive_timeout:

.. raw:: html

	<a name="tracker_receive_timeout"></a>

+-------------------------+------+---------+
| name                    | type | default |
+=========================+======+=========+
| tracker_receive_timeout | int  | 10      |
+-------------------------+------+---------+

``tracker_receive_timeout`` is the number of seconds to wait to
receive any data from the tracker. If no data is received for this
number of seconds, the tracker will be considered as having timed
out. If a tracker is down, this is the kind of timeout that will
occur.

.. _stop_tracker_timeout:

.. raw:: html

	<a name="stop_tracker_timeout"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| stop_tracker_timeout | int  | 5       |
+----------------------+------+---------+

the time to wait when sending a stopped message before considering
a tracker to have timed out. this is usually shorter, to make the
client quit faster

.. _tracker_maximum_response_length:

.. raw:: html

	<a name="tracker_maximum_response_length"></a>

+---------------------------------+------+-----------+
| name                            | type | default   |
+=================================+======+===========+
| tracker_maximum_response_length | int  | 1024*1024 |
+---------------------------------+------+-----------+

this is the maximum number of bytes in a tracker response. If a
response size passes this number of bytes it will be rejected and
the connection will be closed. On gzipped responses this size is
measured on the uncompressed data. So, if you get 20 bytes of gzip
response that'll expand to 2 megabytes, it will be interrupted
before the entire response has been uncompressed (assuming the
limit is lower than 2 megs).

.. _piece_timeout:

.. raw:: html

	<a name="piece_timeout"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| piece_timeout | int  | 20      |
+---------------+------+---------+

the number of seconds from a request is sent until it times out if
no piece response is returned.

.. _request_timeout:

.. raw:: html

	<a name="request_timeout"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| request_timeout | int  | 60      |
+-----------------+------+---------+

the number of seconds one block (16kB) is expected to be received
within. If it's not, the block is requested from a different peer

.. _request_queue_time:

.. raw:: html

	<a name="request_queue_time"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| request_queue_time | int  | 3       |
+--------------------+------+---------+

the length of the request queue given in the number of seconds it
should take for the other end to send all the pieces. i.e. the
actual number of requests depends on the download rate and this
number.

.. _max_allowed_in_request_queue:

.. raw:: html

	<a name="max_allowed_in_request_queue"></a>

+------------------------------+------+---------+
| name                         | type | default |
+==============================+======+=========+
| max_allowed_in_request_queue | int  | 500     |
+------------------------------+------+---------+

the number of outstanding block requests a peer is allowed to queue
up in the client. If a peer sends more requests than this (before
the first one has been sent) the last request will be dropped. the
higher this is, the faster upload speeds the client can get to a
single peer.

.. _max_out_request_queue:

.. raw:: html

	<a name="max_out_request_queue"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| max_out_request_queue | int  | 500     |
+-----------------------+------+---------+

``max_out_request_queue`` is the maximum number of outstanding
requests to send to a peer. This limit takes precedence over
``request_queue_time``. i.e. no matter the download speed, the
number of outstanding requests will never exceed this limit.

.. _whole_pieces_threshold:

.. raw:: html

	<a name="whole_pieces_threshold"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| whole_pieces_threshold | int  | 20      |
+------------------------+------+---------+

if a whole piece can be downloaded in this number of seconds, or
less, the peer_connection will prefer to request whole pieces at a
time from this peer. The benefit of this is to better utilize disk
caches by doing localized accesses and also to make it easier to
identify bad peers if a piece fails the hash check.

.. _peer_timeout:

.. raw:: html

	<a name="peer_timeout"></a>

+--------------+------+---------+
| name         | type | default |
+==============+======+=========+
| peer_timeout | int  | 120     |
+--------------+------+---------+

``peer_timeout`` is the number of seconds the peer connection
should wait (for any activity on the peer connection) before
closing it due to time out. This defaults to 120 seconds, since
that's what's specified in the protocol specification. After half
the time out, a keep alive message is sent.

.. _urlseed_timeout:

.. raw:: html

	<a name="urlseed_timeout"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| urlseed_timeout | int  | 20      |
+-----------------+------+---------+

same as peer_timeout, but only applies to url-seeds. this is
usually set lower, because web servers are expected to be more
reliable.

.. _urlseed_pipeline_size:

.. raw:: html

	<a name="urlseed_pipeline_size"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| urlseed_pipeline_size | int  | 5       |
+-----------------------+------+---------+

controls the pipelining size of url-seeds. i.e. the number of HTTP
request to keep outstanding before waiting for the first one to
complete. It's common for web servers to limit this to a relatively
low number, like 5

.. _urlseed_wait_retry:

.. raw:: html

	<a name="urlseed_wait_retry"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| urlseed_wait_retry | int  | 30      |
+--------------------+------+---------+

time to wait until a new retry of a web seed takes place

.. _file_pool_size:

.. raw:: html

	<a name="file_pool_size"></a>

+----------------+------+---------+
| name           | type | default |
+================+======+=========+
| file_pool_size | int  | 40      |
+----------------+------+---------+

sets the upper limit on the total number of files this session will
keep open. The reason why files are left open at all is that some
anti virus software hooks on every file close, and scans the file
for viruses. deferring the closing of the files will be the
difference between a usable system and a completely hogged down
system. Most operating systems also has a limit on the total number
of file descriptors a process may have open. It is usually a good
idea to find this limit and set the number of connections and the
number of files limits so their sum is slightly below it.

.. _max_failcount:

.. raw:: html

	<a name="max_failcount"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| max_failcount | int  | 3       |
+---------------+------+---------+

``max_failcount`` is the maximum times we try to connect to a peer
before stop connecting again. If a peer succeeds, the failcounter
is reset. If a peer is retrieved from a peer source (other than
DHT) the failcount is decremented by one, allowing another try.

.. _min_reconnect_time:

.. raw:: html

	<a name="min_reconnect_time"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| min_reconnect_time | int  | 60      |
+--------------------+------+---------+

the number of seconds to wait to reconnect to a peer. this time is
multiplied with the failcount.

.. _peer_connect_timeout:

.. raw:: html

	<a name="peer_connect_timeout"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| peer_connect_timeout | int  | 15      |
+----------------------+------+---------+

``peer_connect_timeout`` the number of seconds to wait after a
connection attempt is initiated to a peer until it is considered as
having timed out. This setting is especially important in case the
number of half-open connections are limited, since stale half-open
connection may delay the connection of other peers considerably.

.. _connection_speed:

.. raw:: html

	<a name="connection_speed"></a>

+------------------+------+---------+
| name             | type | default |
+==================+======+=========+
| connection_speed | int  | 6       |
+------------------+------+---------+

``connection_speed`` is the number of connection attempts that are
made per second. If a number < 0 is specified, it will default to
200 connections per second. If 0 is specified, it means don't make
outgoing connections at all.

.. _inactivity_timeout:

.. raw:: html

	<a name="inactivity_timeout"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| inactivity_timeout | int  | 600     |
+--------------------+------+---------+

if a peer is uninteresting and uninterested for longer than this
number of seconds, it will be disconnected. default is 10 minutes

.. _unchoke_interval:

.. raw:: html

	<a name="unchoke_interval"></a>

+------------------+------+---------+
| name             | type | default |
+==================+======+=========+
| unchoke_interval | int  | 15      |
+------------------+------+---------+

``unchoke_interval`` is the number of seconds between
chokes/unchokes. On this interval, peers are re-evaluated for being
choked/unchoked. This is defined as 30 seconds in the protocol, and
it should be significantly longer than what it takes for TCP to
ramp up to it's max rate.

.. _optimistic_unchoke_interval:

.. raw:: html

	<a name="optimistic_unchoke_interval"></a>

+-----------------------------+------+---------+
| name                        | type | default |
+=============================+======+=========+
| optimistic_unchoke_interval | int  | 30      |
+-----------------------------+------+---------+

``optimistic_unchoke_interval`` is the number of seconds between
each *optimistic* unchoke. On this timer, the currently
optimistically unchoked peer will change.

.. _num_want:

.. raw:: html

	<a name="num_want"></a>

+----------+------+---------+
| name     | type | default |
+==========+======+=========+
| num_want | int  | 200     |
+----------+------+---------+

``num_want`` is the number of peers we want from each tracker
request. It defines what is sent as the ``&num_want=`` parameter to
the tracker.

.. _initial_picker_threshold:

.. raw:: html

	<a name="initial_picker_threshold"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| initial_picker_threshold | int  | 4       |
+--------------------------+------+---------+

``initial_picker_threshold`` specifies the number of pieces we need
before we switch to rarest first picking. This defaults to 4, which
means the 4 first pieces in any torrent are picked at random, the
following pieces are picked in rarest first order.

.. _allowed_fast_set_size:

.. raw:: html

	<a name="allowed_fast_set_size"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| allowed_fast_set_size | int  | 10      |
+-----------------------+------+---------+

the number of allowed pieces to send to peers that supports the
fast extensions

.. _suggest_mode:

.. raw:: html

	<a name="suggest_mode"></a>

+--------------+------+-------------------------------------+
| name         | type | default                             |
+==============+======+=====================================+
| suggest_mode | int  | settings_pack::no_piece_suggestions |
+--------------+------+-------------------------------------+

``suggest_mode`` controls whether or not libtorrent will send out
suggest messages to create a bias of its peers to request certain
pieces. The modes are:

* ``no_piece_suggestsions`` which is the default and will not send
  out suggest messages.
* ``suggest_read_cache`` which will send out suggest messages for
  the most recent pieces that are in the read cache.

.. _max_queued_disk_bytes:

.. raw:: html

	<a name="max_queued_disk_bytes"></a>

+-----------------------+------+-------------+
| name                  | type | default     |
+=======================+======+=============+
| max_queued_disk_bytes | int  | 1024 * 1024 |
+-----------------------+------+-------------+

``max_queued_disk_bytes`` is the number maximum number of bytes, to
be written to disk, that can wait in the disk I/O thread queue.
This queue is only for waiting for the disk I/O thread to receive
the job and either write it to disk or insert it in the write
cache. When this limit is reached, the peer connections will stop
reading data from their sockets, until the disk thread catches up.
Setting this too low will severly limit your download rate.

.. _handshake_timeout:

.. raw:: html

	<a name="handshake_timeout"></a>

+-------------------+------+---------+
| name              | type | default |
+===================+======+=========+
| handshake_timeout | int  | 10      |
+-------------------+------+---------+

the number of seconds to wait for a handshake response from a peer.
If no response is received within this time, the peer is
disconnected.

.. _send_buffer_low_watermark:

.. _send_buffer_watermark:

.. _send_buffer_watermark_factor:

.. raw:: html

	<a name="send_buffer_low_watermark"></a>
	<a name="send_buffer_watermark"></a>
	<a name="send_buffer_watermark_factor"></a>

+------------------------------+------+------------+
| name                         | type | default    |
+==============================+======+============+
| send_buffer_low_watermark    | int  | 10 * 1024  |
+------------------------------+------+------------+
| send_buffer_watermark        | int  | 500 * 1024 |
+------------------------------+------+------------+
| send_buffer_watermark_factor | int  | 50         |
+------------------------------+------+------------+

``send_buffer_low_watermark`` the minimum send buffer target size
(send buffer includes bytes pending being read from disk). For good
and snappy seeding performance, set this fairly high, to at least
fit a few blocks. This is essentially the initial window size which
will determine how fast we can ramp up the send rate

if the send buffer has fewer bytes than ``send_buffer_watermark``,
we'll read another 16kB block onto it. If set too small, upload
rate capacity will suffer. If set too high, memory will be wasted.
The actual watermark may be lower than this in case the upload rate
is low, this is the upper limit.

the current upload rate to a peer is multiplied by this factor to
get the send buffer watermark. The factor is specified as a
percentage. i.e. 50 -> 0.5 This product is clamped to the
``send_buffer_watermark`` setting to not exceed the max. For high
speed upload, this should be set to a greater value than 100. For
high capacity connections, setting this higher can improve upload
performance and disk throughput. Setting it too high may waste RAM
and create a bias towards read jobs over write jobs.

.. _choking_algorithm:

.. _seed_choking_algorithm:

.. raw:: html

	<a name="choking_algorithm"></a>
	<a name="seed_choking_algorithm"></a>

+------------------------+------+-----------------------------------+
| name                   | type | default                           |
+========================+======+===================================+
| choking_algorithm      | int  | settings_pack::fixed_slots_choker |
+------------------------+------+-----------------------------------+
| seed_choking_algorithm | int  | settings_pack::round_robin        |
+------------------------+------+-----------------------------------+

``choking_algorithm`` specifies which algorithm to use to determine
which peers to unchoke.

The options for choking algorithms are:

* ``fixed_slots_choker`` is the traditional choker with a fixed
  number of unchoke slots (as specified by
  ``session::set_max_uploads()``).

* ``rate_based_choker`` opens up unchoke slots based on the upload
  rate achieved to peers. The more slots that are opened, the
  marginal upload rate required to open up another slot increases.

* ``bittyrant_choker`` attempts to optimize download rate by
  finding the reciprocation rate of each peer individually and
  prefers peers that gives the highest *return on investment*. It
  still allocates all upload capacity, but shuffles it around to
  the best peers first. For this choker to be efficient, you need
  to set a global upload rate limit
  (``session::set_upload_rate_limit()``). For more information
  about this choker, see the paper_. This choker is not fully
  implemented nor tested.

.. _paper: http://bittyrant.cs.washington.edu/#papers

``seed_choking_algorithm`` controls the seeding unchoke behavior.
The available options are:

* ``round_robin`` which round-robins the peers that are unchoked
  when seeding. This distributes the upload bandwidht uniformly and
  fairly. It minimizes the ability for a peer to download everything
  without redistributing it.

* ``fastest_upload`` unchokes the peers we can send to the fastest.
  This might be a bit more reliable in utilizing all available
  capacity.

* ``anti_leech`` prioritizes peers who have just started or are
  just about to finish the download. The intention is to force
  peers in the middle of the download to trade with each other.

.. _cache_size:

.. _cache_buffer_chunk_size:

.. _cache_expiry:

.. raw:: html

	<a name="cache_size"></a>
	<a name="cache_buffer_chunk_size"></a>
	<a name="cache_expiry"></a>

+-------------------------+------+---------+
| name                    | type | default |
+=========================+======+=========+
| cache_size              | int  | 1024    |
+-------------------------+------+---------+
| cache_buffer_chunk_size | int  | 0       |
+-------------------------+------+---------+
| cache_expiry            | int  | 300     |
+-------------------------+------+---------+

``cache_size`` is the disk write and read  cache. It is specified
in units of 16 KiB blocks. Buffers that are part of a peer's send
or receive buffer also count against this limit. Send and receive
buffers will never be denied to be allocated, but they will cause
the actual cached blocks to be flushed or evicted. If this is set
to -1, the cache size is automatically set to the amount of
physical RAM available in the machine divided by 8. If the amount
of physical RAM cannot be determined, it's set to 1024 (= 16 MiB).

Disk buffers are allocated using a pool allocator, the number of
blocks that are allocated at a time when the pool needs to grow can
be specified in ``cache_buffer_chunk_size``. Lower numbers saves
memory at the expense of more heap allocations. If it is set to 0,
the effective chunk size is proportional to the total cache size,
attempting to strike a good balance between performance and memory
usage. It defaults to 0. ``cache_expiry`` is the number of seconds
from the last cached write to a piece in the write cache, to when
it's forcefully flushed to disk. Default is 60 second.

.. _explicit_cache_interval:

.. raw:: html

	<a name="explicit_cache_interval"></a>

+-------------------------+------+---------+
| name                    | type | default |
+=========================+======+=========+
| explicit_cache_interval | int  | 30      |
+-------------------------+------+---------+

``explicit_cache_interval`` is the number of seconds in between
each refresh of a part of the explicit read cache. Torrents take
turns in refreshing and this is the time in between each torrent
refresh. Refreshing a torrent's explicit read cache means scanning
all pieces and picking a random set of the rarest ones. There is an
affinity to pick pieces that are already in the cache, so that
subsequent refreshes only swaps in pieces that are rarer than
whatever is in the cache at the time.

.. _disk_io_write_mode:

.. _disk_io_read_mode:

.. raw:: html

	<a name="disk_io_write_mode"></a>
	<a name="disk_io_read_mode"></a>

+--------------------+------+--------------------------------+
| name               | type | default                        |
+====================+======+================================+
| disk_io_write_mode | int  | settings_pack::enable_os_cache |
+--------------------+------+--------------------------------+
| disk_io_read_mode  | int  | settings_pack::enable_os_cache |
+--------------------+------+--------------------------------+

determines how files are opened when they're in read only mode
versus read and write mode. The options are:

enable_os_cache
  This is the default and files are opened normally, with the OS
  caching reads and writes.
disable_os_cache
  This opens all files in no-cache mode. This corresponds to the
  OS not letting blocks for the files linger in the cache. This
  makes sense in order to avoid the bittorrent client to
  potentially evict all other processes' cache by simply handling
  high throughput and large files. If libtorrent's read cache is
  disabled, enabling this may reduce performance.

One reason to disable caching is that it may help the operating
system from growing its file cache indefinitely.

.. _outgoing_port:

.. _num_outgoing_ports:

.. raw:: html

	<a name="outgoing_port"></a>
	<a name="num_outgoing_ports"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| outgoing_port      | int  | 0       |
+--------------------+------+---------+
| num_outgoing_ports | int  | 0       |
+--------------------+------+---------+

this is the first port to use for binding outgoing connections to.
This is useful for users that have routers that allow QoS settings
based on local port. when binding outgoing connections to specific
ports, ``num_outgoing_ports`` is the size of the range. It should
be more than a few

.. warning:: setting outgoing ports will limit the ability to keep
   multiple connections to the same client, even for different
   torrents. It is not recommended to change this setting. Its main
   purpose is to use as an escape hatch for cheap routers with QoS
   capability but can only classify flows based on port numbers.

It is a range instead of a single port because of the problems with
failing to reconnect to peers if a previous socket to that peer and
port is in ``TIME_WAIT`` state.

.. _peer_tos:

.. raw:: html

	<a name="peer_tos"></a>

+----------+------+---------+
| name     | type | default |
+==========+======+=========+
| peer_tos | int  | 0       |
+----------+------+---------+

``peer_tos`` determines the TOS byte set in the IP header of every
packet sent to peers (including web seeds). The default value for
this is ``0x0`` (no marking). One potentially useful TOS mark is
``0x20``, this represents the *QBone scavenger service*. For more
details, see QBSS_.

.. _`QBSS`: http://qbone.internet2.edu/qbss/

.. _active_downloads:

.. _active_seeds:

.. _active_dht_limit:

.. _active_tracker_limit:

.. _active_lsd_limit:

.. _active_limit:

.. _active_loaded_limit:

.. raw:: html

	<a name="active_downloads"></a>
	<a name="active_seeds"></a>
	<a name="active_dht_limit"></a>
	<a name="active_tracker_limit"></a>
	<a name="active_lsd_limit"></a>
	<a name="active_limit"></a>
	<a name="active_loaded_limit"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| active_downloads     | int  | 3       |
+----------------------+------+---------+
| active_seeds         | int  | 5       |
+----------------------+------+---------+
| active_dht_limit     | int  | 88      |
+----------------------+------+---------+
| active_tracker_limit | int  | 1600    |
+----------------------+------+---------+
| active_lsd_limit     | int  | 60      |
+----------------------+------+---------+
| active_limit         | int  | 15      |
+----------------------+------+---------+
| active_loaded_limit  | int  | 100     |
+----------------------+------+---------+

for auto managed torrents, these are the limits they are subject
to. If there are too many torrents some of the auto managed ones
will be paused until some slots free up. ``active_downloads`` and
``active_seeds`` controls how many active seeding and downloading
torrents the queuing mechanism allows. The target number of active
torrents is ``min(active_downloads + active_seeds, active_limit)``.
``active_downloads`` and ``active_seeds`` are upper limits on the
number of downloading torrents and seeding torrents respectively.
Setting the value to -1 means unlimited.

For example if there are 10 seeding torrents and 10 downloading
torrents, and ``active_downloads`` is 4 and ``active_seeds`` is 4,
there will be 4 seeds active and 4 downloading torrents. If the
settings are ``active_downloads`` = 2 and ``active_seeds`` = 4,
then there will be 2 downloading torrents and 4 seeding torrents
active. Torrents that are not auto managed are not counted against
these limits.

``active_limit`` is a hard limit on the number of active torrents.
This applies even to slow torrents.

``active_dht_limit`` is the max number of torrents to announce to
the DHT. By default this is set to 88, which is no more than one
DHT announce every 10 seconds.

``active_tracker_limit`` is the max number of torrents to announce
to their trackers. By default this is 360, which is no more than
one announce every 5 seconds.

``active_lsd_limit`` is the max number of torrents to announce to
the local network over the local service discovery protocol. By
default this is 80, which is no more than one announce every 5
seconds (assuming the default announce interval of 5 minutes).

You can have more torrents *active*, even though they are not
announced to the DHT, lsd or their tracker. If some peer knows
about you for any reason and tries to connect, it will still be
accepted, unless the torrent is paused, which means it won't accept
any connections.

``active_loaded_limit`` is the number of torrents that are allowed
to be *loaded* at any given time. Note that a torrent can be active
even though it's not loaded. if an unloaded torrents finds a peer
that wants to access it, the torrent will be loaded on demand,
using a user-supplied callback function. If the feature of
unloading torrents is not enabled, this setting have no effect. If
this limit is set to 0, it means unlimited. For more information,
see dynamic-loading-of-torrent-files_.

.. _auto_manage_interval:

.. raw:: html

	<a name="auto_manage_interval"></a>

+----------------------+------+---------+
| name                 | type | default |
+======================+======+=========+
| auto_manage_interval | int  | 30      |
+----------------------+------+---------+

``auto_manage_interval`` is the number of seconds between the
torrent queue is updated, and rotated.

.. _seed_time_limit:

.. raw:: html

	<a name="seed_time_limit"></a>

+-----------------+------+--------------+
| name            | type | default      |
+=================+======+==============+
| seed_time_limit | int  | 24 * 60 * 60 |
+-----------------+------+--------------+

this is the limit on the time a torrent has been an active seed
(specified in seconds) before it is considered having met the seed
limit criteria. See queuing_.

.. _auto_scrape_interval:

.. _auto_scrape_min_interval:

.. raw:: html

	<a name="auto_scrape_interval"></a>
	<a name="auto_scrape_min_interval"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| auto_scrape_interval     | int  | 1800    |
+--------------------------+------+---------+
| auto_scrape_min_interval | int  | 300     |
+--------------------------+------+---------+

``auto_scrape_interval`` is the number of seconds between scrapes
of queued torrents (auto managed and paused torrents). Auto managed
torrents that are paused, are scraped regularly in order to keep
track of their downloader/seed ratio. This ratio is used to
determine which torrents to seed and which to pause.

``auto_scrape_min_interval`` is the minimum number of seconds
between any automatic scrape (regardless of torrent). In case there
are a large number of paused auto managed torrents, this puts a
limit on how often a scrape request is sent.

.. _max_peerlist_size:

.. _max_paused_peerlist_size:

.. raw:: html

	<a name="max_peerlist_size"></a>
	<a name="max_paused_peerlist_size"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| max_peerlist_size        | int  | 3000    |
+--------------------------+------+---------+
| max_paused_peerlist_size | int  | 1000    |
+--------------------------+------+---------+

``max_peerlist_size`` is the maximum number of peers in the list of
known peers. These peers are not necessarily connected, so this
number should be much greater than the maximum number of connected
peers. Peers are evicted from the cache when the list grows passed
90% of this limit, and once the size hits the limit, peers are no
longer added to the list. If this limit is set to 0, there is no
limit on how many peers we'll keep in the peer list.

``max_paused_peerlist_size`` is the max peer list size used for
torrents that are paused. This default to the same as
``max_peerlist_size``, but can be used to save memory for paused
torrents, since it's not as important for them to keep a large peer
list.

.. _min_announce_interval:

.. raw:: html

	<a name="min_announce_interval"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| min_announce_interval | int  | 5 * 60  |
+-----------------------+------+---------+

this is the minimum allowed announce interval for a tracker. This
is specified in seconds and is used as a sanity check on what is
returned from a tracker. It mitigates hammering misconfigured
trackers.

.. _auto_manage_startup:

.. raw:: html

	<a name="auto_manage_startup"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| auto_manage_startup | int  | 60      |
+---------------------+------+---------+

this is the number of seconds a torrent is considered active after
it was started, regardless of upload and download speed. This is so
that newly started torrents are not considered inactive until they
have a fair chance to start downloading.

.. _seeding_piece_quota:

.. raw:: html

	<a name="seeding_piece_quota"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| seeding_piece_quota | int  | 20      |
+---------------------+------+---------+

``seeding_piece_quota`` is the number of pieces to send to a peer,
when seeding, before rotating in another peer to the unchoke set.
It defaults to 3 pieces, which means that when seeding, any peer
we've sent more than this number of pieces to will be unchoked in
favour of a choked peer.

.. _max_rejects:

.. raw:: html

	<a name="max_rejects"></a>

+-------------+------+---------+
| name        | type | default |
+=============+======+=========+
| max_rejects | int  | 50      |
+-------------+------+---------+

TODO: deprecate this
``max_rejects`` is the number of piece requests we will reject in a
row while a peer is choked before the peer is considered abusive
and is disconnected.

.. _recv_socket_buffer_size:

.. _send_socket_buffer_size:

.. raw:: html

	<a name="recv_socket_buffer_size"></a>
	<a name="send_socket_buffer_size"></a>

+-------------------------+------+---------+
| name                    | type | default |
+=========================+======+=========+
| recv_socket_buffer_size | int  | 0       |
+-------------------------+------+---------+
| send_socket_buffer_size | int  | 0       |
+-------------------------+------+---------+

``recv_socket_buffer_size`` and ``send_socket_buffer_size``
specifies the buffer sizes set on peer sockets. 0 (which is the
default) means the OS default (i.e. don't change the buffer sizes).
The socket buffer sizes are changed using setsockopt() with
SOL_SOCKET/SO_RCVBUF and SO_SNDBUFFER.

.. _file_checks_delay_per_block:

.. raw:: html

	<a name="file_checks_delay_per_block"></a>

+-----------------------------+------+---------+
| name                        | type | default |
+=============================+======+=========+
| file_checks_delay_per_block | int  | 0       |
+-----------------------------+------+---------+

``file_checks_delay_per_block`` is the number of milliseconds to
sleep in between disk read operations when checking torrents. This
defaults to 0, but can be set to higher numbers to slow down the
rate at which data is read from the disk while checking. This may
be useful for background tasks that doesn't matter if they take a
bit longer, as long as they leave disk I/O time for other
processes.

.. _read_cache_line_size:

.. _write_cache_line_size:

.. raw:: html

	<a name="read_cache_line_size"></a>
	<a name="write_cache_line_size"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| read_cache_line_size  | int  | 32      |
+-----------------------+------+---------+
| write_cache_line_size | int  | 16      |
+-----------------------+------+---------+

``read_cache_line_size`` is the number of blocks to read into the
read cache when a read cache miss occurs. Setting this to 0 is
essentially the same thing as disabling read cache. The number of
blocks read into the read cache is always capped by the piece
boundry.

When a piece in the write cache has ``write_cache_line_size``
contiguous blocks in it, they will be flushed. Setting this to 1
effectively disables the write cache.

.. _optimistic_disk_retry:

.. raw:: html

	<a name="optimistic_disk_retry"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| optimistic_disk_retry | int  | 10 * 60 |
+-----------------------+------+---------+

``optimistic_disk_retry`` is the number of seconds from a disk
write errors occur on a torrent until libtorrent will take it out
of the upload mode, to test if the error condition has been fixed.

libtorrent will only do this automatically for auto managed
torrents.

You can explicitly take a torrent out of upload only mode using
set_upload_mode().

.. _max_suggest_pieces:

.. raw:: html

	<a name="max_suggest_pieces"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| max_suggest_pieces | int  | 10      |
+--------------------+------+---------+

``max_suggest_pieces`` is the max number of suggested piece indices
received from a peer that's remembered. If a peer floods suggest
messages, this limit prevents libtorrent from using too much RAM.
It defaults to 10.

.. _local_service_announce_interval:

.. raw:: html

	<a name="local_service_announce_interval"></a>

+---------------------------------+------+---------+
| name                            | type | default |
+=================================+======+=========+
| local_service_announce_interval | int  | 5 * 60  |
+---------------------------------+------+---------+

``local_service_announce_interval`` is the time between local
network announces for a torrent. By default, when local service
discovery is enabled a torrent announces itself every 5 minutes.
This interval is specified in seconds.

.. _dht_announce_interval:

.. raw:: html

	<a name="dht_announce_interval"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| dht_announce_interval | int  | 15 * 60 |
+-----------------------+------+---------+

``dht_announce_interval`` is the number of seconds between
announcing torrents to the distributed hash table (DHT).

.. _udp_tracker_token_expiry:

.. raw:: html

	<a name="udp_tracker_token_expiry"></a>

+--------------------------+------+---------+
| name                     | type | default |
+==========================+======+=========+
| udp_tracker_token_expiry | int  | 60      |
+--------------------------+------+---------+

``udp_tracker_token_expiry`` is the number of seconds libtorrent
will keep UDP tracker connection tokens around for. This is
specified to be 60 seconds, and defaults to that. The higher this
value is, the fewer packets have to be sent to the UDP tracker. In
order for higher values to work, the tracker needs to be configured
to match the expiration time for tokens.

.. _default_cache_min_age:

.. raw:: html

	<a name="default_cache_min_age"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| default_cache_min_age | int  | 1       |
+-----------------------+------+---------+

``default_cache_min_age`` is the minimum number of seconds any read
cache line is kept in the cache. This defaults to one second but
may be greater if ``guided_read_cache`` is enabled. Having a lower
bound on the time a cache line stays in the cache is an attempt
to avoid swapping the same pieces in and out of the cache in case
there is a shortage of spare cache space.

.. _num_optimistic_unchoke_slots:

.. raw:: html

	<a name="num_optimistic_unchoke_slots"></a>

+------------------------------+------+---------+
| name                         | type | default |
+==============================+======+=========+
| num_optimistic_unchoke_slots | int  | 0       |
+------------------------------+------+---------+

``num_optimistic_unchoke_slots`` is the number of optimistic
unchoke slots to use. It defaults to 0, which means automatic.
Having a higher number of optimistic unchoke slots mean you will
find the good peers faster but with the trade-off to use up more
bandwidth. When this is set to 0, libtorrent opens up 20% of your
allowed upload slots as optimistic unchoke slots.

.. _default_est_reciprocation_rate:

.. _increase_est_reciprocation_rate:

.. _decrease_est_reciprocation_rate:

.. raw:: html

	<a name="default_est_reciprocation_rate"></a>
	<a name="increase_est_reciprocation_rate"></a>
	<a name="decrease_est_reciprocation_rate"></a>

+---------------------------------+------+---------+
| name                            | type | default |
+=================================+======+=========+
| default_est_reciprocation_rate  | int  | 16000   |
+---------------------------------+------+---------+
| increase_est_reciprocation_rate | int  | 20      |
+---------------------------------+------+---------+
| decrease_est_reciprocation_rate | int  | 3       |
+---------------------------------+------+---------+

``default_est_reciprocation_rate`` is the assumed reciprocation
rate from peers when using the BitTyrant choker. This defaults to
14 kiB/s. If set too high, you will over-estimate your peers and be
more altruistic while finding the true reciprocation rate, if it's
set too low, you'll be too stingy and waste finding the true
reciprocation rate.

``increase_est_reciprocation_rate`` specifies how many percent the
extimated reciprocation rate should be increased by each unchoke
interval a peer is still choking us back. This defaults to 20%.
This only applies to the BitTyrant choker.

``decrease_est_reciprocation_rate`` specifies how many percent the
estimated reciprocation rate should be decreased by each unchoke
interval a peer unchokes us. This default to 3%. This only applies
to the BitTyrant choker.

.. _max_pex_peers:

.. raw:: html

	<a name="max_pex_peers"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| max_pex_peers | int  | 50      |
+---------------+------+---------+

the max number of peers we accept from pex messages from a single
peer. this limits the number of concurrent peers any of our peers
claims to be connected to. If they clain to be connected to more
than this, we'll ignore any peer that exceeds this limit

.. _tick_interval:

.. raw:: html

	<a name="tick_interval"></a>

+---------------+------+---------+
| name          | type | default |
+===============+======+=========+
| tick_interval | int  | 500     |
+---------------+------+---------+

``tick_interval`` specifies the number of milliseconds between
internal ticks. This is the frequency with which bandwidth quota is
distributed to peers. It should not be more than one second (i.e.
1000 ms). Setting this to a low value (around 100) means higher
resolution bandwidth quota distribution, setting it to a higher
value saves CPU cycles.

.. _share_mode_target:

.. raw:: html

	<a name="share_mode_target"></a>

+-------------------+------+---------+
| name              | type | default |
+===================+======+=========+
| share_mode_target | int  | 3       |
+-------------------+------+---------+

``share_mode_target`` specifies the target share ratio for share
mode torrents. This defaults to 3, meaning we'll try to upload 3
times as much as we download. Setting this very high, will make it
very conservative and you might end up not downloading anything
ever (and not affecting your share ratio). It does not make any
sense to set this any lower than 2. For instance, if only 3 peers
need to download the rarest piece, it's impossible to download a
single piece and upload it more than 3 times. If the
share_mode_target is set to more than 3, nothing is downloaded.

.. _upload_rate_limit:

.. _download_rate_limit:

.. raw:: html

	<a name="upload_rate_limit"></a>
	<a name="download_rate_limit"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| upload_rate_limit   | int  | 0       |
+---------------------+------+---------+
| download_rate_limit | int  | 0       |
+---------------------+------+---------+

``upload_rate_limit``, ``download_rate_limit``,
``local_upload_rate_limit`` and ``local_download_rate_limit`` sets
the session-global limits of upload and download rate limits, in
bytes per second. The local rates refer to peers on the local
network. By default peers on the local network are not rate
limited.

These rate limits are only used for local peers (peers within the
same subnet as the client itself) and it is only used when
``ignore_limits_on_local_network`` is set to true (which it is by
default). These rate limits default to unthrottled, but can be
useful in case you want to treat local peers preferentially, but
not quite unthrottled.

A value of 0 means unlimited.

.. _dht_upload_rate_limit:

.. raw:: html

	<a name="dht_upload_rate_limit"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| dht_upload_rate_limit | int  | 4000    |
+-----------------------+------+---------+

``dht_upload_rate_limit`` sets the rate limit on the DHT. This is
specified in bytes per second and defaults to 4000. For busy boxes
with lots of torrents that requires more DHT traffic, this should
be raised.

.. _unchoke_slots_limit:

.. raw:: html

	<a name="unchoke_slots_limit"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| unchoke_slots_limit | int  | 8       |
+---------------------+------+---------+

``unchoke_slots_limit`` is the max number of unchoked peers in the
session. The number of unchoke slots may be ignored depending on
what ``choking_algorithm`` is set to.

.. _connections_limit:

.. raw:: html

	<a name="connections_limit"></a>

+-------------------+------+---------+
| name              | type | default |
+===================+======+=========+
| connections_limit | int  | 200     |
+-------------------+------+---------+

``connections_limit`` sets a global limit on the number of
connections opened. The number of connections is set to a hard
minimum of at least two per torrent, so if you set a too low
connections limit, and open too many torrents, the limit will not
be met.

.. _connections_slack:

.. raw:: html

	<a name="connections_slack"></a>

+-------------------+------+---------+
| name              | type | default |
+===================+======+=========+
| connections_slack | int  | 10      |
+-------------------+------+---------+

``connections_slack`` is the the number of incoming connections
exceeding the connection limit to accept in order to potentially
replace existing ones.

.. _utp_target_delay:

.. _utp_gain_factor:

.. _utp_min_timeout:

.. _utp_syn_resends:

.. _utp_fin_resends:

.. _utp_num_resends:

.. _utp_connect_timeout:

.. _utp_loss_multiplier:

.. raw:: html

	<a name="utp_target_delay"></a>
	<a name="utp_gain_factor"></a>
	<a name="utp_min_timeout"></a>
	<a name="utp_syn_resends"></a>
	<a name="utp_fin_resends"></a>
	<a name="utp_num_resends"></a>
	<a name="utp_connect_timeout"></a>
	<a name="utp_loss_multiplier"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| utp_target_delay    | int  | 100     |
+---------------------+------+---------+
| utp_gain_factor     | int  | 3000    |
+---------------------+------+---------+
| utp_min_timeout     | int  | 500     |
+---------------------+------+---------+
| utp_syn_resends     | int  | 2       |
+---------------------+------+---------+
| utp_fin_resends     | int  | 2       |
+---------------------+------+---------+
| utp_num_resends     | int  | 3       |
+---------------------+------+---------+
| utp_connect_timeout | int  | 3000    |
+---------------------+------+---------+
| utp_loss_multiplier | int  | 50      |
+---------------------+------+---------+

``utp_target_delay`` is the target delay for uTP sockets in
milliseconds. A high value will make uTP connections more
aggressive and cause longer queues in the upload bottleneck. It
cannot be too low, since the noise in the measurements would cause
it to send too slow. The default is 50 milliseconds.
``utp_gain_factor`` is the number of bytes the uTP congestion
window can increase at the most in one RTT. This defaults to 300
bytes. If this is set too high, the congestion controller reacts
too hard to noise and will not be stable, if it's set too low, it
will react slow to congestion and not back off as fast.
``utp_min_timeout`` is the shortest allowed uTP socket timeout,
specified in milliseconds. This defaults to 500 milliseconds. The
timeout depends on the RTT of the connection, but is never smaller
than this value. A connection times out when every packet in a
window is lost, or when a packet is lost twice in a row (i.e. the
resent packet is lost as well).

The shorter the timeout is, the faster the connection will recover
from this situation, assuming the RTT is low enough.
``utp_syn_resends`` is the number of SYN packets that are sent (and
timed out) before giving up and closing the socket.
``utp_num_resends`` is the number of times a packet is sent (and
lossed or timed out) before giving up and closing the connection.
``utp_connect_timeout`` is the number of milliseconds of timeout
for the initial SYN packet for uTP connections. For each timed out
packet (in a row), the timeout is doubled. ``utp_loss_multiplier``
controls how the congestion window is changed when a packet loss is
experienced. It's specified as a percentage multiplier for
``cwnd``. By default it's set to 50 (i.e. cut in half). Do not
change this value unless you know what you're doing. Never set it
higher than 100.

.. _mixed_mode_algorithm:

.. raw:: html

	<a name="mixed_mode_algorithm"></a>

+----------------------+------+----------------------------------+
| name                 | type | default                          |
+======================+======+==================================+
| mixed_mode_algorithm | int  | settings_pack::peer_proportional |
+----------------------+------+----------------------------------+

The ``mixed_mode_algorithm`` determines how to treat TCP
connections when there are uTP connections. Since uTP is designed
to yield to TCP, there's an inherent problem when using swarms that
have both TCP and uTP connections. If nothing is done, uTP
connections would often be starved out for bandwidth by the TCP
connections. This mode is ``prefer_tcp``. The ``peer_proportional``
mode simply looks at the current throughput and rate limits all TCP
connections to their proportional share based on how many of the
connections are TCP. This works best if uTP connections are not
rate limited by the global rate limiter (which they aren't by
default).

.. _listen_queue_size:

.. raw:: html

	<a name="listen_queue_size"></a>

+-------------------+------+---------+
| name              | type | default |
+===================+======+=========+
| listen_queue_size | int  | 5       |
+-------------------+------+---------+

``listen_queue_size`` is the value passed in to listen() for the
listen socket. It is the number of outstanding incoming connections
to queue up while we're not actively waiting for a connection to be
accepted. The default is 5 which should be sufficient for any
normal client. If this is a high performance server which expects
to receive a lot of connections, or used in a simulator or test, it
might make sense to raise this number. It will not take affect
until listen_on() is called again (or for the first time).

.. _torrent_connect_boost:

.. raw:: html

	<a name="torrent_connect_boost"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| torrent_connect_boost | int  | 10      |
+-----------------------+------+---------+

``torrent_connect_boost`` is the number of peers to try to connect
to immediately when the first tracker response is received for a
torrent. This is a boost to given to new torrents to accelerate
them starting up. The normal connect scheduler is run once every
second, this allows peers to be connected immediately instead of
waiting for the session tick to trigger connections.

.. _alert_queue_size:

.. raw:: html

	<a name="alert_queue_size"></a>

+------------------+------+---------+
| name             | type | default |
+==================+======+=========+
| alert_queue_size | int  | 1000    |
+------------------+------+---------+

``alert_queue_size`` is the maximum number of alerts queued up
internally. If alerts are not popped, the queue will eventually
fill up to this level.

.. _max_metadata_size:

.. raw:: html

	<a name="max_metadata_size"></a>

+-------------------+------+------------------+
| name              | type | default          |
+===================+======+==================+
| max_metadata_size | int  | 3 * 1024 * 10240 |
+-------------------+------+------------------+

``max_metadata_size`` is the maximum allowed size (in bytes) to be
received by the metadata extension, i.e. magnet links.

.. _hashing_threads:

.. raw:: html

	<a name="hashing_threads"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| hashing_threads | int  | 1       |
+-----------------+------+---------+

``hashing_threads`` is the number of threads to use for piece hash
verification. It defaults to 1. For very high download rates, on
machines with multiple cores, this could be incremented. Setting it
higher than the number of CPU cores would presumably not provide
any benefit of setting it to the number of cores. If it's set to 0,
hashing is done in the disk thread.

.. _checking_mem_usage:

.. raw:: html

	<a name="checking_mem_usage"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| checking_mem_usage | int  | 256     |
+--------------------+------+---------+

the number of blocks to keep outstanding at any given time when
checking torrents. Higher numbers give faster re-checks but uses
more memory. Specified in number of 16 kiB blocks

.. _predictive_piece_announce:

.. raw:: html

	<a name="predictive_piece_announce"></a>

+---------------------------+------+---------+
| name                      | type | default |
+===========================+======+=========+
| predictive_piece_announce | int  | 0       |
+---------------------------+------+---------+

if set to > 0, pieces will be announced to other peers before they
are fully downloaded (and before they are hash checked). The
intention is to gain 1.5 potential round trip times per downloaded
piece. When non-zero, this indicates how many milliseconds in
advance pieces should be announced, before they are expected to be
completed.

.. _aio_threads:

.. _aio_max:

.. raw:: html

	<a name="aio_threads"></a>
	<a name="aio_max"></a>

+-------------+------+---------+
| name        | type | default |
+=============+======+=========+
| aio_threads | int  | 4       |
+-------------+------+---------+
| aio_max     | int  | 300     |
+-------------+------+---------+

for some aio back-ends, ``aio_threads`` specifies the number of
io-threads to use,  and ``aio_max`` the max number of outstanding
jobs.

.. _network_threads:

.. raw:: html

	<a name="network_threads"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| network_threads | int  | 0       |
+-----------------+------+---------+

``network_threads`` is the number of threads to use to call
``async_write_some`` (i.e. send) on peer connection sockets. When
seeding at extremely high rates, this may become a bottleneck, and
setting this to 2 or more may parallelize that cost. When using SSL
torrents, all encryption for outgoing traffic is done withint the
socket send functions, and this will help parallelizing the cost of
SSL encryption as well.

.. _ssl_listen:

.. raw:: html

	<a name="ssl_listen"></a>

+------------+------+---------+
| name       | type | default |
+============+======+=========+
| ssl_listen | int  | 4433    |
+------------+------+---------+

``ssl_listen`` sets the listen port for SSL connections. If this is
set to 0, no SSL listen port is opened. Otherwise a socket is
opened on this port. This setting is only taken into account when
opening the regular listen port, and won't re-open the listen
socket simply by changing this setting.

.. _tracker_backoff:

.. raw:: html

	<a name="tracker_backoff"></a>

+-----------------+------+---------+
| name            | type | default |
+=================+======+=========+
| tracker_backoff | int  | 250     |
+-----------------+------+---------+

``tracker_backoff`` determines how aggressively to back off from
retrying failing trackers. This value determines *x* in the
following formula, determining the number of seconds to wait until
the next retry:

   delay = 5 + 5 * x / 100 * fails^2

This setting may be useful to make libtorrent more or less
aggressive in hitting trackers.

.. _share_ratio_limit:

.. _seed_time_ratio_limit:

.. raw:: html

	<a name="share_ratio_limit"></a>
	<a name="seed_time_ratio_limit"></a>

+-----------------------+------+---------+
| name                  | type | default |
+=======================+======+=========+
| share_ratio_limit     | int  | 200     |
+-----------------------+------+---------+
| seed_time_ratio_limit | int  | 700     |
+-----------------------+------+---------+

when a seeding torrent reaches eaither the share ratio (bytes up /
bytes down) or the seed time ratio (seconds as seed / seconds as
downloader) or the seed time limit (seconds as seed) it is
considered done, and it will leave room for other torrents these
are specified as percentages

.. _peer_turnover:

.. _peer_turnover_cutoff:

.. _peer_turnover_interval:

.. raw:: html

	<a name="peer_turnover"></a>
	<a name="peer_turnover_cutoff"></a>
	<a name="peer_turnover_interval"></a>

+------------------------+------+---------+
| name                   | type | default |
+========================+======+=========+
| peer_turnover          | int  | 4       |
+------------------------+------+---------+
| peer_turnover_cutoff   | int  | 90      |
+------------------------+------+---------+
| peer_turnover_interval | int  | 300     |
+------------------------+------+---------+

peer_turnover is the percentage of peers to disconnect every
turnover peer_turnover_interval (if we're at the peer limit), this
is specified in percent when we are connected to more than limit *
peer_turnover_cutoff peers disconnect peer_turnover fraction of the
peers. It is specified in percent peer_turnover_interval is the
interval (in seconds) between optimistic disconnects if the
disconnects happen and how many peers are disconnected is
controlled by peer_turnover and peer_turnover_cutoff

.. _connect_seed_every_n_download:

.. raw:: html

	<a name="connect_seed_every_n_download"></a>

+-------------------------------+------+---------+
| name                          | type | default |
+===============================+======+=========+
| connect_seed_every_n_download | int  | 10      |
+-------------------------------+------+---------+

this setting controls the priority of downloading torrents over
seeding or finished torrents when it comes to making peer
connections. Peer connections are throttled by the connection_speed
and the half-open connection limit. This makes peer connections a
limited resource. Torrents that still have pieces to download are
prioritized by default, to avoid having many seeding torrents use
most of the connection attempts and only give one peer every now
and then to the downloading torrent. libtorrent will loop over the
downloading torrents to connect a peer each, and every n:th
connection attempt, a finished torrent is picked to be allowed to
connect to a peer. This setting controls n.

.. _max_http_recv_buffer_size:

.. raw:: html

	<a name="max_http_recv_buffer_size"></a>

+---------------------------+------+------------+
| name                      | type | default    |
+===========================+======+============+
| max_http_recv_buffer_size | int  | 4*1024*204 |
+---------------------------+------+------------+

the max number of bytes to allow an HTTP response to be when
announcing to trackers or downloading .torrent files via the
``url`` provided in ``add_torrent_params``.

.. _max_retry_port_bind:

.. raw:: html

	<a name="max_retry_port_bind"></a>

+---------------------+------+---------+
| name                | type | default |
+=====================+======+=========+
| max_retry_port_bind | int  | 10      |
+---------------------+------+---------+

if binding to a specific port fails, should the port be incremented
by one and tried again? This setting specifies how many times to
retry a failed port bind

.. _alert_mask:

.. raw:: html

	<a name="alert_mask"></a>

+------------+------+---------------------------+
| name       | type | default                   |
+============+======+===========================+
| alert_mask | int  | alert::error_notification |
+------------+------+---------------------------+

a bitmask combining flags from alert::category_t defining which
kinds of alerts to receive

.. _out_enc_policy:

.. _in_enc_policy:

.. raw:: html

	<a name="out_enc_policy"></a>
	<a name="in_enc_policy"></a>

+----------------+------+---------------------------+
| name           | type | default                   |
+================+======+===========================+
| out_enc_policy | int  | settings_pack::pe_enabled |
+----------------+------+---------------------------+
| in_enc_policy  | int  | settings_pack::pe_enabled |
+----------------+------+---------------------------+

control the settings for incoming and outgoing connections
respectively. see enc_policy enum for the available options.
Keep in mind that protocol encryption degrades performance in
several respects:
1. It prevents "zero copy" disk buffers being sent to peers, since
   each peer needs to mutate the data (i.e. encrypt it) the data
   must be copied per peer connection rather than sending the same
   buffer to multiple peers.
2. The encryption itself requires more CPU than plain bittorrent
   protocol. The highest cost is the Diffie Hellman exchange on
   connection setup.
3. The encryption handshake adds several round-trips to the
connection setup, and delays transferring data.

.. _allowed_enc_level:

.. raw:: html

	<a name="allowed_enc_level"></a>

+-------------------+------+------------------------+
| name              | type | default                |
+===================+======+========================+
| allowed_enc_level | int  | settings_pack::pe_both |
+-------------------+------+------------------------+

determines the encryption level of the connections.  This setting
will adjust which encryption scheme is offered to the other peer,
as well as which encryption scheme is selected by the client. See
enc_level enum for options.

.. _inactive_down_rate:

.. _inactive_up_rate:

.. raw:: html

	<a name="inactive_down_rate"></a>
	<a name="inactive_up_rate"></a>

+--------------------+------+---------+
| name               | type | default |
+====================+======+=========+
| inactive_down_rate | int  | 2048    |
+--------------------+------+---------+
| inactive_up_rate   | int  | 2048    |
+--------------------+------+---------+

the download and upload rate limits for a torrent to be considered
active by the queuing mechanism. A torrent whose download rate is
less than ``inactive_down_rate`` and whose upload rate is less than
``inactive_up_rate`` for ``auto_manage_startup`` seconds, is
considered inactive, and another queued torrent may be startert.
This logic is disabled if ``dont_count_slow_torrents`` is false.

.. _proxy_type:

.. raw:: html

	<a name="proxy_type"></a>

+------------+------+---------------------+
| name       | type | default             |
+============+======+=====================+
| proxy_type | int  | settings_pack::none |
+------------+------+---------------------+

proxy to use, defaults to none. see proxy_type_t.

.. _proxy_port:

.. raw:: html

	<a name="proxy_port"></a>

+------------+------+---------+
| name       | type | default |
+============+======+=========+
| proxy_port | int  | 0       |
+------------+------+---------+

the port of the proxy server

.. _i2p_port:

.. raw:: html

	<a name="i2p_port"></a>

+----------+------+---------+
| name     | type | default |
+==========+======+=========+
| i2p_port | int  | 0       |
+----------+------+---------+

sets the i2p_ SAM bridge port to connect to. set the hostname with
the ``i2p_hostname`` setting.

.. _i2p: http://www.i2p2.de

