docs: add statement on our refusal to insert backdoors

[tahoe-lafs/tahoe-lafs.git] / docs / configuration.txt

= Configuring a Tahoe node =

A Tahoe node is configured by writing to files in its base directory. These
files are read by the node when it starts, so each time you change them, you
need to restart the node.

The node also writes state to its base directory, so it will create files on
its own.

This document contains a complete list of the config files that are examined
by the client node, as well as the state files that you'll observe in its
base directory.

The main file is named 'tahoe.cfg', which is an ".INI"-style configuration
file (parsed by the Python stdlib 'ConfigParser' module: "[name]" section
markers, lines with "key.subkey: value", rfc822-style continuations). There
are other files that contain information which does not easily fit into this
format. The 'tahoe create-node' or 'tahoe create-client' command will create
an initial tahoe.cfg file for you. After creation, the node will never modify
the 'tahoe.cfg' file: all persistent state is put in other files.

The item descriptions below use the following types:

 boolean: one of (True, yes, on, 1, False, off, no, 0), case-insensitive
 strports string: a Twisted listening-port specification string, like "tcp:80"
                  or "tcp:3456:interface=127.0.0.1". For a full description of
                  the format, see
                  http://twistedmatrix.com/documents/current/api/twisted.application.strports.html
 FURL string: a Foolscap endpoint identifier, like
              pb://soklj4y7eok5c3xkmjeqpw@192.168.69.247:44801/eqpwqtzm


== Overall Node Configuration ==

This section controls the network behavior of the node overall: which ports
and IP addresses are used, when connections are timed out, etc. This
configuration is independent of the services that the node is offering: the
same controls are used for client and introducer nodes.

If your node is behind a firewall or NAT device and you want other clients to
connect to it, you'll need to open a port in the firewall or NAT, and specify
that port number in the tub.port option. If behind a NAT, you *may* need to
set the tub.location option described below.


[node]

nickname = (UTF-8 string, optional)

 This value will be displayed in management tools as this node's "nickname".
 If not provided, the nickname will be set to "<unspecified>". This string
 shall be a UTF-8 encoded unicode string.

web.port = (strports string, optional)

 This controls where the node's webserver should listen, providing filesystem
 access and node status as defined in webapi.txt . This file contains a
 Twisted "strports" specification such as "3456" or
 "tcp:3456:interface=127.0.0.1". The 'tahoe create-node' or 'tahoe create-client'
 commands set the web.port to "tcp:3456:interface=127.0.0.1" by default; this
 is overridable by the "--webport" option. You can make it use SSL by writing
 "ssl:3456:privateKey=mykey.pem:certKey=cert.pem" instead.

 If this is not provided, the node will not run a web server.

web.static = (string, optional)

 This controls where the /static portion of the URL space is served. The
 value is a directory name (~username is allowed, and non-absolute names are
 interpreted relative to the node's basedir) which can contain HTML and other
 files. This can be used to serve a javascript-based frontend to the Tahoe
 node, or other services.

 The default value is "public_html", which will serve $BASEDIR/public_html .
 With the default settings, http://127.0.0.1:3456/static/foo.html will serve
 the contents of $BASEDIR/public_html/foo.html .

tub.port = (integer, optional)

 This controls which port the node uses to accept Foolscap connections from
 other nodes. If not provided, the node will ask the kernel for any available
 port. The port will be written to a separate file (named client.port or
 introducer.port), so that subsequent runs will re-use the same port.

tub.location = (string, optional)

 In addition to running as a client, each Tahoe node also runs as a server,
 listening for connections from other Tahoe clients. The node announces its
 location by publishing a "FURL" (a string with some connection hints) to the
 Introducer. The string it publishes can be found in
 $BASEDIR/private/storage.furl . The "tub.location" configuration controls
 what location is published in this announcement.

 If you don't provide tub.location, the node will try to figure out a useful
 one by itself, by using tools like 'ifconfig' to determine the set of IP
 addresses on which it can be reached from nodes both near and far. It will
 also include the TCP port number on which it is listening (either the one
 specified by tub.port, or whichever port was assigned by the kernel when
 tub.port is left unspecified).

 You might want to override this value if your node lives behind a firewall
 that is doing inbound port forwarding, or if you are using other proxies
 such that the local IP address or port number is not the same one that
 remote clients should use to connect. You might also want to control this
 when using a Tor proxy to avoid revealing your actual IP address through the
 Introducer announcement.

 The value is a comma-separated string of host:port location hints, like
 this:

  123.45.67.89:8098,tahoe.example.com:8098,127.0.0.1:8098

 A few examples:

  Emulate default behavior, assuming your host has IP address 123.45.67.89
  and the kernel-allocated port number was 8098:

   tub.port = 8098
   tub.location = 123.45.67.89:8098,127.0.0.1:8098

  Use a DNS name so you can change the IP address more easily:

   tub.port = 8098
   tub.location = tahoe.example.com:8098

  Run a node behind a firewall (which has an external IP address) that has
  been configured to forward port 7912 to our internal node's port 8098:

   tub.port = 8098
   tub.location = external-firewall.example.com:7912

  Run a node behind a Tor proxy (perhaps via torsocks), in client-only mode
  (i.e. we can make outbound connections, but other nodes will not be able to
  connect to us). The literal 'unreachable.example.org' will not resolve, but
  will serve as a reminder to human observers that this node cannot be
  reached. "Don't call us.. we'll call you":

   tub.port = 8098
   tub.location = unreachable.example.org:0

  Run a node behind a Tor proxy, and make the server available as a Tor
  "hidden service". (this assumes that other clients are running their node
  with torsocks, such that they are prepared to connect to a .onion address).
  The hidden service must first be configured in Tor, by giving it a local
  port number and then obtaining a .onion name, using something in the torrc
  file like:

    HiddenServiceDir /var/lib/tor/hidden_services/tahoe
    HiddenServicePort 29212 127.0.0.1:8098

   once Tor is restarted, the .onion hostname will be in
   /var/lib/tor/hidden_services/tahoe/hostname . Then set up your tahoe.cfg
   like:

    tub.port = 8098
    tub.location = ualhejtq2p7ohfbb.onion:29212

 Most users will not need to set tub.location .

 Note that the old 'advertised_ip_addresses' file from earlier releases is no
 longer supported. Tahoe 1.3.0 and later will ignore this file.

log_gatherer.furl = (FURL, optional)

 If provided, this contains a single FURL string which is used to contact a
 'log gatherer', which will be granted access to the logport. This can be
 used by centralized storage meshes to gather operational logs in a single
 place. Note that when an old-style BASEDIR/log_gatherer.furl file exists
 (see 'Backwards Compatibility Files', below), both are used. (for most other
 items, the separate config file overrides the entry in tahoe.cfg)

timeout.keepalive = (integer in seconds, optional)
timeout.disconnect = (integer in seconds, optional)

 If timeout.keepalive is provided, it is treated as an integral number of
 seconds, and sets the Foolscap "keepalive timer" to that value. For each
 connection to another node, if nothing has been heard for a while, we will
 attempt to provoke the other end into saying something. The duration of
 silence that passes before sending the PING will be between KT and 2*KT.
 This is mainly intended to keep NAT boxes from expiring idle TCP sessions,
 but also gives TCP's long-duration keepalive/disconnect timers some traffic
 to work with. The default value is 240 (i.e. 4 minutes).

 If timeout.disconnect is provided, this is treated as an integral number of
 seconds, and sets the Foolscap "disconnect timer" to that value. For each
 connection to another node, if nothing has been heard for a while, we will
 drop the connection. The duration of silence that passes before dropping the
 connection will be between DT-2*KT and 2*DT+2*KT (please see ticket #521 for
 more details). If we are sending a large amount of data to the other end
 (which takes more than DT-2*KT to deliver), we might incorrectly drop the
 connection. The default behavior (when this value is not provided) is to
 disable the disconnect timer.

 See ticket #521 for a discussion of how to pick these timeout values. Using
 30 minutes means we'll disconnect after 22 to 68 minutes of inactivity.
 Receiving data will reset this timeout, however if we have more than 22min
 of data in the outbound queue (such as 800kB in two pipelined segments of 10
 shares each) and the far end has no need to contact us, our ping might be
 delayed, so we may disconnect them by accident.

ssh.port = (strports string, optional)
ssh.authorized_keys_file = (filename, optional)

 This enables an SSH-based interactive Python shell, which can be used to
 inspect the internal state of the node, for debugging. To cause the node to
 accept SSH connections on port 8022 from the same keys as the rest of your
 account, use:

   [tub]
   ssh.port = 8022
   ssh.authorized_keys_file = ~/.ssh/authorized_keys

tempdir = (string, optional)

 This specifies a temporary directory for the webapi server to use, for
 holding large files while they are being uploaded. If a webapi client
 attempts to upload a 10GB file, this tempdir will need to have at least 10GB
 available for the upload to complete.

 The default value is the "tmp" directory in the node's base directory (i.e.
 $NODEDIR/tmp), but it can be placed elsewhere. This directory is used for
 files that usually (on a unix system) go into /tmp . The string will be
 interpreted relative to the node's base directory.

== Client Configuration ==

[client]
introducer.furl = (FURL string, mandatory)

 This FURL tells the client how to connect to the introducer. Each Tahoe grid
 is defined by an introducer. The introducer's furl is created by the
 introducer node and written into its base directory when it starts,
 whereupon it should be published to everyone who wishes to attach a client
 to that grid

helper.furl = (FURL string, optional)

 If provided, the node will attempt to connect to and use the given helper
 for uploads. See docs/helper.txt for details.

key_generator.furl = (FURL string, optional)

 If provided, the node will attempt to connect to and use the given
 key-generator service, using RSA keys from the external process rather than
 generating its own.

stats_gatherer.furl = (FURL string, optional)

 If provided, the node will connect to the given stats gatherer and provide
 it with operational statistics.

shares.needed = (int, optional) aka "k", default 3
shares.total = (int, optional) aka "N", N >= k, default 10
shares.happy = (int, optional) 1 <= happy <= N, default 7

 These three values set the default encoding parameters. Each time a new file
 is uploaded, erasure-coding is used to break the ciphertext into separate
 pieces. There will be "N" (i.e. shares.total) pieces created, and the file
 will be recoverable if any "k" (i.e. shares.needed) pieces are retrieved.
 The default values are 3-of-10 (i.e. shares.needed = 3, shares.total = 10).
 Setting k to 1 is equivalent to simple replication (uploading N copies of
 the file).

 These values control the tradeoff between storage overhead, performance, and
 reliability. To a first approximation, a 1MB file will use (1MB*N/k) of
 backend storage space (the actual value will be a bit more, because of other
 forms of overhead). Up to N-k shares can be lost before the file becomes
 unrecoverable, so assuming there are at least N servers, up to N-k servers
 can be offline without losing the file. So large N/k ratios are more
 reliable, and small N/k ratios use less disk space. Clearly, k must never be
 smaller than N.

 Large values of N will slow down upload operations slightly, since more
 servers must be involved, and will slightly increase storage overhead due to
 the hash trees that are created. Large values of k will cause downloads to
 be marginally slower, because more servers must be involved. N cannot be
 larger than 256, because of the 8-bit erasure-coding algorithm that Tahoe
 uses.

 shares.happy allows you control over the distribution of your immutable file.
 For a successful upload, shares are guaranteed to be initially placed on
 at least 'shares.happy' distinct servers, the correct functioning of any
 k of which is sufficient to guarantee the availability of the uploaded file.
 This value should not be larger than the number of servers on your grid.
 
 A value of shares.happy <= k is allowed, but does not provide any redundancy
 if some servers fail or lose shares.

 (Mutable files use a different share placement algorithm that does not 
  consider this parameter.)


== Storage Server Configuration ==

[storage]
enabled = (boolean, optional)

 If this is True, the node will run a storage server, offering space to other
 clients. If it is False, the node will not run a storage server, meaning
 that no shares will be stored on this node. Use False this for clients who
 do not wish to provide storage service. The default value is True.

readonly = (boolean, optional)

 If True, the node will run a storage server but will not accept any shares,
 making it effectively read-only. Use this for storage servers which are
 being decommissioned: the storage/ directory could be mounted read-only,
 while shares are moved to other servers. Note that this currently only
 affects immutable shares. Mutable shares (used for directories) will be
 written and modified anyway. See ticket #390 for the current status of this
 bug. The default value is False.

reserved_space = (str, optional)

 If provided, this value defines how much disk space is reserved: the storage
 server will not accept any share which causes the amount of free disk space
 to drop below this value. (The free space is measured by a call to statvfs(2)
 on Unix, or GetDiskFreeSpaceEx on Windows, and is the space available to the
 user account under which the storage server runs.)

 This string contains a number, with an optional case-insensitive scale
 suffix like "K" or "M" or "G", and an optional "B" or "iB" suffix. So
 "100MB", "100M", "100000000B", "100000000", and "100000kb" all mean the same
 thing. Likewise, "1MiB", "1024KiB", and "1048576B" all mean the same thing.

expire.enabled =
expire.mode =
expire.override_lease_duration =
expire.cutoff_date =
expire.immutable =
expire.mutable =

 These settings control garbage-collection, in which the server will delete
 shares that no longer have an up-to-date lease on them. Please see the
 neighboring "garbage-collection.txt" document for full details.


== Running A Helper ==

A "helper" is a regular client node that also offers the "upload helper"
service.

[helper]
enabled = (boolean, optional)

 If True, the node will run a helper (see docs/helper.txt for details). The
 helper's contact FURL will be placed in private/helper.furl, from which it
 can be copied to any clients which wish to use it. Clearly nodes should not
 both run a helper and attempt to use one: do not create both helper.furl and
 run_helper in the same node. The default is False.


== Running An Introducer ==

The introducer node uses a different '.tac' file (named introducer.tac), and
pays attention to the "[node]" section, but not the others.

The Introducer node maintains some different state than regular client
nodes.

BASEDIR/introducer.furl : This is generated the first time the introducer
node is started, and used again on subsequent runs, to give the introduction
service a persistent long-term identity. This file should be published and
copied into new client nodes before they are started for the first time.


== Other Files in BASEDIR ==

Some configuration is not kept in tahoe.cfg, for the following reasons:

 * it is generated by the node at startup, e.g. encryption keys. The node
   never writes to tahoe.cfg
 * it is generated by user action, e.g. the 'tahoe create-alias' command

In addition, non-configuration persistent state is kept in the node's base
directory, next to the configuration knobs.

This section describes these other files.


private/node.pem : This contains an SSL private-key certificate. The node
generates this the first time it is started, and re-uses it on subsequent
runs. This certificate allows the node to have a cryptographically-strong
identifier (the Foolscap "TubID"), and to establish secure connections to
other nodes.

storage/ : Nodes which host StorageServers will create this directory to hold
shares of files on behalf of other clients. There will be a directory
underneath it for each StorageIndex for which this node is holding shares.
There is also an "incoming" directory where partially-completed shares are
held while they are being received.

client.tac : this file defines the client, by constructing the actual Client
instance each time the node is started. It is used by the 'twistd'
daemonization program (in the "-y" mode), which is run internally by the
"tahoe start" command. This file is created by the "tahoe create-node" or
"tahoe create-client" commands.

private/control.furl : this file contains a FURL that provides access to a
control port on the client node, from which files can be uploaded and
downloaded. This file is created with permissions that prevent anyone else
from reading it (on operating systems that support such a concept), to insure
that only the owner of the client node can use this feature. This port is
intended for debugging and testing use.

private/logport.furl : this file contains a FURL that provides access to a
'log port' on the client node, from which operational logs can be retrieved.
Do not grant logport access to strangers, because occasionally secret
information may be placed in the logs.

private/helper.furl : if the node is running a helper (for use by other
clients), its contact FURL will be placed here. See docs/helper.txt for more
details.

private/root_dir.cap (optional): The command-line tools will read a directory
cap out of this file and use it, if you don't specify a '--dir-cap' option or
if you specify '--dir-cap=root'.

private/convergence (automatically generated): An added secret for encrypting
immutable files. Everyone who has this same string in their
private/convergence file encrypts their immutable files in the same way when
uploading them. This causes identical files to "converge" -- to share the
same storage space since they have identical ciphertext -- which conserves
space and optimizes upload time, but it also exposes files to the possibility
of a brute-force attack by people who know that string. In this attack, if
the attacker can guess most of the contents of a file, then they can use
brute-force to learn the remaining contents.

So the set of people who know your private/convergence string is the set of
people who converge their storage space with you when you and they upload
identical immutable files, and it is also the set of people who could mount
such an attack.

The content of the private/convergence file is a base-32 encoded string. If
the file doesn't exist, then when the Tahoe client starts up it will generate
a random 256-bit string and write the base-32 encoding of this string into
the file. If you want to converge your immutable files with as many people as
possible, put the empty string (so that private/convergence is a zero-length
file).


== Other files ==

logs/ : Each Tahoe node creates a directory to hold the log messages produced
as the node runs. These logfiles are created and rotated by the "twistd"
daemonization program, so logs/twistd.log will contain the most recent
messages, logs/twistd.log.1 will contain the previous ones, logs/twistd.log.2
will be older still, and so on. twistd rotates logfiles after they grow
beyond 1MB in size. If the space consumed by logfiles becomes troublesome,
they should be pruned: a cron job to delete all files that were created more
than a month ago in this logs/ directory should be sufficient.

my_nodeid : this is written by all nodes after startup, and contains a
base32-encoded (i.e. human-readable) NodeID that identifies this specific
node. This NodeID is the same string that gets displayed on the web page (in
the "which peers am I connected to" list), and the shortened form (the first
characters) is recorded in various log messages.


== Backwards Compatibility Files ==

Tahoe releases before 1.3.0 had no 'tahoe.cfg' file, and used distinct files
for each item listed below. For each configuration knob, if the distinct file
exists, it will take precedence over the corresponding item in tahoe.cfg .


[node]nickname : BASEDIR/nickname
[node]web.port : BASEDIR/webport
[node]tub.port : BASEDIR/client.port  (for Clients, not Introducers)
[node]tub.port : BASEDIR/introducer.port  (for Introducers, not Clients)
      (note that, unlike other keys, tahoe.cfg overrides the *.port file)
[node]tub.location : replaces BASEDIR/advertised_ip_addresses
[node]log_gatherer.furl : BASEDIR/log_gatherer.furl (one per line)
[node]timeout.keepalive : BASEDIR/keepalive_timeout
[node]timeout.disconnect : BASEDIR/disconnect_timeout
[client]introducer.furl : BASEDIR/introducer.furl
[client]helper.furl : BASEDIR/helper.furl
[client]key_generator.furl : BASEDIR/key_generator.furl
[client]stats_gatherer.furl : BASEDIR/stats_gatherer.furl
[storage]enabled : BASEDIR/no_storage (False if no_storage exists)
[storage]readonly : BASEDIR/readonly_storage (True if readonly_storage exists)
[storage]sizelimit : BASEDIR/sizelimit
[storage]debug_discard : BASEDIR/debug_discard_storage
[helper]enabled : BASEDIR/run_helper (True if run_helper exists)

Note: the functionality of [node]ssh.port and [node]ssh.authorized_keys_file
were previously combined, controlled by the presence of a
BASEDIR/authorized_keys.SSHPORT file, in which the suffix of the filename
indicated which port the ssh server should listen on, and the contents of the
file provided the ssh public keys to accept. Support for these files has been
removed completely. To ssh into your Tahoe node, add [node]ssh.port and
[node].ssh_authorized_keys_file statements to your tahoe.cfg .

Likewise, the functionality of [node]tub.location is a variant of the
now-unsupported BASEDIR/advertised_ip_addresses . The old file was additive
(the addresses specified in advertised_ip_addresses were used in addition to
any that were automatically discovered), whereas the new tahoe.cfg directive
is not (tub.location is used verbatim).


== Example ==

The following is a sample tahoe.cfg file, containing values for all keys
described above. Note that this is not a recommended configuration (most of
these are not the default values), merely a legal one.

[node]
nickname = Bob's Tahoe Node
tub.port = 34912
tub.location = 123.45.67.89:8098,44.55.66.77:8098
web.port = 3456
log_gatherer.furl = pb://soklj4y7eok5c3xkmjeqpw@192.168.69.247:44801/eqpwqtzm
timeout.keepalive = 240
timeout.disconnect = 1800
ssh.port = 8022
ssh.authorized_keys_file = ~/.ssh/authorized_keys

[client]
introducer.furl = pb://ok45ssoklj4y7eok5c3xkmj@tahoe.example:44801/ii3uumo
helper.furl = pb://ggti5ssoklj4y7eok5c3xkmj@helper.tahoe.example:7054/kk8lhr

[storage]
enabled = True
readonly_storage = True
sizelimit = 10000000000

[helper]
run_helper = True