tahoe-lafs/docs/configuration.rst

========================
Configuring a Tahoe node
========================

1.  `Overall Node Configuration`_
2.  `Client Configuration`_
3.  `Storage Server Configuration`_
4.  `Running A Helper`_
5.  `Running An Introducer`_
6.  `Other Files in BASEDIR`_
7.  `Other files`_
8.  `Backwards Compatibility Files`_
9.  `Example`_

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.rst" 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.

===========================  ===============================  =================
Config setting               File                             Comment
===========================  ===============================  =================
[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 this file)
[node]tub.location           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