tor - The second-generation onion router

tor [OPTION value]...

tor is a connection-oriented anonymizing communication service. Users choose a source-routed path through a set of nodes, and negotiate a "virtual circuit" through the network, in which each node knows its predecessor and successor, but no others. Traffic flowing down the circuit is unwrapped by a symmetric key at each node, which reveals the downstream node.

Basically tor provides a distributed network of servers ("onion routers"). Users bounce their TCP streams -- web traffic, ftp, ssh, etc -- around the routers, and recipients, observers, and even the routers themselves have difficulty tracking the source of the stream.

-h, -help Display a short help message and exit.

-f FILE

FILE contains further "option value" pairs. (Default: /etc/tor/torrc)

Other options can be specified either on the command-line (--option value), or in the configuration file (option value). Options are case-insensitive.

BandwidthRate N bytes|KB|MB|GB|TB

A token bucket limits the average incoming bandwidth on this node to the specified number of bytes per second. (Default: 2 MB)

BandwidthBurst N bytes|KB|MB|GB|TB

Limit the maximum token bucket size (also known as the burst) to the given number of bytes. (Default: 5 MB)

MaxAdvertisedBandwidth N bytes|KB|MB|GB|TB

If set, we will not advertise more than this amount of bandwidth for our BandwidthRate. Server operators who want to reduce the number of clients who ask to build circuits through them (since this is proportional to advertised bandwidth rate) can thus reduce the CPU demands on their server without impacting network performance.

ControlPort Port

If set, Tor will accept connections from the same machine (localhost only) on this port, and allow those connections to control the Tor process using the Tor Control Protocol (described in control-spec.txt). Note: unless you also specify one of HashedControlPassword or CookieAuthentication, setting this option will cause Tor to allow any process on the local host to control it.

HashedControlPassword hashed_password

Don't allow any connections on the control port except when the other process knows the password whose one-way hash is hashed_password. You can compute the hash of a password by running "tor --hash-password password".

CookieAuthentication 0|1

If this option is set to 1, don't allow any connections on the control port except when the connecting process knows the contents of a file named "control_auth_cookie", which Tor will create in its data directory. This authentication methods should only be used on systems with good filesystem security. (Default: 0)

DataDirectory DIR

Store working data in DIR (Default: /var/lib/tor)

DirFetchPeriod N seconds|minutes|hours|days|weeks

Every time the specified period elapses, Tor downloads a directory. A directory contains a signed list of all known servers as well as their current liveness status. A value of "0 seconds" tells Tor to choose an appropriate default. (Default: 1 hour for clients, 20 minutes for servers)

DirServer address:port fingerprint

Use a nonstandard authoritative directory server at the provided address and port, with the specified key fingerprint. This option can be repeated many times, for multiple authoritative directory servers. If no dirserver line is given, Tor will use the default directory servers: moria1, moria2, and tor26.

Group GID

On startup, setgid to this user.

HttpProxy host[:port]

Tor will make all its directory requests through this host:port (or host:80 if port is not specified), rather than connecting directly to any directory servers.

HttpProxyAuthenticator username:password

If defined, Tor will use this username:password for Basic Http proxy authentication, as in RFC 2617. This is currently the only form of Http proxy authentication that Tor supports; feel free to submit a patch if you want it to support others.

HttpsProxy host[:port]

Tor will make all its OR (SSL) connections through this host:port (or host:443 if port is not specified), via HTTP CONNECT rather than connecting directly to servers. You may want to set FascistFirewall to restrict the set of ports you might try to connect to, if your Https proxy only allows connecting to certain ports.

HttpsProxyAuthenticator username:password

If defined, Tor will use this username:password for Basic Https proxy authentication, as in RFC 2617. This is currently the only form of Https proxy authentication that Tor supports; feel free to submit a patch if you want it to support others.

KeepalivePeriod NUM

To keep firewalls from expiring connections, send a padding keepalive cell every NUM seconds on open connections that are in use. If the connection has no open circuits, it will instead be closed after NUM seconds of idleness. (Default: 5 minutes)

Log minSeverity[-maxSeverity] stderr|stdout|syslog

Send all messages between minSeverity and maxSeverity to the standard output stream, the standard error stream, or to the system log. (The "syslog" value is only supported on Unix.) Recognized severity levels are debug, info, notice, warn, and err. If only one severity level is given, all messages of that level or higher will be sent to the listed destination.

Log minSeverity[-maxSeverity] file FILENAME

As above, but send log messages to the listed filename. The "Log" option may appear more than once in a configuration file. Messages are sent to all the logs that match their severity level.

MaxConn NUM

Maximum number of simultaneous sockets allowed. You probably don't need to adjust this. (Default: 1024)

OutboundBindAddress IP

Make all outbound connections originate from the IP address specified. This is only useful when you have multiple network interfaces, and you want all of Tor's outgoing connections to use a single one.

PIDFile FILE

On startup, write our PID to FILE. On clean shutdown, remove FILE.

RunAsDaemon 0|1

If 1, Tor forks and daemonizes to the background. (Default: 0)

SafeLogging 0|1

If 1, Tor replaces potentially sensitive strings in the logs (e.g. addresses) with the string [scrubbed]. This way logs can still be useful, but they don't leave behind personally identifying information about what sites a user might have visited. (Default: 1)

StatusFetchPeriod N seconds|minutes|hours|days|weeks

Every time the specified period elapses, Tor downloads signed status information about the current state of known servers. A value of "0 seconds" tells Tor to choose an appropriate default. (Default: 30 minutes for clients, 15 minutes for servers)

User UID

On startup, setuid to this user.

The following options are useful only for clients (that is, if SOCKSPort is non-zero):

AllowUnverifiedNodes entry|exit|middle|introduction|rendezvous|...

Where on our circuits should we allow Tor servers that the directory servers haven't authenticated as "verified"? (Default: middle,rendezvous)

ClientOnly 0|1

If set to 1, Tor will under no circumstances run as a server. The default is to run as a client unless ORPort is configured. (Usually, you don't need to set this; Tor is pretty smart at figuring out whether you are reliable and high-bandwidth enough to be a useful server.)

This option will likely be deprecated in the future; see the NoPublish option below. (Default: 0)

EntryNodes nickname,nickname,...

A list of preferred nodes to use for the first hop in the circuit, if possible.

ExitNodes nickname,nickname,...

A list of preferred nodes to use for the last hop in the circuit, if possible.

ExcludeNodes nickname,nickname,...

A list of nodes to never use when building a circuit.

StrictExitNodes 0|1

If 1, Tor will never use any nodes besides those listed in "exitnodes" for the last hop of a circuit.

StrictEntryNodes 0|1

If 1, Tor will never use any nodes besides those listed in "entrynodes" for the first hop of a circuit.

FascistFirewall 0|1

If 1, Tor will only create outgoing connections to ORs running on ports that your firewall allows (defaults to 80 and 443; see FirewallPorts). This will allow you to run Tor as a client behind a firewall with restrictive policies, but will not allow you to run as a server behind such a firewall.

FirewallPorts PORTS

A list of ports that your firewall allows you to connect to. Only used when FascistFirewall is set. (Default: 80, 443)

LongLivedPorts PORTS

A list of ports for services that tend to have long-running connections (e.g. chat and interactive shells). Circuits for streams that use these ports will contain only high-uptime nodes, to reduce the chance that a node will go down before the stream is finished. (Default: 21, 22, 706, 1863, 5050, 5190, 5222, 5223, 6667, 8300, 8888)

MapAddress address newaddress

When a request for address arrives to Tor, it will rewrite it to newaddress before processing it. For example, if you always want connections to www.indymedia.org to exit via torserver (where torserver is the nickname of the server), use "MapAddress www.indymedia.org www.indymedia.org.torserver.exit".

NewCircuitPeriod NUM

Every NUM seconds consider whether to build a new circuit. (Default: 30 seconds)

MaxCircuitDirtiness NUM

Feel free to reuse a circuit that was first used at most NUM seconds ago, but never attach a new stream to a circuit that is too old. (Default: 10 minutes)

NodeFamily nickname,nickname,...

The named Tor servers constitute a "family" of similar or co-administered servers, so never use any two of them in the same circuit. Defining a NodeFamily is only needed when a server doesn't list the family itself (with MyFamily). This option can be used multiple times.

RendNodes nickname,nickname,... A list of preferred nodes to use for the rendezvous point, if possible.

RendExcludeNodes nickname,nickname,...

A list of nodes to never use when choosing a rendezvous point.

SOCKSPort PORT

Advertise this port to listen for connections from SOCKS-speaking applications. Set this to 0 if you don't want to allow application connections. (Default: 9050)

SOCKSBindAddress IP[:PORT]

Bind to this address to listen for connections from SOCKS-speaking applications. (Default: 127.0.0.1) You can also specify a port (e.g. 192.168.0.1:9100). This directive can be specified multiple times to bind to multiple addresses/ports.

SOCKSPolicy policy,policy,...

Set an entrance policy for this server, to limit who can connect to the SOCKS ports. The policies have the same form as exit policies below.

TrackHostExits host,.domain,...

For each value in the comma separated list, Tor will track recent connections to hosts that match this value and attempt to reuse the same exit node for each. If the value is prepended with a '.', it is treated as matching an entire domain. If one of the values is just a '.', it means match everything. This option is useful if you frequently connect to sites that will expire all your authentication cookies (ie log you out) if your IP address changes. Note that this option does have the disadvantage of making it more clear that a given history is associated with a single user. However, most people who would wish to observe this will observe it through cookies or other protocol-specific means anyhow.

TrackHostExitsExpire NUM

Since exit servers go up and down, it is desirable to expire the association between host and exit server after NUM seconds of inactivity. The default is 1800 seconds (30 minutes).

The following options are useful only for servers (that is, if ORPort is non-zero):

Address address

The IP or fqdn of this server (e.g. moria.mit.edu). You can leave this unset, and Tor will guess your IP.

ContactInfo email_address

Administrative contact information for server.

ExitPolicy policy,policy,...

Set an exit policy for this server. Each policy is of the form "accept|reject ADDR[/MASK][:PORT]". If /MASK is omitted then this policy just applies to the host given. Instead of giving a host or network you can also use "*" to denote the universe (0.0.0.0/0). PORT can be a single port number, an interval of ports "FROM_PORT-TO_PORT", or "*". If PORT is omitted, that means "*".

For example, "reject 127.0.0.1:*,reject 192.168.1.0/24:*,accept *:*" would reject any traffic destined for localhost and any 192.168.1.* address, but accept anything else.

This directive can be specified multiple times so you don't have to put it all on one line.

See RFC 3330 for more details about internal and reserved IP address space. Policies are considered first to last, and the first match wins. If you want to _replace_ the default exit policy, end your exit policy with either a reject *:* or an accept *:*. Otherwise, you're _augmenting_ (prepending to) the default exit policy. The default exit policy is:

reject 0.0.0.0/8

reject 169.254.0.0/16

reject 127.0.0.0/8

reject 192.168.0.0/16

reject 10.0.0.0/8

reject 172.16.0.0/12

reject *:25

reject *:119

reject *:135-139

reject *:445

reject *:465

reject *:587

reject *:1214

reject *:4661-4666

reject *:6346-6429

reject *:6699

reject *:6881-6999

accept *:*

MaxOnionsPending NUM

If you have more than this number of onionskins queued for decrypt, reject new ones. (Default: 100)

MyFamily nickname,nickname,...

Declare that this Tor server is controlled or administered by a group or organization identical or similar to that of the other named servers. When two servers both declare that they are in the same 'family', Tor clients will not use them in the same circuit. (Each server only needs to list the other servers in its family; it doesn't need to list itself, but it won't hurt.)

Nickname name

Set the server's nickname to 'name'.

NoPublish 0|1

If you set NoPublish 1, Tor will act as a server if you have an ORPort defined, but it will not publish its descriptor to the dirservers. This option is useful if you're testing out your server, or if you're using alternate dirservers (e.g. for other Tor networks such as Blossom). (Default: 0)

NumCPUs num

How many processes to use at once for decrypting onionskins. (Default: 1)

ORPort PORT

Advertise this port to listen for connections from Tor clients and servers.

ORBindAddress IP[:PORT]

Bind to this IP address to listen for connections from Tor clients and servers. If you specify a port, bind to this port rather than the one specified in ORPort. (Default: 0.0.0.0)

RedirectExit pattern target

Whenever an outgoing connection tries to connect to one of a given set of addresses, connect to target (an address:port pair) instead. The address pattern is given in the same format as for an exit policy. The address translation applies after exit policies are applied. Multiple RedirectExit options can be used: once any one has matched successfully, no subsequent rules are considered. You can specify that no redirection is to be performed on a given set of addresses by using the special target string "pass", which prevents subsequent rules from being considered.

ShutdownWaitLength NUM

When we get a SIGINT and we're a server, we begin shutting down: we close listeners and start refusing new circuits. After NUM seconds, we exit. If we get a second SIGINT, we exit immediately. (Default: 30 seconds)

DirPostPeriod N seconds|minutes|hours|days|weeks

Every time the specified period elapses, Tor uploads its server descriptors to the directory servers. This information is also uploaded whenever it changes. (Default: 20 minutes)

AccountingMax N bytes|KB|MB|GB|TB

Never send more than the specified number of bytes in a given accounting period, or receive more than that number in the period. For example, with AccountingMax set to 1 GB, a server could send 900 MB and receive 800 MB and continue running. It will only hibernate once one of the two reaches 1 GB. When the number of bytes is exhausted, Tor will hibernate until some time in the next accounting period. To prevent all servers from waking at the same time, Tor will also wait until a random point in each period before waking up. If you have bandwidth cost issues, enabling hibernation is preferable to setting a low bandwidth, since it provides users with a collection of fast servers that are up some of the time, which is more useful than a set of slow servers that are always "available".

AccountingStart day|week|month [day] HH:MM

Specify how long accounting periods last. If month is given, each accounting period runs from the time HH:MM on the dayth day of one month to the same day and time of the next. (The day must be between 1 and 28.) If week is given, each accounting period runs from the time HH:MM of the dayth day of one week to the same day and time of the next week, with Monday as day 1 and Sunday as day 7. If day is given, each accounting period runs from the time HH:MM each day to the same time on the next day. All times are local, and given in 24-hour time. (Defaults to "month 1 0:00".)

The following options are useful only for directory servers (that is, if DirPort is non-zero):

AuthoritativeDirectory 0|1

When this option is set to 1, Tor operates as an authoritative directory server. Instead of caching the directory, it generates its own list of good servers, signs it, and sends that to the clients. Unless the clients already have you listed as a trusted directory, you probably do not want to set this option. Please coordinate with the other admins at tor-ops@freehaven.net if you think you should be a directory.

DirPort PORT

Advertise the directory service on this port.

DirBindAddress IP[:PORT]

Bind the directory service to this address. If you specify a port, bind to this port rather than the one specified in DirPort. (Default: 0.0.0.0)

DirPolicy policy,policy,...

Set an entrance policy for this server, to limit who can connect to the directory ports. The policies have the same form as exit policies above.

RecommendedVersions STRING

STRING is a command-separated list of Tor versions currently believed to be safe. The list is included in each directory, and nodes which pull down the directory learn whether they need to upgrade. This option can appear multiple times: the values from multiple lines are spliced together.

DirAllowPrivateAddresses 0|1

If set to 1, Tor will accept router descriptors with arbitrary "Address" elements. Otherwise, if the address is not an IP or is a private IP, it will reject the router descriptor. Defaults to 0.

RunTesting 0|1

If set to 1, Tor tries to build circuits through all of the servers it knows about, so it can tell which are up and which are down. This option is only useful for authoritative directories, so you probably don't want to use it.

The following options are used to configure a hidden service.

HiddenServiceDir DIRECTORY

Store data files for a hidden service in DIRECTORY. Every hidden service must have a separate directory. You may use this option multiple times to specify multiple services.

HiddenServicePort VIRTPORT [TARGET]

Configure a virtual port VIRTPORT for a hidden service. You may use this option multiple times; each time applies to the service using the most recent hiddenservicedir. By default, this option maps the virtual port to the same port on 127.0.0.1. You may override the target port, address, or both by specifying a target of addr, port, or addr:port.

HiddenServiceNodes nickname,nickname,...

If possible, use the specified nodes as introduction points for the hidden service. If this is left unset, Tor will be smart and pick some reasonable ones; most people can leave this unset.

HiddenServiceExcludeNodes nickname,nickname,...

Do not use the specified nodes as introduction points for the hidden service. In normal use there is no reason to set this.

RendPostPeriod N seconds|minutes|hours|days|weeks

Every time the specified period elapses, Tor uploads any rendezvous service descriptors to the directory servers. This information is also uploaded whenever it changes. (Default: 20 minutes)

Tor catches the following signals:

SIGTERM

Tor will catch this, clean up and sync to disk if necessary, and exit.

SIGINT

Tor clients behave as with SIGTERM; but Tor servers will do a controlled slow shutdown, closing listeners and waiting 30 seconds before exiting. (The delay can be configured with the ShutdownWaitLength config option.)

SIGHUP

The signal instructs Tor to reload its configuration (including closing and reopening logs), fetch a new directory, and kill and restart its helper processes if applicable.

SIGUSR1

Log statistics about current connections, past connections, and throughput.

SIGUSR2

Switch all logs to loglevel debug. You can go back to the old loglevels by sending a SIGHUP.

SIGCHLD

Tor receives this signal when one of its helper processes has exited, so it can clean up.

SIGPIPE

Tor catches this signal and ignores it.

SIGXFSZ

If this signal exists on your platform, Tor catches and ignores it.

/etc/tor/torrc

The configuration file, which contains "option value" pairs.

/var/lib/tor/

The tor process stores keys and other data here.

/var/log/tor/

The tor server logs to this directory.

/var/run/tor/tor.pid

The PID of the tor (master) process is stored in this file.

privoxy(1), tsocks(1), torify(1)

http://tor.eff.org/

Plenty, probably. Tor is still in development. Please report them.

Roger Dingledine <arma@mit.edu>, Nick Mathewson <nickm@alum.mit.edu>.