Configuring Serval DNA ====================== [Serval Project][], April 2013 Configuration options --------------------- The **servald** configuration is an unordered set of LABEL=VALUE pairs called *options*. For example: debug.verbose=true interfaces.0.file=/var/tmp/serval/dummy interfaces.0.socket_type=file log.file.directory_path=/var/tmp/serval-logs log.file.duration=20m log.file.rotate=10 rhizome.direct.peer.0.host=129.96.12.91 server.respawn_on_crash=true An option **LABEL** is a sequence of one or more [US-ASCII][] alphanumeric words separated by period characters, eg, `log.file.directory_path`. If a LABEL is not recognised, it is *unsupported*. An option **VALUE** is a string of [US-ASCII][] characters, excluding newline (character 10), which is parsed according to the option's *type*: * decimal integer, eg: `10`, `0`, `-1000000` * boolean, eg: `true`, `false`, `on`, `off`, `1`, `0`, `yes`, `no` * internet address (in\_addr), eg: `192.168.1.1` * time interval, eg: `12h`, `1w3d`, `2h15m30s` * absolute path, eg: `/var/lib/serval` * relative path, eg: `../lib/hostlist` * Serval ID (SID), eg: `EEBF3AC19E7EE58722A0F6D4A4D5894A72F5C71030C3399FE75808DCF6C6254B` * scaled decimal integer with optional suffix **k** (10^3), **K** (2^10), **m** (10^6), **M** (2^20), **g** (10^9) or **G** (2^30), eg: `1M` = 1,048,576 If a VALUE does not parse correctly, it is *invalid*. Instance directory ------------------ By default, **servald** stores its configuration, keyring, and other temporary files in its *instance directory*. The instance directory is set at run time by the `SERVALINSTANCE_PATH` environment variable. If this is not set, then **servald** uses a built-in default path which depends on its build-time option and target platform: * as specified by the `./configure INSTANCE_PATH=` option when **servald** was built from source * on Android `/data/data/org.servalproject/var/serval-node` * on other platforms `/var/serval-node` **servald** will create its instance directory (and all enclosing parent directories) if it does not already exist. Configuration persistence ------------------------- **servald** stores its configuration option settings in a file called `serval.conf` in its instance directory. It reads this file upon every invocation. This means that each instance's option settings persist until changed or until its `serval.conf` file is altered or removed. The format of the file is as shown in the example above: each option is represented by a single line in the file. Each line may have one of the forms: [ WHITE ] LABEL "=" VALUE "\n" [ WHITE ] "#" COMMENT "\n" [ WHITE ] "\n" where WHITE is any sequence of zero or more space or tab characters (as classified by [isspace(3)][]), COMMENT is any sequence of characters except newline, and LABEL and VALUE are as defined above. Blank lines are ignored, as are lines beginning with the comment character `#`. VALUE is parsed very strictly: all spaces are significant. A leading or trailing space in VALUE can cause a numerical option to be invalid. Invalid configuration --------------------- Although `serval.conf` is usually written and read only by **servald**, in fact it is an external file which may be modified, so **servald** has no control over its contents. The semantics of the configuration loading anticipate the possibility of encountering a *defective* file: * If `serval.conf` is syntactically malformed, then **servald** will log a warning, skip the malformed line and continue parsing; * If the same LABEL appears more than once, then **servald** will log a warning and ignore the second and all subsequent lines with the *duplicate* LABEL; * If an *unsupported* LABEL is encountered (which could be a mis-spelling of a supported option), then **servald** will log a warning and ignore the line; * If a configuration option has an *invalid* VALUE, then **servald** will log a warning and leave the option with its built-in default value; * If a logical relation, such as mutually incompatible or mandatory options, is violated, then **servald** will log a warning and ignore the *illogical* options or use default values. In all the above cases, most **servald** commands will reject the defective file by logging an error and exiting with error status (255). In this case, logging is done using options salvaged from the defective file (see the [config dump](#config-dump) command, described below). Some “permissive” commands, such as `help`, `stop`, and the various `config` commands described below, will not fail on a defective configuration file. Instead they will log a warning and carry on using options salvaged from the defective file. This means that **servald** may always be used to inspect and correct the configuration, and to stop a running daemon, despite a defective configuration file. Daemon processes ---------------- To run more than one **servald** daemon process on the same device, each daemon must have its own instance path (and hence its own `serval.conf`). Set the `SERVALINSTANCE_PATH` environment variable to a different directory path before starting each daemon. As described above, a defective `serval.conf` will prevent the **servald** `start` command from starting a daemon process. Once the daemon is running, it periodically checks whether `serval.conf` has changed (by comparing size and modification time) and attempts to re-load it if it detects a change. If the re-loaded file is defective, the daemon rejects it, logs an error, and continues execution with its prior configuration unchanged. If the daemon is stopped or killed, it cannot be re-started while `serval.conf` remains defective. About the examples ------------------ The examples in this document are [Bourne shell][] commands, using standard quoting and variable expansion. Commands issued by the user are prefixed with the shell prompt `$` to distinguish them from the output of the command. Single and double quotes around arguments are part of the shell syntax, so are not seen by the command. Lines ending in backslash `\` continue the command on the next line. Configuration commands ---------------------- ### config set To set a configuration option: $ servald config set name.of.option 'value' $ ### config del To unset (remove) a configuration option, returning it to its default value: $ servald config del name.of.option $ ### config set del Several **set** and **del** commands can be chained together in a single command: $ servald config set debug.verbose 1 \ del debug.dnahelper \ set log.file.path /tmp/log.txt $ ### config get To examine a single option's current value as defined in the `serval.conf` file (invalid, unsupported and illogical options may be examined, but not duplicate options): $ servald config get name.of.option name.of.option=value $ To examine all option settings defined in the `serval.conf` file, including invalid, unsupported and illogical options, but not duplicate options: $ servald config get interfaces=+eth0,+wifi0 name.of.option=value name.of.other_option=value2 $ ### config schema To list the names and types of all supported configuration options (the “configuration schema”): $ servald config schema debug.broadcasts=(boolean) debug.dnahelper=(boolean) debug.dnaresponses=(boolean) ... server.chdir=(absolute_path) server.interface_path=(str_nonempty) server.respawn_on_crash=(boolean) $ The configuration schema, with its default values, is defined in the [conf_schema.h](../conf_schema.h) source header file. ### config dump To examine all current *valid* configuration option settings, as produced by parsing `serval.conf` and omitting invalid, unsupported, duplicate and illogical options (ie, the configuration used by permissive commands and for logging): $ servald config dump --full debug.broadcasts=false debug.dnahelper=false debug.dnaresponses=false ... rhizome.rhizome_mdp_block_size=512 server.chdir=/ server.respawn_on_crash=true $ Omitting the `--full` argument omits all options which have their default value, leaving only the minimal settings that need be present in `serval.conf` to produce the current configuration: $ servald config dump debug.rhizome=true interfaces.0.file=/var/serval-node/dummy interfaces.0.socket_type=file rhizome.direct.peer.0.host=129.128.127.126 server.respawn_on_crash=true $ Logging configuration --------------------- **servald** logging is controlled by the following config options: log.console.level=debug|info|hint|warn|error|none log.console.dump_config=BOOLEAN log.console.show_pid=BOOLEAN log.console.show_time=BOOLEAN log.android.level=debug|info|hint|warn|error|none log.android.dump_config=BOOLEAN log.android.show_pid=BOOLEAN log.android.show_time=BOOLEAN log.file.level=debug|info|hint|warn|error|none log.file.dump_config=BOOLEAN log.file.show_pid=BOOLEAN log.file.show_time=BOOLEAN log.file.path=PATH log.file.directory_path=PATH log.file.duration=INTERVAL log.file.rotate=UINT There are three log output destinations, each of which can be configured independently of the others: * The *console* log destination is the standard error of the **servald** process, which is available in all command invocations of **servald**, but not in the background daemon process (the daemon closes all its standard IO streams when started in background mode). * The *android* log destination is available in **servald** executables built for the Android platform, and sends to the Android Log buffer that is accessible via the `adb logcat` command. On non-Android platforms, the `log.android` configuration options are supported but have no effect. * The *file* log destination is a log file created and appended directly by the **servald** process using the O\_APPEND option of [open(2)][] and a single [write(2)][] system call per log line (so concurrent **servald** processes will not corrupt each others' log lines). If the file does not exist, **servald** will create it and all its enclosing directories as needed. All log destinations support the following configuration options: * `log.DESTINATION.level` Log messages below this level are not sent to the destination. The lowest level is `debug`, and the highest is `error`. Setting this option to `none` suppresses all log messages. * `log.DESTINATION.dump_config` If true, then the current configuration is written to the destination (in `servald config dump` format), prior to other messages. * `log.DESTINATION.show_pid` If true, then every line written to this destination is prefixed with the Process ID of the process that produced it. * `log.DESTINATION.show_time` If true, then every line written to this destination is prefixed with the system time in millisecond resolution (if available) in the format `HH:MM:SS.mmm`. In addition, the *file* destination has these extra configuration options: * `log.file.directory_path` If set, log files are created in this directory, which is created if it does not exist. This defaults to the `log` directory within the instance directory. * `log.file.path` If set, all log messages are appended directly to the file at the given path. If the path is not absolute, it is interpreted relative the `log.file.directory_path` option. If `log.file.path` is not set, then log files have names of the form `serval-YYYYMMDDHHMMSS.log`, using the date/time of creation of the file. * `log.file.duration` If non zero, then a new log file is created every new interval. Interval boundaries are measured from the Unix epoch, so if the interval is an integral divisor of one day then a new file will always start at midnight. The interval can be given as a plain number of seconds, but a convenient scaled notation is supported: `[Nw][Nd][Nh][Nm][N[s]]`, eg, `2h40m20s` means two hours plus 40 minutes plis 20 seconds. * `log.file.rotate` If non zero, then old log files are deleted so that no more than this many files exist at one time. Every log message is written to all destinations according to their configuration. Network interfaces ------------------ The **servald** daemon periodically scans its operating system's network interfaces and uses its `interfaces` configuration option to select which to ignore and which to use. For example, the following configuration will use any interface whose name starts with `eth` (eg, `eth0`, `eth1`) on port 7333 and any interface whose name starts with `wifi` or `wlan` but is not `wifi0` or `wlan0` as a [Wi-Fi][] on the default port number: $ servald config set interfaces.0.match 'eth*' \ set interfaces.0.type ethernet \ set interfaces.0.port 7333 \ set interfaces.1.match 'wifi0,wlan0' \ set interfaces.1.exclude true \ set interfaces.2.match 'wifi*,wlan*' \ set interfaces.2.type wifi The following configuration is equivalent to the above example, but uses the “legacy”, single-option syntax (see below): $ servald config set interfaces \ '+eth=ethernet:7333,-wifi0,-wlan0,+wifi=wifi,+wlan=wifi' The following two equivalent configurations will use all available interfaces, treating all as Wi-Fi (the default type) with a 400 µs inter-packet delay (the default packet interval for Wi-Fi): $ servald config set interfaces.0.match '*' $ servald config set interfaces '+' Network interface rules ----------------------- As shown in the first example above, the `interfaces` config option contains a numbered list of *rules* that are applied to all detected system interfaces in order of ascending number. The general form of an interface rule is: interfaces.UINT.match=PATTERN[, PATTERN ...] interfaces.UINT.file=PATH interfaces.UINT.exclude=BOOLEAN interfaces.UINT.socket_type=SOCKTYPE interfaces.UINT.port=PORT interfaces.UINT.encapsulation=ENCAPSULATION interfaces.UINT.default_route=BOOLEAN interfaces.UINT.prefer_unicast=BOOLEAN interfaces.UINT.send_broadcasts=BOOLEAN interfaces.UINT.type=IFTYPE interfaces.UINT.mdp_tick_ms=UINT_NONZERO interfaces.UINT.packet_interval=UINT_NONZERO where: * PATTERN is a [shell wildcard][] pattern * BOOLEAN is `true`, `false`, `1`, `0`, `yes`, `no`, `on` or `off` * SOCKTYPE is `dgram`, `stream` or `file` * ENCAPSULATION is `overlay` or `single` * IFTYPE is `wifi`, `ethernet`, `catear` or `other` * PORT is an unsigned decimal integer in the range 1 to 65535 * UINT is any unsigned decimal integer (with no `+` or `-` prefix) * UINT\_NONZERO is an unsigned decimal integer ≥ 1 * PATH is an absolute or relative file path * IN\_ADDR is an Internet address as accepted by [inet_aton(3)][], ie, `N.N.N.N` where `N` is an integer in the range 0 to 255. The `match` and `file` options are mutually incompatible. If both are set, it is an error; the interface rule is omitted from the configuration and `serval.conf` is treated as defective (see above). If neither are set, it is also an error. If a rule specifies a `match` option, then each PATTERN is applied to the names of the real system interfaces using the [fnmatch(3)][] standard library function. If any PATTERN matches, then the rule's `exclude` option is checked: if true, then the interface is not activated, otherwise a socket on that system interface is opened and the interface's `socket_type` is set to `dgram`. (It is invalid to explicitly set `socket_type` to other than `dgram` for a match interface.) If a rule specifies a `file` path, then an interface is created *if the given file exists*. The interface's `socket_type` determines how the file is written and read: * `file` (the default) creates a “dummy” interface for closed communication with other **servald** daemons on the same host -- see below. If the file does not exist, a warning is logged and the interface is not activated. * `stream` reads and writes the file as though it were a [character special device][]. If the file does not exist, an error is logged and the interface is not activated. * `dgram` is not valid for a file interface. The `type` option only affects the default settings the `packet_interval` and `mdp_tick_ms` options, for convenience. In future it may also change the way the interface behaves, for example, an `ethernet` interface may automatically assume that broadcast packets will be filtered out, so will start using MDP unicast protocols immediately rather than waiting to detect that broadcast packets are not acknowledged. The `packet_interval` option controls the maximum rate at which packets are tramsmitted on the interface. It sets the *average* interval, in microseconds, between individual packets. If the interval is less than the time it takes to transmit a packet, then packets will be sent at maximum speed with no intervening delay. Otherwise, delays are inserted between packets as needed to keep to the average. The `mdp_tick_ms` option controls the time interval, in milliseconds, between MDB broadcast announcements on the interface. If set to zero, it disables MDP announcements altogether on the interface (called “tickless” mode). If not set, then the value of the `mdp.iftype.IFTYPE.tick_ms` option is used. If that is not set, then **servald** uses a built-in interval that depends on the IFTYPE. The `encapsulation` option controls how MDP packets are written to the interface's socket: * `overlay` (the default) stuffs as many MDP packets as it can into each [UDP][] frame, to avoid wasting bandwidth on conventional [Wi-Fi][] interfaces which have a fixed packet size (the [IEEE 802.11][] [MTU][]) over the air; * `single` sends each MDP packet on its own to the socket using [SLIP][] encoding, and is suited to data links with a variable packet size on the air (eg, a serial connection to a [packet radio][] modem). The `default_route` option, if true, causes all MDP packets with an unresolved recipient address (SID) to be sent to this interface instead of just dropped. This will allow the node to use [Serval Infrastructure][] to route its packets. Many interfaces may have the `default_route` set to true, but only the first one will be used as the default route. The `prefer_unicast` option, if true, causes the interface to send to unicast IP addresses instead of the broadcast IP address if both have been observed to reach the destination. The `send_broadcasts` option, if false, prevents the interface from sending any broadcast packets whenever a recipient address (SID) cannot be resolved to an interface. Normally, any MDP packet to an unresolvable recipient gets broadcast on all active interfaces. Network interface “legacy” syntax --------------------------------- Instead of using the multi-option schema described above, the `interfaces` configuration option can be set using a less capable “legacy” format, for compatibility with older config files. The “legacy” interfaces syntax is a single text string consisting of a comma-separated list of rule stanzas, each stanza having one of the following forms: + - +PREFIX=IFTYPE +PREFIX=IFTYPE:PORT +PREFIX=IFTYPE:PORT:IGNORED -PREFIX +>PATH The rule `+` matches all interfaces. The rule `-` excludes all interfaces. Rules beginning with `+PREFIX` match any interface whose name starts with `PREFIX`; so for example a rule starting with `+foo` is equivalent to a `match` option with a single PATTERN of `foo*` The rule `-PREFIX` excludes interfaces whose name starts with `PREFIX`. The rule `+>PATH` specifies a dummy interface (see below) with no address or netmask or broadcast filter. Interface rules are numbered in the order they appear, and are applied in that order. For example, an `interfaces` option of `+,-eth0` will not reject the *eth0* interface because the leading `+` will match it first, but `-eth0,+` will reject *eth0* and accept all others. The “legacy” format is only provided for backward compatibility and will eventually be deprecated and removed. The “legacy” interfaces configuration is incompatible with the modern form; an instance that uses one cannot use the other. Dummy network interface ----------------------- Sometimes it is helpful to run an isolated group of connected **servald** instances on a single machine for testing purposes. To make this possible, **servald** supports a *dummy* network interface. A dummy interface is simply a regular file to which all instances append their network packets. The file grows without limit. Each instance advances its own read pointer through the file, packet by packet, skipping packets which are not addressed to it. A single dummy file simulates a lossless mesh network with total connectivity, ie, all nodes that read and write the file are neighbours. To use a dummy interface, first create an empty file, eg, `/tmp/dummy`, and for each servald instance, include the dummy file in its *interfaces* list, eg: $ servald config set interfaces.0.file '/tmp/dummy' NOTE: Because dummynets are files, not sockets, the [poll(2)][] system call does not work on them. As a result the **servald** daemon main loop has slightly different behaviour and timing characteristics when a dummynet is in use. If a dummy interface's `file` PATH is not absolute (ie, does not start with `/`) then it is interpreted relative to the instance directory. The following config options adorn a dummy interface with properties that real interfaces normally obtain directly from the operating system: interfaces.UINT.dummy_address=IN_ADDR interfaces.UINT.dummy_netmask=IN_ADDR interfaces.UINT.drop_unicasts=BOOLEAN interfaces.UINT.drop_broadcasts=BOOLEAN The `dummy_address` option sets the interface's unicast (receive) IP address. The `dummy_netmask` option sets the interface's unicast (receive) IP network mask, which together with `dummy_address` determines the interface's IP broadcast address. The `drop_unicasts`, option, if true, will drop overlay frames addressed to the interface's unicast IP address, so that only broadcast packets will be read. The `drop_broadcasts`, option, if true, will drop overlay frames addressed to the interface's broadcast IP address, so that only unicast packets will be read. This can simulate the effects of the Fi-Fi drivers on some Android devices that filter out broadcast packets (to prevent the device from waking up unless there is traffic explicitly sent to it). [Serval Project]: http://www.servalproject.org/ [Serval Infrastructure]: ./Serval-Infrastructure.md [US-ASCII]: http://en.wikipedia.org/wiki/ASCII [Bourne shell]: http://en.wikipedia.org/wiki/Bourne_shell [isspace(3)]: http://linux.die.net/man/3/isspace [shell wildcard]: http://www.kernel.org/doc/man-pages/online/pages/man7/glob.7.html [open(2)]: http://www.kernel.org/doc/man-pages/online/pages/man2/open.2.html [write(2)]: http://www.kernel.org/doc/man-pages/online/pages/man2/write.2.html [poll(2)]: http://www.kernel.org/doc/man-pages/online/pages/man2/poll.2.html [fnmatch(3)]: http://www.kernel.org/doc/man-pages/online/pages/man3/fnmatch.3.html [inet_aton(3)]: http://www.manpagez.com/man/3/inet_aton [Wi-Fi]: http://en.wikipedia.org/wiki/Wi-fi [IEEE 802.11]: http://en.wikipedia.org/wiki/IEEE_802.11 [UDP]: http://en.wikipedia.org/wiki/User_Datagram_Protocol [MTU]: http://en.wikipedia.org/wiki/Maximum_transmission_unit [SLIP]: http://en.wikipedia.org/wiki/Serial_Line_Internet_Protocol [packet radio]: http://en.wikipedia.org/wiki/Packet_radio [character special device]: http://en.wikipedia.org/wiki/Device_file#Character_devices