Configuring servald
===================
[Serval Project][], April 2013

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 options
---------------------

The **servald** configuration is an unordered set of label-value pairs called
*options*.

An option *label* is a sequence of one or more alphanumeric words separated by
period characters, eg, `log.file.directory_path`.

An option *value* is a string of characters which is parsed according to the
option's type, for example:

  * decimal integer `10` `0` `-1000000`
  * boolean `true` `false` `on` `off` `1` `0` `yes` `no`
  * internet address (in\_addr) `192.168.1.1`
  * time interval `12h` `1w3d` `2h15m30s`
  * absolute path `/var/lib/serval`
  * relative path `../lib/hostlist`
  * Serval ID (SID) `EEBF3AC19E7EE58722A0F6D4A4D5894A72F5C71030C3399FE75808DCF6C6254B`
  * scaled integer: a decimal integer with an optional scale suffix, one of `k`
    (10^3), `K` (2^10), `m` (10^6), `M` (2^20), `g` (10^9) or `G` (2^30), eg
    `1.5m` = 1,500,000

If a value does not parse correctly, it is *invalid*.

Instance path
-------------

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 --enable-instance-path=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.

Running many daemons
--------------------

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.

Configuration persistence
-------------------------

**servald** stores its configuration option settings in a file called
`serval.conf` in its instance directory, which it reads upon every invocation.
This means that each instance's own option settings persist until changed or
until its `serval.conf` file is altered or removed.

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 syntactically malformed file or an unsupported
or invalid option:

 * If `serval.conf` is syntactically malformed, then **servald** will log a
   warning, skip the malformed line and continue parsing;

 * If an unsupported configuration option is encountered (which could be a mis-
   spelling of a proper option), then **servald** will log a warning and
   ignore the option, leaving it with the built-in default value;

 * If a configuration option has an invalid value, then **servald** will log
   a warning and ignore the option, leaving it with the built-in default value.

In all the above cases, most **servald** commands will reject the defective
file: they will log an error and exit with error status (255).  The logging is
done using options salvaged from the defective file (see the `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.

Invalid configuration of daemons
--------------------------------

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.

Configuration commands
----------------------

To set a configuration option:

    $ servald config set name.of.option 'value'
    $

To unset (remove) a configuration option, returning it to its default value:

    $ servald config del name.of.option
    $

To examine an option's current value as defined in the `serval.conf` file
(even invalid and unsupported options may be examined):

    $ servald config get name.of.option
    name.of.option=value
    $

To examine all option settings defined in the `serval.conf` file, including
invalid and unsupported options:

    $ servald config get
    interfaces=+eth0,+wifi0
    name.of.option=value
    name.of.other_option=value2
    $

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.

To examine all current *valid* configuration option settings, as produced by
parsing `serval.conf` and omitting invalid and unsupported 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::1m,+wlan=wifi::1m'

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* delay in microseconds
between individual packets.  This delay is only applied after a 5 ms burst of
consecutive packets with no delay.

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
[Bourne shell]: http://en.wikipedia.org/wiki/Bourne_shell
[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