Avahi

2012-01-14T11:35:20Z

Nathanhammond: Note an issue in installing via command line.

=Avahi=
[http://avahi.org Avahi] is a Linux service for providing multicast-DNS/DNS-SD (also known as [http://en.wikipedia.org/wiki/Bonjour_%28software%29 Bonjour] or mDNS/DNS-SD). Avahi allows for simple service discovery and advertisement on a local network and provides name resolution for all hosts running a mDNS/DNS-SD service.

Using Avahi allows for easy SSH access, among other things, over a local wireless network. Once installed and started, users can ssh to their device using their mDNS assigned hostname.

==Avahi Installation==

For 2.x and 3.x devices, avahi can be found in the alpha repo, any other devices install via ipkg as follows:

First, use novacom to access the Pre and install the Avahi ipkg.

$> sudo /opt/bin/ipkg-opt install avahi

Avahi seems to want to run as a user named "avahi". To create the user, run the following command:

$> adduser -h /opt/var/run/avahi avahi

Avahi currently attempts to access a different dbus system socket than the one provided by the Pre's dbus, it is possible to start Avahi with dbus support by creating a symbolic link from palm dbus directory to the /opt dbus directory and starting avahi daemon with root privileges. According to the Avahi website, however running avahi-daemon with root privileges is not recommended.

The following command will create a symbolic link to /opt dbus directory to palm dbus directory:

ln -s /var/run/dbus /opt/var/run/dbus

if preferred avahi can be be ran without dbus support by editing <tt>/opt/etc/avahi/avahi-daemon.conf</tt> and make the following change:

Replace this line:
#enable-dbus=yes

With this line:
enable-dbus=no

However, this does not allow the use of avahi commands such as avahi-browse, avahi-publish etc...

At this point, the Avahi daemon can be started with root privileges and dbus support with the following command:

$> /opt/sbin/avahi-daemon --no-drop-root

If you disabled dbus support however it is recommended to run Avahi daemon without root privileges using the following command:

$> /opt/sbin/avahi-daemon

If you would like Avahi to start up at boot, create the following two files:

'''/opt/etc/init.d/S60avahi'''
#!/bin/sh

[ -e /opt/etc/default/avahi ] && . /opt/etc/default/avahi

if [ "$AVAHI_ENABLE" = "no" ]; then
exit
fi

if [ -n "`pidof /opt/sbin/avahi-daemon`" ]; then
killall /opt/sbin/avahi 2>/dev/null
fi

/opt/sbin/avahi-daemon -D

'''/opt/etc/default/avahi'''
AVAHI_ENABLE=yes

Make sure you set the startup script to executable:

$> chmod 755 /opt/etc/init.d/S60avahi

Alternatively, you can create an upstart script at '''/etc/event.d/avahi-daemon''':
# avahi-daemon - mDNS/DNS-SD daemon
#
# The Avahi daemon provides mDNS/DNS-SD discovery support (Bonjour/Zeroconf)
# allowing applications to discover services on the network.

description "mDNS/DNS-SD daemon"

start on started LunaSysMgr
respawn

console none

exec /opt/sbin/avahi-daemon

NOTE 1: This script is not being stored in the /opt directory. You may have to replace it after an update, and it may cause problems with your Pre.

NOTE 2: You may find your device appearing at '''hostname-4.local''' instead of simply '''hostname.local'''. Restarting avahi-daemon (stop avahi, start avahi) will fix that. You could also figure out the root cause for that problem and address it in a pre-start block in the upstart script.

NOTE 3: The Preware alpha feed approach creates a similar upstart script at '''/var/palm/event.d/org.webosinternals.avahi-daemon'''

==Connecting via SSH using mDNS==

mDNS uses the system's hostname and appends it to the <tt>local.</tt> domain. Using the Pre's default <tt>palm-webos-device</tt> hostname, the following command would be used to SSH to your Pre on port 222:

$> ssh -P 222 palm-webos-device.local.

If you are using an OpenSSH key to connect:

$> ssh -i /path/to/ssh/key palm-webos-device.local.

'''Note: The system that you are connecting from MUST have a mDNS service also running, else the hostname will not resolve'''

==Current Issues on the Pre==

* The ipkg binary of Avahi attempts to find the dbus socket at <tt>/opt/var/run/dbus/system_bus_socket</tt>, but the Pre's dbus socket is at <tt>/var/run/dbus/system_bus_socket</tt>. I have detailed a solution by running Avahi with root privileges however an approach which allow it to run after dropping root privileges is preferred.
* The avahi-daemon seems to have issues keeping the mDNS name resolution running for more than a few minutes. I don't know if this is a power management issue or something else at this point.
* The command line install approach may result in your device appearing at '''hostname-4.local''' due to avahi-daemon believing that your hostname is already claimed on the first run only.

Avahi

2012-01-14T11:30:03Z

Nathanhammond: Update upstart script for command line installation.

WebOS Internals - User contributions [en]

Avahi

Avahi