dbus启动失败：Couldn't connect to system bus: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11

在没有开启x窗口的shell下启动dbus相关程序时会如上错误，详细原因如下：

This is not considered to be a bug. Auto-launching D-Bus sessions when
not under X11 would result in one new D-Bus session per application that
tried to use it, unable to communicate with other user-facing
applications that do not share that session; those sessions would also
never exit, leaving unused dbus-daemon and dbus-launch processes
building up indefinitely (until the next reboot). That‘s clearly not
useful or desirable, but in the absence of a clear and
machine-detectable definition of "session" we can‘t really improve on
it. (Under X11, the lifetime of the X server acts as the definition of
the session, so autolaunching can work and is useful.)

Applications that can usefully be run either with or without a D-Bus
session, such as pulseaudio, should treat errors in connecting to the
session bus as non-fatal, and continue to have the rest of their
functionality. I believe PA already does this, in fact; that message in
your syslog just tells you that the D-Bus part of its functionality will
not be active.

If you do need to start a D-Bus session while not under X11, you can run
dbus-launch as documented in the dbus-launch(1) man page, something like
this:

if test -z "$DBUS_SESSION_BUS_ADDRESS" ; then
        eval `dbus-launch --sh-syntax`
        echo "D-Bus per-session daemon address is:"
        echo "$DBUS_SESSION_BUS_ADDRESS"
    fi

in which case you‘re responsible for getting the
DBUS_SESSION_BUS_ADDRESS environment variable to all the processes that
should share the session, and managing the lifetime of the session (i.e.
killing the session‘s dbus-daemon when appropriate). I have sent patches
upstream to add a dbus-run-session tool that runs a session for as long
as its child process is running and then terminates it (similar
semantics to schroot), but they haven‘t been merged yet.

Older versions of dbus-launch tried to monitor the lifetime of text
login sessions on virtual consoles, but the way they did that would
consume every second character of input (Debian bug #453755) and it
isn‘t clear whether it actually ended the session on logout either. This
was fixed by several changes between squeeze and wheezy.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=690530

解决办法：

先执行命令

eval `dbus-launch --sh-syntax`

在运行dbus程序即可。

dbus启动失败：Couldn't connect to system bus: Unable to autolaunch a dbus-daemon without a $DISPLAY for X11