So I have a Raspberry Pi running Debian and the WebIOPi system. The daemon runs just fine when I start it using a standard start ´$ sudo /etc/init.d/webiopi start´ command but the auto start doesn't work ´$ sudo update-rc.d webiopi defaults´.
The log suggests it is a encoding problem in Python, my guess python is using ascii but the script file is using utf8.
Why does it work normally but not in auto start and what is a good way to fix this?
To confirm the log and your suspicion, this is an encoding issue (bytes vs string most likely). Even if you set the encoding of your file to UTF-8 with # -*- coding: utf-8 -*-, you can still have issues working with text which has been changed from one form to another.
Strings are not really strings, but representations of bytes in a particular order. UTF-8 provides for the encoding of many more characters than ASCII can handle, so if you try to convert a character which exists in a UTF-8 encoded string to an ASCII encoded string, then you will get an error because no such encoding exists.
I cannot give a much better answer without more information, such as code and / or data source.
Reading https://docs.python.org/2/howto/unicode.html#the-unicode-type we learn by studying the following example(s):
>>> unicode('abcdef')
u'abcdef'
>>> s = unicode('abcdef')
>>> type(s)
<type 'unicode'>
>>> unicode('abcdef' + chr(255))
Traceback (most recent call last):
...
UnicodeDecodeError: 'ascii' codec can't decode byte 0xff in position 6:
ordinal not in range(128)
The documentation also mentions that you can choose to handle these exceptions by either replacing or ignoring them, like so:
>>> unicode('\x80abc', errors='strict')
Traceback (most recent call last):
...
UnicodeDecodeError: 'ascii' codec can't decode byte 0x80 in position 0:
ordinal not in range(128)
>>> unicode('\x80abc', errors='replace')
u'\ufffdabc'
>>> unicode('\x80abc', errors='ignore')
u'abc'
NOTE 1: In Python 3 things have changed. for writing code which is compatible with Python 3, I recommend the following read:
https://docs.python.org/3.0/whatsnew/3.0.html#text-vs-data-instead-of-unicode-vs-8-bit
NOTE 2: It is also worth noting that if your encoding issue is encountered while trying to display the string on the console then, python has a -u switch which can be used in certain situations, such as when you are serving a binary file through a CGI script, which will turn off buffering of strings, but that opens up another can of worms. But, none the less, mimicking this behavior without invoking -u:
>>> print 'test'
'test'
>>> import os
>>> import sys
>>> sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
>>> print 'test'
test
This truly depends on that program.
However if there's a difference between starting it manually and as a part of system startup, then the core difference ought to be in environment variables. This typical for e.g. inittab.
Two options here -- either your locale is not set up, or script ends up using different version of python.
For the earlier, consider adding LANG (precise) or if needed LC_ALL (a hammer) to this script or global environment for all startup tasks.
You can try manually by comparing these two invocations:
sudo LC_ALL=en_US.UTF-8 /etc/init.d/webiopi start
vs.
sudo LC_ALL=C /etc/init.d/webiopi start
For the latter try changing PATH to only include some of /bin:/usr/bin:/usr/local/bin
