I managed to fix the issue. The problem was due to sudo as Alexander 
pointed out. For some reasons, sudo without password was not working 
correctly with that configuration provided in the docs.

I added this line

/user ALL=(ALL) NOPASSWD:ALL/

below the sudo group section in /etc/sudoers and then it started to work.

I'm glad it has now been solved.
Thank you all

Frank

On 18/04/2018 13:15, Claudius Heine wrote:
> Hi Frank,
>
> On 2018-04-18 13:08, Francesco wrote:
>> Thanks for your replies. I just checked the BBMULTICONF variable in 
>> local.conf and it is there.
>>
>> Unfortunately If i now try to run  bitbake 
>> multiconfig:qemuarm-jessie:isar-image-base I stil get the same error.
>
> Your error does look interesting. I would think that somehow your 
> sudoers setting doesn't work correctly. Maybe try that out. It 
> shouldn't ask for your password.
>
> Otherwise I can suggest building isar inside a container such as:
>
>     https://hub.docker.com/r/kasproject/kas-isar/
>
> The system settings and basic dependencies are already setup there.
> You just need to start it like this:
>
> sudo docker run -v $(pwd):/mnt:rw -e USER_ID=$(id -u) 
> --cap-add=SYS_ADMIN --cap-add=MKNOD --security-opt=seccomp:unconfined 
> --privileged --device $(sudo /sbin/losetup -f) -rm -ti 
> kasproject/kas-isar:latest bash
>
> And it should work.
>
> Cheers,
> Claudius
>
>>
>> Frank
>>
>>
>> On 18/04/2018 13:03, Jan Kiszka wrote:
>>> On 2018-04-18 13:01, Claudius Heine wrote:
>>>> Hi,
>>>>
>>>> On 2018-04-18 12:56, [ext] Jan Kiszka wrote:
>>>>> On 2018-04-18 12:50, Francesco wrote:
>>>>>> Hello everyone,
>>>>>>
>>>>>> I'm new to isar and today I made an attempt to build the default 
>>>>>> image
>>>>>> with it. I installed all the host tools necessary as it is 
>>>>>> written in
>>>>>> the docs. Then I followed strictly the doc/user_manual.
>>>>>>
>>>>>> My host OS is debian jessie.
>>>>>>
>>>>>> Unfortunately when I try to build an image I get this error:
>>>>>>
>>>>>> /bitbake isar-image-base//
>>>>> In that case, you are not using the multiconfig files Isar ships and
>>>>> have to replicate all required settings into your local.conf. I would
>>>>> rather recommend
>>>>>
>>>>> bitbake multiconfig:qemuarm-jessie:isar-image-base
>>>>>
>>>>> That will work (is also part of CI).
>>>> You also need to set the BBMULTICONF variable in local.conf.
>>>>
>>> Good point! I'm too much used to kas descriptions by now. ;)
>>>
>>> Jan
>>>
>>>> Maybe just follow this:
>>>>
>>>> https://github.com/ilbers/isar/blob/53ed253/doc/user_manual.md#building-target-images-for-multiple-configurations 
>>>>
>>>>
>>>>
>>>> And just use one configuration.
>>>>
>>>> The documentation about 'One configuration' is not really up-to-date.
>>>>
>>>> Cheers,
>>>> Claudius
>>>>
>>
>