ImportError: cannot import name 'spawn'

Thanks Jema.
But there is another error. I think it is about database problem but I don't understand why it happened.

for MACHINE in qemux86 ; do . ./oe-init-build-env && bitbake webos-image; done
Altered environment for qemux86@webos development
ERROR: Error parsing configuration files
Traceback (most recent call last):
File "/home/[USER]/webOS_env/build-webos/bitbake/lib/bb/cookerdata.py", line 268, in CookerDataBuilder.parseBaseConfiguration():
if self.data.getVar("BB_WORKERCONTEXT", False) is None:
> bb.fetch.fetcher_init(self.data)
bb.codeparser.parser_cache_init(self.data)
File "/home/[USER]/webOS_env/build-webos/bitbake/lib/bb/fetch2/init.py", line 504, in fetcher_init(d=<bb.data_smart.DataSmart object at 0x7f5bf363e860>):
pass
> revs.clear()
else:
File "/home/[USER]/webOS_env/build-webos/bitbake/lib/bb/persist_data.py", line 147, in SQLTable.clear():
def clear(self):
> self._execute("DELETE FROM %s;" % self.table)

File "/home/[USER]/webOS_env/build-webos/bitbake/lib/bb/persist_data.py", line 66, in SQLTable._execute(*query=('DELETE FROM BB_URI_HEADREVS;',)):
try:
> return self.cursor.execute(*query)
except sqlite3.OperationalError as exc:
sqlite3.OperationalError: attempt to write a readonly database

Makefile:42: recipe for target 'webos-image' failed
make: *** [webos-image] Error 1