I saw a lot of questions regarding this, but mine seems a little different.
Here's what I receive:
/etc/cron.weekly/apt-xapian-index: FATAL -> Failed to fork. run-parts: /etc/cron.weekly/apt-xapian-index exited with return code 100
/etc/cron.daily/apt: FATAL -> Failed to fork.
/etc/cron.daily/apt: DB Update failed, database locked
I always have at least 600 MB of free RAM.
If I try to manually run
sudo /etc/cron.daily/apt nothing happens.. the shell hangs.
What could be the problem?
EDIT: Ubuntu Server 14.04