yum-cron (3.4.3-150.el7.noarch on SL7.3) has stopped working for me. 
There are a bunch of upgrades to be done in sl-fastbugs, but yum-cron 
bombs out with an error message

Traceback (most recent call last):
   File "/sbin/yum-cron", line 729, in <module>
     main()
   File "/sbin/yum-cron", line 726, in main
     base.updatesCheck()
   File "/sbin/yum-cron", line 649, in updatesCheck
     self.installUpdates(self.opts.update_messages)
   File "/sbin/yum-cron", line 570, in installUpdates
     result, err = self.sigCheckPkg(po)
   File "/usr/lib/python2.7/site-packages/yum/__init__.py", line 2758, in sigCheckPkg
     sigresult = rpmUtils.miscutils.checkSig(ts, po.localPkg())
   File "/usr/lib/python2.7/site-packages/rpmUtils/miscutils.py", line 71, in checkSig
     fdno = os.open(package, os.O_RDONLY) OSError: [Errno 2] No such file 
or directory: 
'/var/cache/yum/x86_64/7/sl-fastbugs/packages/lvm2-libs-2.02.166-1.el7_3.5.x86_64.rpm'

/var/cache/yum/x86_64/7/sl-fastbugs/packages is in fact empty, possibly 
as a result of a 'yum clean all'.

It is nothing to do with lvm2-libs specifically.  I can upgrade that 
with yum from the command line.  yum-cron then gives the same error on 
the next package.

I haven't knowingly changed anything away from the default yum or 
yum-cron configuration.  I do notice 'keepcache=0' in /etc/yum.conf, 
while the man page says that the default is 'keepcache=1'.

Any ideas on what could be making yum-cron insist on those cache files 
when yum itself doesn't, and how to change that?

Stephen Isard