Version-Release number of selected component:
dnf-0.6.4-1.fc21

Additional info:
reporter:       libreport-2.3.0
cmdline:        /usr/bin/python -OO /bin/dnf -y update
executable:     /bin/dnf
kernel:         3.18.7-200.fc21.x86_64
runlevel:       N 5
type:           Python
uid:            0

Truncated backtrace:
lock.py:85:_try_read_lock:ValueError: invalid literal for int() with base 10: ''

Traceback (most recent call last):
  File "/bin/dnf", line 36, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 182, in user_main
    errcode = main(args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 84, in main
    return _main(base, args)
  File "/usr/lib/python2.7/site-packages/dnf/cli/main.py", line 134, in _main
    cli.run()
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 1063, in run
    self._process_demands()
  File "/usr/lib/python2.7/site-packages/dnf/cli/cli.py", line 785, in _process_demands
    load_available_repos=lar)
  File "/usr/lib/python2.7/site-packages/dnf/base.py", line 227, in fill_sack
    with lock:
  File "/usr/lib/python2.7/site-packages/dnf/lock.py", line 106, in __enter__
    pid = self._try_read_lock()
  File "/usr/lib/python2.7/site-packages/dnf/lock.py", line 85, in _try_read_lock
    return int(f.readline())
ValueError: invalid literal for int() with base 10: ''

Local variables in innermost frame:
self: <dnf.lock.ProcessLock object at 0x7f00407186d0>
f: <closed file u'/var/cache/dnf/x86_64/21/x86_64/21/metadata_lock.pid', mode 'r' at 0x7f00402c1db0>

Potential duplicate: bug 1195956