Bug 1566125

Fixed in pull request https://github.com/rpm-software-management/dnf/pull/1056

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Still not fixed in FC-27.
(Commenting line "reposdir=" let dnf works, but if line is in place, it crashes)
See below:

$ cat /tmp/test.conf
[main]
cachedir=/var/cache/dnf
debuglevel=2
logfile=/var/log/yume.log
pkgpolicy=newest
tolerant=1
exactarch=1
retries=20
obsoletes=1
reposdir=
gpgcheck=0
plugins=1

[oscar_fc-27-x86_64]
name=fc-27-x86_64 package repository
baseurl=file:/tftpboot/oscar/fc-27-x86_64

[unstable_fc-27-x86_64]
name=fc-27-x86_64 package repository
baseurl=http://svn.oscar.openclustergroup.org/repos/unstable/fc-27-x86_64

[27_x86_64]
name=x86_64 package repository
baseurl=https://dl.fedoraproject.org/pub/fedora/linux/updates/27/x86_64

[x86_64_os]
name=os package repository
baseurl=https://dl.fedoraproject.org/pub/fedora/linux/releases/27/Everything/x86_64/os




$ sudo dnf -c /tmp/test.conf list all
Traceback (most recent call last):
  File "/bin/dnf", line 58, in <module>
    main.user_main(sys.argv[1:], exit_code=True)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 179, in user_main
    errcode = main(args)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 64, in main
    return _main(base, args, cli_class, option_parser_class)
  File "/usr/lib/python3.6/site-packages/dnf/cli/main.py", line 95, in _main
    cli.configure(list(map(ucd, args)), option_parser())
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 818, in configure
    self._read_conf_file(opts.releasever)
  File "/usr/lib/python3.6/site-packages/dnf/cli/cli.py", line 912, in _read_conf_file
    conf._search_inside_installroot('reposdir')
  File "/usr/lib/python3.6/site-packages/dnf/conf/config.py", line 812, in _search_inside_installroot
    val.lstrip('/'))):
AttributeError: 'NoneType' object has no attribute 'lstrip'




$ rpm -q dnf
dnf-2.7.5-2.fc27.noarch

The problem is already fixed in upstream and will be released into rawhide and later on in F28 with dnf-3.0