在运行docker命令时，我不断收到这样的错误：
$ sudo docker search mattdm/fedora
2014/06/05 22:12:25 Error: Get https://index.docker.io/v1/search?q=mattdm%2Ffedora: x509: certificate signed by unknown authority
我在没有任何http代理的情况下使用Fedora 20 x86_64。
我搜索了谷歌，但没有找到任何线索，并且不知道如何解决这个错误，有人能给我一些提示来解决这个问题吗？
这里有一些额外的信息可能会有所帮助：
$ sudo docker version
Client version: 0.11.1
Client API version: 1.11
Go version (client): go1.2.1
Git commit (client): fb99f99/0.11.1
Server version: 0.11.1
Server API version: 1.11
Git commit (server): fb99f99/0.11.1
Go version (server): go1.2.1
$ curl https://index.docker.io/v1/search?q=mattdm/fedora
{"query": "mattdm/fedora", "num_results": 2, "results": [{"is_trusted": false, "is_official": false, "name": "mattdm/fedora", "star_count": 49, "description": "A basic Fedora image corresponding roughly to a minimal install, minus some things which don't make sense in a container. Use tag `f20` for Fedora 20 or `f19` for Fedora 19."}, {"is_trusted": false, "is_official": false, "name": "mattdm/fedora-small", "star_count": 8, "description": "A small Fedora image on which to build. Contains just enough that you'll be able to run `yum install` in your dockerfiles to create something useful. Use tag `f19` for Fedora 19."}]}
$ ls -l /etc/pki/tls/certs/
total 1500
lrwxrwxrwx. 1 root root 49 Feb 18 03:58 ca-bundle.crt -> /etc/pki/ca-trust/extracted/pem/tls-ca-bundle.pem
-rw-r--r--. 1 root root 713687 Jan 5 2013 ca-bundle.crt.rpmsave
lrwxrwxrwx. 1 root root 55 Feb 18 03:58 ca-bundle.trust.crt -> /etc/pki/ca-trust/extracted/openssl/ca-bundle.trust.crt
-rw-r--r--. 1 root root 796502 Jan 5 2013 ca-bundle.trust.crt.rpmsave
-rw-r--r--. 1 root root 1338 Mar 14 12:13 ca-certificates.crt
-rw-------. 1 root root 1025 Sep 25 2012 localhost.crt
-rwxr-xr-x. 1 root root 610 Apr 8 08:36 make-dummy-cert
-rw-r--r--. 1 root root 2242 Apr 8 08:36 Makefile
-rwxr-xr-x. 1 root root 829 Apr 8 08:36 renew-dummy-cert