└─▪  youtube-dl -v 'https://www.youtube.com/watch?v=gUfV8ifh94w'
[debug] System config: []
[debug] User config: []
[debug] Command-line args: [u'-v', u'https://www.youtube.com/watch?v=gUfV8ifh94w']
[debug] Encodings: locale UTF-8, fs UTF-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2015.09.09
[debug] Python version 2.7.6 - Linux-3.16.0-38-generic-x86_64-with-LinuxMint-17.2-rafaela
[debug] exe versions: avconv 9.18-6, avprobe 9.18-6
[debug] Proxy map: {}
[youtube] gUfV8ifh94w: Downloading webpage
[youtube] gUfV8ifh94w: Downloading embed webpage
[youtube] gUfV8ifh94w: Refetching age-gated info webpage
ERROR: gUfV8ifh94w: YouTube said: Please sign in to view this video.
Traceback (most recent call last):
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 660, in extract_info
    ie_result = ie.extract(url)
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 287, in extract
    return self._real_extract(url)
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/youtube.py", line 1075, in _real_extract
    expected=True, video_id=video_id)
ExtractorError: gUfV8ifh94w: YouTube said: Please sign in to view this video.