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I'm using Ubuntu 14.04 on a Toshiba S55-B5289 laptop. I've been using a second monitor with the laptop since I got it, and it's basically been plug-and-play. I connect the monitor via HDMI, and usually it just fires right up. Last night, I unplugged the monitor to take the computer upstairs. I noticed it was still behaving as if the second monitor was there. So I logged out and logged back in--problem solved. Today, I plug the monitor back in, and Ubuntu doesn't detect it. I've spent the last half hour unplugging, plugging back in, restarting, tweaking settings, and browsing forums without much luck. Most of the tips seem to have to do with getting a second monitor working in the first place. It was working yesterday. But now the laptop just doesn't seem to notice it's there.

  • I just learned this trick which helped with some of my multiple monitor issues: connect both monitors, then repeatedly press magic-p to cycle through different configurations. – Organic Marble Apr 7 '15 at 0:12
  • magic-p? Can't say I know what that is. – tmoore82 Apr 7 '15 at 0:15
  • "Magic" = "windows" key on most keyboards. Also called super – Organic Marble Apr 7 '15 at 0:16
  • Gotcha. When I git magic-p, I just see a list of numbers/letters pop up on my shortcuts bar. – tmoore82 Apr 7 '15 at 0:18
  • Odd. It cycles through 3 or 4 different monitor configs for me. Sorry it didn't help. – Organic Marble Apr 7 '15 at 0:19
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Some system updates came out today, and I applied those using Synaptic Package Manager. After the update and another reboot, the dual-monitor system is working again. I don't see anything in the updates that appear to have anything to do with display, but my guess is that maybe running the updates flushed out whatever the disconnect was that was keeping the second monitor from being picked up.

  • To avoid this problem in the future, could you post your monitors.xml to paste.ubuntu.com as I've got a hunch the problem is somewhere in there... ;-) – Fabby Apr 11 '15 at 9:04
  • paste.ubuntu.com/10819346 – tmoore82 Apr 14 '15 at 0:07
  • As I suspected... I'll start answering in a few minutes. – Fabby Apr 14 '15 at 0:10
  • any feed-back??? – Fabby Apr 14 '15 at 0:31
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As I suspected, this was no fluke: Your monitors.xml contained an erroneous configuration without HDMI.

Here is the corrected version that only contains one single configuration (the original that worked without any problems)

Now

  1. Replace your existing version with my corrected one
  2. Keep a back-up of the corrected just in case this ever happens again…
  • Not sure I understand. I can see that mine had the configuration repeated, but there was an HDMI configuration in it. Your version deleted the repeated info, but it didn't add anything. Or am I missing something? – tmoore82 Apr 14 '15 at 1:12
  • As you can see from my answer, I'm not currently having the problem. I wasn't having the problem when you submitted your answer. I can't confirm that this solves it. The problem was solved for me when I ran new updates. If/when it happens again, I will try your solution. If it works, I'll mark your answer as correct. – tmoore82 Apr 15 '15 at 14:03
  • Fair enough! ;-) Please delete all comments as they've been incorporated into the answer anyway... – Fabby Apr 15 '15 at 17:40
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By sheer coincidence I had a similar problem right here with this computer only yesterday. Believing in trying the simplest solution first I applied a thin layer of CAIG DeOxit D100L to both ends and that fixed it. I recommend it to all my friends.

I gave a vial of this to my girlfriend two years ago, and of all the gifts I've given her for birthdays, holidays, and anniversaries, I'm sorry to say this is what she uses the most. A few months ago she "fixed" her daughter's iphone when it refused to charge merely dabbing this on the charger plug. When her 14 year old daughter asked how that fixed it, my girlfriend's response was "It's Magic".

So you see, while this is not the same magic recommended by another, it is a useful tool necessary in any geek's arsenal, and it is available online.

  • I appreciate the tip. The cable/monitor work fine when plugged into another computer. Do you think this is still a possible solution? – tmoore82 Apr 7 '15 at 23:25
  • If the cable and monitor worked with another computer, but previously worked fine with the original computer, then the problem exists in the original computer. DeOxit might fix it, if it is only the connection. I carry a vial of deoxit in my fanny pack at all times. Let me give you a quick example. The last time I mailed a package at the post office, the scanner stopped working and the clerk could not shift machines. With the line getting longer and the clerk consenting, I fixed the scanner with my deoxit, right there. He took note of it to buy some himself. – gyropyge Apr 8 '15 at 5:51

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