1. AppCenter is empty, only the installed software is shown.
  2. I can't add repositories. I get the message 'sudo: add-apt-repository: command not found'.
  3. sudo apt install software-properties-common doesn't work either. I get the message 'E: Unable to locate package software-properties-common'
  • i have the sames problems... i cant install anything and i cant add repos... what i do a operating system if i cant install my apps? no gparted no clementine no steam no chromium no easytag no no no no... the command sudo apt-get update dont solve the problem mate...! now i see here blog.elementary.io/post/145881464631/loki-beta to say no unsafe software source... someone else will decide for me what is safe and what is not..? reminds me microsoft and osx – Arktika 13 Sep 10 '16 at 13:20
  • Do you have ipv6? It might be the problem. – cristian mos Sep 10 '16 at 14:42
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  • I tried Ubuntu 16.04 and Linux Mint 18 KDE and the symptoms are the same (some websites don't load, update doens't work). I'm almost certain that it's a network manager and/or ipv6 problem on a pppoe (dsl) connection. In Freya ipv6 is ignored by default. In Loki I'm connecting with ipv6 by default, and I wasn't able to disable it yet with several methods found over the internet. – cristian mos Sep 11 '16 at 9:24
  • So I solved it. I needed to add the line "mtu=1492" in the file /etc/NetworkManager/system-connections/*Connection name* like this: [ppp] lcp-echo-failure=5 lcp-echo-interval=30 mtu=1492 After making the DSL connection at first, of course. IPv6 doesn't need to be stopped. Then reboot and updates are working, and software is visible in AppCenter. – cristian mos Sep 14 '16 at 13:56

I had this too. To fix run sudo apt update

Once it's done you can add PPAs after installing software-common-properties, although this is not recommended to ensure security and stability.

  • sudo apt-get update doesn't work either: E: Could not get lock /var/lib/apt/lists/lock - open (11: Resource temporarily unavailable) E: Unable to lock directory /var/lib/apt/lists/ – cristian mos Sep 10 '16 at 8:07
  • So I killed all the apt processes and removed /var/lib/apt/lists/lock and /var/cache/apt/archives/lock. sudo apt-get update initiated, but it's very, very slow. After 1 hour and a half it still didn't finish, so I closed it. I was looking for a solution to speed it up, but couldn't find any (Epiphany is not opening all pages). – cristian mos Sep 10 '16 at 10:48
  • Maybe reboot? Sounds like something might be getting held onto by the system and preventing you from moving forward. Otherwise maybe try to reinstall. – Jason Lucero Sep 10 '16 at 13:18
  • I reinstalled and it's the same. It might just be an ipv6 problem, but I'm not sure, because also some websites don't load. I don't know if I properly disabled ipv6. – cristian mos Sep 10 '16 at 14:38

AppCenter displayed the installed apps only. Running sudo apt update did not solve the problem. I had to reinstall AppCenter to fix it.

  1. Remove AppCenter:

    sudo apt purge appcenter

  2. Reboot

  3. Install AppCenter:

    sudo apt install appcenter

  4. Update repositories:

    sudo apt update

  5. Open AppCenter.

  • I also had to resolve any repository related errors which were listed by apt-get udpate. Might be worth adding that to the answer – codecowboy Apr 23 '17 at 8:28

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