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My ex set up my computer and is a little possessive still. I want to make sure they can't monitor my computer usage, access files, etc. I wonder if there is a blanket setting in system preferences or something that I can use to decline/ reset all ssh permissions? I'm concerned they may have installed some kind of back door or something, with all good intentions at first for being able to help me out maybe, and I don't really know what I'm looking for. I'm running Kubuntu, the most updated version, and don't know any of the lingo or jargon. I just want to make sure my computer is closed to the outside.

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    Then you have to reinstall the whole system. – Ipor Sircer Sep 18 '18 at 6:57
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    To those who confirmed a system reinstallation is the only fix - thanks for your help! I'm comfortable with reinstalling the system - I've just installed Xubuntu on a new-to-me laptop - but just didn't want to go to the trouble if there was something in system settings or some kind of command line jingo that would reset to a default for remote access. – user311397 Sep 18 '18 at 18:01
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    @RuiFRibeiro You say that this forum is "not intended for... end user support". But everyone who uses Linux is an end user. My question was not generic, nor was it a broad request: it was highly specific, as evidenced by the number of concise and specific answers it garnered and the absence of anyone thinking I was asking something else or asking for clarification. It sounds like you're really saying "non experts are unwelcome here." But so many people welcomed and answered my question before you started posting complaints about it! – user311397 Sep 18 '18 at 18:10
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    @RuiFRibeiro you really should understand the scope of this site better before presuming to tell others what is and is not on topic. This site is for beginners and experts, not for experts only. And it has always been that way. All of us started out as newbies and if only experts were to use this site, we'd all be staring at a blank page waiting for questions which never came. user311397 please don't think that a few users speak for all of us. While we do require questions to be clear enough to be answerable, that does not mean we expect users to be experts. – terdon Sep 18 '18 at 20:51
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There are two ways of guaranteeing that someone cannot access your system remotely.

  1. As others have already suggested, you will need to reinstall the system.
  2. Unplug the network (wired and/or WiFi).

Neither is a pleasant option.

  • Thanks for your help! I'm comfortable with reinstalling the system - I've just installed Xubuntu on a new-to-me laptop - but just didn't want to go to the trouble if there was something in system settings or some kind of command line jingo that would reset to a default for remote access. – user311397 Sep 18 '18 at 17:58
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If a person that you do not trust (no matter who this may be) has or has had administrator rights on the system, you may treat this as a compromised system.

A compromised system "does not belong to you", as in "you don't know what may be running on it or what changes has been made to it". You should reinstall the machine from scratch, making sure to first back up any personal documents beforehand. For maximum paranoia, you could avoid backing up personal binary executables (recompile these later after checking the source code) and personal scripts (read them first).

Ordinarily, one would not recommend backing up files from a compromised system, but instead to rebuild the system and then restore the most recent known untainted backup of personal files etc., but in this case this may not be possible or feasible.

When setting up the new system, you obviously would use new passwords, especially for root, and you would not set up accounts with authorized_keys files (for SSH) with old keys.

  • Thanks for your help! I'm comfortable with reinstalling the system - I've just installed Xubuntu on a new-to-me laptop - but just didn't want to go to the trouble if there was something in system settings or some kind of command line jingo that would reset to a default for remote access. I appreciate the pointers about keys & passwords. – user311397 Sep 18 '18 at 17:59
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No, unfortunately there is not a blanket setting for "do not allow anyone to access remotely this computer".

You could disable ssh, set up the firewall etc. but the only way you can be sure to eliminate all backdoors and remote accesses is to reinstall the whole system.

  • Thanks for your help! I'm comfortable with reinstalling the system - I've just installed Xubuntu on a new-to-me laptop - but just didn't want to go to the trouble if there was something in system settings or some kind of command line jingo that would reset to a default for remote access. – user311397 Sep 18 '18 at 17:59

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