In '127.0.1.1:+xxxxx' What is the plus character for?

The name of the pictureThe name of the pictureThe name of the pictureClash Royale CLAN TAG#URR8PPP











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On my linux filesystem, a symlinks points to 127.0.1.1:+xxxxx.



Why the plus sign? Could there also be a minus? Why not just 127.0.1.1:xxxxx?










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    On my linux filesystem, a symlinks points to 127.0.1.1:+xxxxx.



    Why the plus sign? Could there also be a minus? Why not just 127.0.1.1:xxxxx?










    share|improve this question







    New contributor




    myMethod is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
    Check out our Code of Conduct.





















      up vote
      2
      down vote

      favorite









      up vote
      2
      down vote

      favorite











      On my linux filesystem, a symlinks points to 127.0.1.1:+xxxxx.



      Why the plus sign? Could there also be a minus? Why not just 127.0.1.1:xxxxx?










      share|improve this question







      New contributor




      myMethod is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.











      On my linux filesystem, a symlinks points to 127.0.1.1:+xxxxx.



      Why the plus sign? Could there also be a minus? Why not just 127.0.1.1:xxxxx?







      linux networking symbolic-link ip-address






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      asked 36 mins ago









      myMethod

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          2 Answers
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          Symbolic links which don't point to a file have no generic meaning at all. In this case it might be the process ID, or a port with some special protocol spoken over it, or another identifier. It all depends on what program made it.



          Software which creates these links simply takes advantage of the facts that 1) a symlink's target may be non-existent or even total nonsense; 2) creating a symlink is a single-syscall completely atomic operation (as is reading its target), unlike creating a regular file which takes at least 3 separate system calls.



          Thus symlink creation can be abused as a way of locking (ensuring single instance of a program) even when other mechanisms may be unreliable. The program doesn't need the symlink to actually resolve to a real file: it only cares about whether creating the link succeeds, or whether it fails due to it already existing.






          share|improve this answer




















          • Thank you for the detailed answer.
            – myMethod
            13 mins ago

















          up vote
          4
          down vote













          As far as I know the "+" means that the number after the IP (the "xxxxx") refers to a "process ID" (not a port which usually uses the notation [IP-address]:[portnumber]).






          share|improve this answer




















          • I just checked it. In my case it really does.
            – myMethod
            10 mins ago










          • @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
            – Albin
            9 mins ago











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          2 Answers
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          active

          oldest

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          2 Answers
          2






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes








          up vote
          0
          down vote



          accepted










          Symbolic links which don't point to a file have no generic meaning at all. In this case it might be the process ID, or a port with some special protocol spoken over it, or another identifier. It all depends on what program made it.



          Software which creates these links simply takes advantage of the facts that 1) a symlink's target may be non-existent or even total nonsense; 2) creating a symlink is a single-syscall completely atomic operation (as is reading its target), unlike creating a regular file which takes at least 3 separate system calls.



          Thus symlink creation can be abused as a way of locking (ensuring single instance of a program) even when other mechanisms may be unreliable. The program doesn't need the symlink to actually resolve to a real file: it only cares about whether creating the link succeeds, or whether it fails due to it already existing.






          share|improve this answer




















          • Thank you for the detailed answer.
            – myMethod
            13 mins ago














          up vote
          0
          down vote



          accepted










          Symbolic links which don't point to a file have no generic meaning at all. In this case it might be the process ID, or a port with some special protocol spoken over it, or another identifier. It all depends on what program made it.



          Software which creates these links simply takes advantage of the facts that 1) a symlink's target may be non-existent or even total nonsense; 2) creating a symlink is a single-syscall completely atomic operation (as is reading its target), unlike creating a regular file which takes at least 3 separate system calls.



          Thus symlink creation can be abused as a way of locking (ensuring single instance of a program) even when other mechanisms may be unreliable. The program doesn't need the symlink to actually resolve to a real file: it only cares about whether creating the link succeeds, or whether it fails due to it already existing.






          share|improve this answer




















          • Thank you for the detailed answer.
            – myMethod
            13 mins ago












          up vote
          0
          down vote



          accepted







          up vote
          0
          down vote



          accepted






          Symbolic links which don't point to a file have no generic meaning at all. In this case it might be the process ID, or a port with some special protocol spoken over it, or another identifier. It all depends on what program made it.



          Software which creates these links simply takes advantage of the facts that 1) a symlink's target may be non-existent or even total nonsense; 2) creating a symlink is a single-syscall completely atomic operation (as is reading its target), unlike creating a regular file which takes at least 3 separate system calls.



          Thus symlink creation can be abused as a way of locking (ensuring single instance of a program) even when other mechanisms may be unreliable. The program doesn't need the symlink to actually resolve to a real file: it only cares about whether creating the link succeeds, or whether it fails due to it already existing.






          share|improve this answer












          Symbolic links which don't point to a file have no generic meaning at all. In this case it might be the process ID, or a port with some special protocol spoken over it, or another identifier. It all depends on what program made it.



          Software which creates these links simply takes advantage of the facts that 1) a symlink's target may be non-existent or even total nonsense; 2) creating a symlink is a single-syscall completely atomic operation (as is reading its target), unlike creating a regular file which takes at least 3 separate system calls.



          Thus symlink creation can be abused as a way of locking (ensuring single instance of a program) even when other mechanisms may be unreliable. The program doesn't need the symlink to actually resolve to a real file: it only cares about whether creating the link succeeds, or whether it fails due to it already existing.







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 18 mins ago









          grawity

          220k32449513




          220k32449513











          • Thank you for the detailed answer.
            – myMethod
            13 mins ago
















          • Thank you for the detailed answer.
            – myMethod
            13 mins ago















          Thank you for the detailed answer.
          – myMethod
          13 mins ago




          Thank you for the detailed answer.
          – myMethod
          13 mins ago












          up vote
          4
          down vote













          As far as I know the "+" means that the number after the IP (the "xxxxx") refers to a "process ID" (not a port which usually uses the notation [IP-address]:[portnumber]).






          share|improve this answer




















          • I just checked it. In my case it really does.
            – myMethod
            10 mins ago










          • @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
            – Albin
            9 mins ago















          up vote
          4
          down vote













          As far as I know the "+" means that the number after the IP (the "xxxxx") refers to a "process ID" (not a port which usually uses the notation [IP-address]:[portnumber]).






          share|improve this answer




















          • I just checked it. In my case it really does.
            – myMethod
            10 mins ago










          • @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
            – Albin
            9 mins ago













          up vote
          4
          down vote










          up vote
          4
          down vote









          As far as I know the "+" means that the number after the IP (the "xxxxx") refers to a "process ID" (not a port which usually uses the notation [IP-address]:[portnumber]).






          share|improve this answer












          As far as I know the "+" means that the number after the IP (the "xxxxx") refers to a "process ID" (not a port which usually uses the notation [IP-address]:[portnumber]).







          share|improve this answer












          share|improve this answer



          share|improve this answer










          answered 25 mins ago









          Albin

          1,204621




          1,204621











          • I just checked it. In my case it really does.
            – myMethod
            10 mins ago










          • @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
            – Albin
            9 mins ago

















          • I just checked it. In my case it really does.
            – myMethod
            10 mins ago










          • @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
            – Albin
            9 mins ago
















          I just checked it. In my case it really does.
          – myMethod
          10 mins ago




          I just checked it. In my case it really does.
          – myMethod
          10 mins ago












          @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
          – Albin
          9 mins ago





          @myMethod glad to help, feel free to "accept" my answer, if it answered you're question.
          – Albin
          9 mins ago











          myMethod is a new contributor. Be nice, and check out our Code of Conduct.









           

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