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Are processes within screen treated differently from foreground processes?



The 2019 Stack Overflow Developer Survey Results Are InHow can I see what processes are running?How do you detach the 2nd screen from within another screen?How are the processes in UNIX numbered?UNIX- Identify which processes are running more that 6hoursWhy there are two sequential screen processes?Send commands to screen within screenLeft and right square brackets treated differently by sed/bashWhy kernel threads are treated as processesWhat is background and Foreground processes in JobsReplace screen process from within screen



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0















Assume I have a long running process, long_running_proc with a single TCP connection to host host.example.com.



Is that process treated differently, by the OS or the shell, when it's run as a foreground process vs background or behind screen?



For instance:



~ long_running_proc --connect host.example.com
...


vs.



~ screen
~ long_running_proc --connect host.example.com
[ctrl-a] + d
~


vs.



~ long_running_proc --connect host.example.com &
[1] 67539
~


Are there different rules to process interruptions or context switches? Do they have a lower priority? Would I be more likely to get a TCP timeout with a screened/background process?










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    0















    Assume I have a long running process, long_running_proc with a single TCP connection to host host.example.com.



    Is that process treated differently, by the OS or the shell, when it's run as a foreground process vs background or behind screen?



    For instance:



    ~ long_running_proc --connect host.example.com
    ...


    vs.



    ~ screen
    ~ long_running_proc --connect host.example.com
    [ctrl-a] + d
    ~


    vs.



    ~ long_running_proc --connect host.example.com &
    [1] 67539
    ~


    Are there different rules to process interruptions or context switches? Do they have a lower priority? Would I be more likely to get a TCP timeout with a screened/background process?










    share|improve this question







    New contributor




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






















      0












      0








      0








      Assume I have a long running process, long_running_proc with a single TCP connection to host host.example.com.



      Is that process treated differently, by the OS or the shell, when it's run as a foreground process vs background or behind screen?



      For instance:



      ~ long_running_proc --connect host.example.com
      ...


      vs.



      ~ screen
      ~ long_running_proc --connect host.example.com
      [ctrl-a] + d
      ~


      vs.



      ~ long_running_proc --connect host.example.com &
      [1] 67539
      ~


      Are there different rules to process interruptions or context switches? Do they have a lower priority? Would I be more likely to get a TCP timeout with a screened/background process?










      share|improve this question







      New contributor




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












      Assume I have a long running process, long_running_proc with a single TCP connection to host host.example.com.



      Is that process treated differently, by the OS or the shell, when it's run as a foreground process vs background or behind screen?



      For instance:



      ~ long_running_proc --connect host.example.com
      ...


      vs.



      ~ screen
      ~ long_running_proc --connect host.example.com
      [ctrl-a] + d
      ~


      vs.



      ~ long_running_proc --connect host.example.com &
      [1] 67539
      ~


      Are there different rules to process interruptions or context switches? Do they have a lower priority? Would I be more likely to get a TCP timeout with a screened/background process?







      shell process gnu-screen background-process process-management






      share|improve this question







      New contributor




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











      share|improve this question







      New contributor




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









      share|improve this question




      share|improve this question






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      asked 2 days ago









      JonLucaJonLuca

      1034




      1034




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      New contributor





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






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      Check out our Code of Conduct.




















          1 Answer
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          active

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          2














          In general, by default the only difference is that it would receive a SIGTTIN (or SIGTTOU) signal if it tried to read (or write) the tty while being in the background.



          Other differences as to priorities or higher context switches depend on your shell (or screen) if it willingly does anything of that sort, such as changing the process’s “nice” number or maybe binding it to one particular CPU and if that CPU happens to be interrupted a lot. Normally shells don't do anything of this sort unless requested.



          Higher probability of getting TCP timeouts might be related to whether your process does get stopped by one of the above signals (due to attempted tty access), in which case it wouldn’t have any chance to receive and therefore reply to network traffic.



          If you think of it, daemon processes are the most “background” processes possible, and they certainly aren’t second-class processes.



          I can’t be exact about specifically screen’s detach operation but its documentation says that detached processes continue running, and that screen detaches itself from the process's tty, so the process goes on basically with no difference as to normal foreground or background operation. You would have difficulties at giving it commands, though, being your interactive terminal detached from the process's virtual terminal. This might not be good for your process if at some point it expects input from its terminal.






          share|improve this answer

























          • This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

            – JonLuca
            2 days ago






          • 1





            I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

            – Torin
            2 days ago











          • @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

            – LL3
            2 days ago












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          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          2














          In general, by default the only difference is that it would receive a SIGTTIN (or SIGTTOU) signal if it tried to read (or write) the tty while being in the background.



          Other differences as to priorities or higher context switches depend on your shell (or screen) if it willingly does anything of that sort, such as changing the process’s “nice” number or maybe binding it to one particular CPU and if that CPU happens to be interrupted a lot. Normally shells don't do anything of this sort unless requested.



          Higher probability of getting TCP timeouts might be related to whether your process does get stopped by one of the above signals (due to attempted tty access), in which case it wouldn’t have any chance to receive and therefore reply to network traffic.



          If you think of it, daemon processes are the most “background” processes possible, and they certainly aren’t second-class processes.



          I can’t be exact about specifically screen’s detach operation but its documentation says that detached processes continue running, and that screen detaches itself from the process's tty, so the process goes on basically with no difference as to normal foreground or background operation. You would have difficulties at giving it commands, though, being your interactive terminal detached from the process's virtual terminal. This might not be good for your process if at some point it expects input from its terminal.






          share|improve this answer

























          • This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

            – JonLuca
            2 days ago






          • 1





            I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

            – Torin
            2 days ago











          • @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

            – LL3
            2 days ago
















          2














          In general, by default the only difference is that it would receive a SIGTTIN (or SIGTTOU) signal if it tried to read (or write) the tty while being in the background.



          Other differences as to priorities or higher context switches depend on your shell (or screen) if it willingly does anything of that sort, such as changing the process’s “nice” number or maybe binding it to one particular CPU and if that CPU happens to be interrupted a lot. Normally shells don't do anything of this sort unless requested.



          Higher probability of getting TCP timeouts might be related to whether your process does get stopped by one of the above signals (due to attempted tty access), in which case it wouldn’t have any chance to receive and therefore reply to network traffic.



          If you think of it, daemon processes are the most “background” processes possible, and they certainly aren’t second-class processes.



          I can’t be exact about specifically screen’s detach operation but its documentation says that detached processes continue running, and that screen detaches itself from the process's tty, so the process goes on basically with no difference as to normal foreground or background operation. You would have difficulties at giving it commands, though, being your interactive terminal detached from the process's virtual terminal. This might not be good for your process if at some point it expects input from its terminal.






          share|improve this answer

























          • This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

            – JonLuca
            2 days ago






          • 1





            I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

            – Torin
            2 days ago











          • @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

            – LL3
            2 days ago














          2












          2








          2







          In general, by default the only difference is that it would receive a SIGTTIN (or SIGTTOU) signal if it tried to read (or write) the tty while being in the background.



          Other differences as to priorities or higher context switches depend on your shell (or screen) if it willingly does anything of that sort, such as changing the process’s “nice” number or maybe binding it to one particular CPU and if that CPU happens to be interrupted a lot. Normally shells don't do anything of this sort unless requested.



          Higher probability of getting TCP timeouts might be related to whether your process does get stopped by one of the above signals (due to attempted tty access), in which case it wouldn’t have any chance to receive and therefore reply to network traffic.



          If you think of it, daemon processes are the most “background” processes possible, and they certainly aren’t second-class processes.



          I can’t be exact about specifically screen’s detach operation but its documentation says that detached processes continue running, and that screen detaches itself from the process's tty, so the process goes on basically with no difference as to normal foreground or background operation. You would have difficulties at giving it commands, though, being your interactive terminal detached from the process's virtual terminal. This might not be good for your process if at some point it expects input from its terminal.






          share|improve this answer















          In general, by default the only difference is that it would receive a SIGTTIN (or SIGTTOU) signal if it tried to read (or write) the tty while being in the background.



          Other differences as to priorities or higher context switches depend on your shell (or screen) if it willingly does anything of that sort, such as changing the process’s “nice” number or maybe binding it to one particular CPU and if that CPU happens to be interrupted a lot. Normally shells don't do anything of this sort unless requested.



          Higher probability of getting TCP timeouts might be related to whether your process does get stopped by one of the above signals (due to attempted tty access), in which case it wouldn’t have any chance to receive and therefore reply to network traffic.



          If you think of it, daemon processes are the most “background” processes possible, and they certainly aren’t second-class processes.



          I can’t be exact about specifically screen’s detach operation but its documentation says that detached processes continue running, and that screen detaches itself from the process's tty, so the process goes on basically with no difference as to normal foreground or background operation. You would have difficulties at giving it commands, though, being your interactive terminal detached from the process's virtual terminal. This might not be good for your process if at some point it expects input from its terminal.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited 2 days ago

























          answered 2 days ago









          LL3LL3

          1,2099




          1,2099












          • This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

            – JonLuca
            2 days ago






          • 1





            I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

            – Torin
            2 days ago











          • @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

            – LL3
            2 days ago


















          • This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

            – JonLuca
            2 days ago






          • 1





            I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

            – Torin
            2 days ago











          • @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

            – LL3
            2 days ago

















          This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

          – JonLuca
          2 days ago





          This is exactly what I was wondering. Thanks for the detailed response! I suppose it'll become somewhat process dependent at that point.

          – JonLuca
          2 days ago




          1




          1





          I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

          – Torin
          2 days ago





          I believe in the case of screen a pseudo tty is used. When screen is detached the tty still exists and is still the controlling terminal of the process executed in screen.

          – Torin
          2 days ago













          @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

          – LL3
          2 days ago






          @Torin @JonLuca True, thank you. I never use screen and had misunderstood its docs: I thought screen detaches the process but in fact it detaches itself from the process’s pty, so yes the process is still fully connected and controlled by that pty. Answer updated.

          – LL3
          2 days ago











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