From where does sysctl -a print all kernel parameters?

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We have a Linux machine (Redhat 6)



When we print all parameters from /etc/sysctl.conf we see only ~20
but when we perform sysctl -a we see more than 200.



So from where sysctl -a print all these parameters ?



Or for example when we do



sysctl -w variable=value


how to know where the variable should be saved?



How to know each parameters if it is dynamic or static?










share|improve this question



























    up vote
    3
    down vote

    favorite












    We have a Linux machine (Redhat 6)



    When we print all parameters from /etc/sysctl.conf we see only ~20
    but when we perform sysctl -a we see more than 200.



    So from where sysctl -a print all these parameters ?



    Or for example when we do



    sysctl -w variable=value


    how to know where the variable should be saved?



    How to know each parameters if it is dynamic or static?










    share|improve this question

























      up vote
      3
      down vote

      favorite









      up vote
      3
      down vote

      favorite











      We have a Linux machine (Redhat 6)



      When we print all parameters from /etc/sysctl.conf we see only ~20
      but when we perform sysctl -a we see more than 200.



      So from where sysctl -a print all these parameters ?



      Or for example when we do



      sysctl -w variable=value


      how to know where the variable should be saved?



      How to know each parameters if it is dynamic or static?










      share|improve this question















      We have a Linux machine (Redhat 6)



      When we print all parameters from /etc/sysctl.conf we see only ~20
      but when we perform sysctl -a we see more than 200.



      So from where sysctl -a print all these parameters ?



      Or for example when we do



      sysctl -w variable=value


      how to know where the variable should be saved?



      How to know each parameters if it is dynamic or static?







      linux sysctl






      share|improve this question















      share|improve this question













      share|improve this question




      share|improve this question








      edited Apr 4 '17 at 23:00









      Gilles

      512k12010141545




      512k12010141545










      asked Apr 4 '17 at 6:54









      yael

      65221330




      65221330




















          2 Answers
          2






          active

          oldest

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          up vote
          2
          down vote













          Sysctl settings are stored in the kernel. These settings influence kernel behavior; basically, they're variables of the kernel which programs running on the system can read and write.



          When the kernel boots, each sysctl setting has a default value. This value can be changed at any time by a program such as the sysctl command, or, under Linux, by writing to the corresponding file under /proc/sys.



          The file /etc/sysctl.conf does not determine the value of the settings at run time. It's only used at boot time, to change some settings from the default value compiled into the kernel. If you've made some changes to /etc/sysctl.conf, you can apply them as a whole by restarting the sysctl “service” — the sysctl service doesn't correspond to a running process, it's a pseudo-service that just loads the settings into the kernel when it starts.



          If you want to change a setting so that the value is preserved across reboots, add it to /etc/sysctl.conf. To apply a setting temporarily or to try it out, use sysctl or echo … >/proc/sys/….






          share|improve this answer



























            up vote
            0
            down vote














            How to know each parameter if it is dynamic or static?




            All the kernel parameters in sysctl are dynamic. When you check the number depending on your kernel version sysctl -a | wc -l it should be more than 1000.



            To read the values you have several smart options:



            sysctl net.ipv4.ip_forward # display specific parameter
            sysctl net.ipv4 # display all net.ipv4.* parameters
            sysctl -a # display all parameters


            And to write the values persistently you can use /etc/sysctl.conf or any conf file inside /etc/sysctl.d/ directory, and once you update the conf file you need to reload the configuration file.



            sysctl -p [filename]


            Of course, you can just restart the the sysctl “service” as Gilles outlined.




            From where does sysctl -a print all kernel parameters?




            From the pseudo file system procfs (man procfs). It provides an interface to kernel data structures. It is commonly mounted at /proc automatically by the system.






            share|improve this answer






















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              2 Answers
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              2 Answers
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              up vote
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              Sysctl settings are stored in the kernel. These settings influence kernel behavior; basically, they're variables of the kernel which programs running on the system can read and write.



              When the kernel boots, each sysctl setting has a default value. This value can be changed at any time by a program such as the sysctl command, or, under Linux, by writing to the corresponding file under /proc/sys.



              The file /etc/sysctl.conf does not determine the value of the settings at run time. It's only used at boot time, to change some settings from the default value compiled into the kernel. If you've made some changes to /etc/sysctl.conf, you can apply them as a whole by restarting the sysctl “service” — the sysctl service doesn't correspond to a running process, it's a pseudo-service that just loads the settings into the kernel when it starts.



              If you want to change a setting so that the value is preserved across reboots, add it to /etc/sysctl.conf. To apply a setting temporarily or to try it out, use sysctl or echo … >/proc/sys/….






              share|improve this answer
























                up vote
                2
                down vote













                Sysctl settings are stored in the kernel. These settings influence kernel behavior; basically, they're variables of the kernel which programs running on the system can read and write.



                When the kernel boots, each sysctl setting has a default value. This value can be changed at any time by a program such as the sysctl command, or, under Linux, by writing to the corresponding file under /proc/sys.



                The file /etc/sysctl.conf does not determine the value of the settings at run time. It's only used at boot time, to change some settings from the default value compiled into the kernel. If you've made some changes to /etc/sysctl.conf, you can apply them as a whole by restarting the sysctl “service” — the sysctl service doesn't correspond to a running process, it's a pseudo-service that just loads the settings into the kernel when it starts.



                If you want to change a setting so that the value is preserved across reboots, add it to /etc/sysctl.conf. To apply a setting temporarily or to try it out, use sysctl or echo … >/proc/sys/….






                share|improve this answer






















                  up vote
                  2
                  down vote










                  up vote
                  2
                  down vote









                  Sysctl settings are stored in the kernel. These settings influence kernel behavior; basically, they're variables of the kernel which programs running on the system can read and write.



                  When the kernel boots, each sysctl setting has a default value. This value can be changed at any time by a program such as the sysctl command, or, under Linux, by writing to the corresponding file under /proc/sys.



                  The file /etc/sysctl.conf does not determine the value of the settings at run time. It's only used at boot time, to change some settings from the default value compiled into the kernel. If you've made some changes to /etc/sysctl.conf, you can apply them as a whole by restarting the sysctl “service” — the sysctl service doesn't correspond to a running process, it's a pseudo-service that just loads the settings into the kernel when it starts.



                  If you want to change a setting so that the value is preserved across reboots, add it to /etc/sysctl.conf. To apply a setting temporarily or to try it out, use sysctl or echo … >/proc/sys/….






                  share|improve this answer












                  Sysctl settings are stored in the kernel. These settings influence kernel behavior; basically, they're variables of the kernel which programs running on the system can read and write.



                  When the kernel boots, each sysctl setting has a default value. This value can be changed at any time by a program such as the sysctl command, or, under Linux, by writing to the corresponding file under /proc/sys.



                  The file /etc/sysctl.conf does not determine the value of the settings at run time. It's only used at boot time, to change some settings from the default value compiled into the kernel. If you've made some changes to /etc/sysctl.conf, you can apply them as a whole by restarting the sysctl “service” — the sysctl service doesn't correspond to a running process, it's a pseudo-service that just loads the settings into the kernel when it starts.



                  If you want to change a setting so that the value is preserved across reboots, add it to /etc/sysctl.conf. To apply a setting temporarily or to try it out, use sysctl or echo … >/proc/sys/….







                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered Apr 5 '17 at 1:41









                  Gilles

                  512k12010141545




                  512k12010141545






















                      up vote
                      0
                      down vote














                      How to know each parameter if it is dynamic or static?




                      All the kernel parameters in sysctl are dynamic. When you check the number depending on your kernel version sysctl -a | wc -l it should be more than 1000.



                      To read the values you have several smart options:



                      sysctl net.ipv4.ip_forward # display specific parameter
                      sysctl net.ipv4 # display all net.ipv4.* parameters
                      sysctl -a # display all parameters


                      And to write the values persistently you can use /etc/sysctl.conf or any conf file inside /etc/sysctl.d/ directory, and once you update the conf file you need to reload the configuration file.



                      sysctl -p [filename]


                      Of course, you can just restart the the sysctl “service” as Gilles outlined.




                      From where does sysctl -a print all kernel parameters?




                      From the pseudo file system procfs (man procfs). It provides an interface to kernel data structures. It is commonly mounted at /proc automatically by the system.






                      share|improve this answer


























                        up vote
                        0
                        down vote














                        How to know each parameter if it is dynamic or static?




                        All the kernel parameters in sysctl are dynamic. When you check the number depending on your kernel version sysctl -a | wc -l it should be more than 1000.



                        To read the values you have several smart options:



                        sysctl net.ipv4.ip_forward # display specific parameter
                        sysctl net.ipv4 # display all net.ipv4.* parameters
                        sysctl -a # display all parameters


                        And to write the values persistently you can use /etc/sysctl.conf or any conf file inside /etc/sysctl.d/ directory, and once you update the conf file you need to reload the configuration file.



                        sysctl -p [filename]


                        Of course, you can just restart the the sysctl “service” as Gilles outlined.




                        From where does sysctl -a print all kernel parameters?




                        From the pseudo file system procfs (man procfs). It provides an interface to kernel data structures. It is commonly mounted at /proc automatically by the system.






                        share|improve this answer
























                          up vote
                          0
                          down vote










                          up vote
                          0
                          down vote










                          How to know each parameter if it is dynamic or static?




                          All the kernel parameters in sysctl are dynamic. When you check the number depending on your kernel version sysctl -a | wc -l it should be more than 1000.



                          To read the values you have several smart options:



                          sysctl net.ipv4.ip_forward # display specific parameter
                          sysctl net.ipv4 # display all net.ipv4.* parameters
                          sysctl -a # display all parameters


                          And to write the values persistently you can use /etc/sysctl.conf or any conf file inside /etc/sysctl.d/ directory, and once you update the conf file you need to reload the configuration file.



                          sysctl -p [filename]


                          Of course, you can just restart the the sysctl “service” as Gilles outlined.




                          From where does sysctl -a print all kernel parameters?




                          From the pseudo file system procfs (man procfs). It provides an interface to kernel data structures. It is commonly mounted at /proc automatically by the system.






                          share|improve this answer















                          How to know each parameter if it is dynamic or static?




                          All the kernel parameters in sysctl are dynamic. When you check the number depending on your kernel version sysctl -a | wc -l it should be more than 1000.



                          To read the values you have several smart options:



                          sysctl net.ipv4.ip_forward # display specific parameter
                          sysctl net.ipv4 # display all net.ipv4.* parameters
                          sysctl -a # display all parameters


                          And to write the values persistently you can use /etc/sysctl.conf or any conf file inside /etc/sysctl.d/ directory, and once you update the conf file you need to reload the configuration file.



                          sysctl -p [filename]


                          Of course, you can just restart the the sysctl “service” as Gilles outlined.




                          From where does sysctl -a print all kernel parameters?




                          From the pseudo file system procfs (man procfs). It provides an interface to kernel data structures. It is commonly mounted at /proc automatically by the system.







                          share|improve this answer














                          share|improve this answer



                          share|improve this answer








                          edited Sep 17 at 8:25

























                          answered Sep 16 at 18:16









                          prosti

                          215114




                          215114



























                               

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