we have linux machine redhat 6
when we print all paramers from /etc/sysctl.conf we see only ~20 but when we perform sysctl -a we see more then 200
so from where sysctl -a print all these parameters ?
or for example
when we do
sysctl -w variable=value how to know where variable should be saved ?
second
how to know each parameters if this dynamic or static ?
The option -a of sysctl prints all available options as stated in the manual.
-a, --all Display all values currently available. These options come from the built-in or loaded Linux kernel modules. Some if not all modules provide some variables that can be tuned via sysctl. The /etc/sysctl.conf includes the variables that have been changed. Any variable uses its default value when not changed.
Please, note that there are multiple files to load system parameters like files under /etc/sysctl.d/.
If you want to know whether a variable can be changed or not, you can look at the corresponding file under /proc/sys. Some files (variables) are read-only while others can be read and written.
Here is an example of one changeable variable (1st one) and one read-only (second) from /proc/sys/kernel/
-rw-r--r-- 1 root root 0 Apr 4 10:23 shmmax -r--r--r-- 1 root root 0 Apr 4 10:14 version 
site:www.kernel.org/doc/Documentation/ <parameter-name> is often the quickest to find the appropriate manual page. And anything not overruled from the locations explained in man sysctl or manually by an administrator with echo value > /proc/sys/section/module/parameter or similar should be at the default setting