According to the
getconf man page:
NAME getconf — get configuration values SYNOPSIS getconf [−v specification] system_var ... DESCRIPTION In the first synopsis form, the getconf utility shall write to the standard output the value of the vari‐ able specified by the system_var operand. ... OPERANDS The following operands shall be supported: ... system_var A name of a configuration variable. All of the following variables shall be supported: * The names in the Variable column of the table in the DESCRIPTION of the sysconf() function in the System Interfaces volume of POSIX.1‐2008... * The names of the symbolic constants used as the name argument of the confstr() function in the System Interfaces volume of POSIX.1‐2008... * The names of the symbolic constants listed under the headings ``Maximum Values'' and ``Mini‐ mum Values'' in the description of the <limits.h> header in the Base Definitions volume of POSIX.1‐2008... The implementation may add other local values.
How does an implementation add other local variables? Is there an
/etc/ configuration file, or does it come from the environment somehow?