The default value is $HOME/config/environment
The file should contain lines of the form
VAR=valueNo evaluation of the line constants is performed, so having a line of the form.
BIGFILE=$HOME/bigfilewill result in the value of BIGFILE being $HOME/bigfile and not what might be expected (expansion of $HOME into the home directory).
The file can also contain comments, which are denoted by a # character at the beginning of the line.