Try whereis php.ini if you don’t know where that file is. It is usually in the /etc folder.
Use ls to list the directory contents of your folders to see if php.ini is in there.
Open it up with vi and go to the line open_basedir and set to Off or false (forgot which noe it is)
Hit escape and type :wq
then restart Apache with httpd -k restart or however you do it. If this is a shared hosting environment there should be a way for you to edit those options.
Find the line where “open_basedir” is listed and change it. Eg. press /, then type open_basedir and press enter. Press i to go into edit mode. Delete the value after open_basedir and put in the value On. Press escape. Press : and type wq and press enter. Now restart the web server, probably by typing apache2ctl restart and pressing enter.