If a disabled function is called in a script, it will return awarning E_WARNING, the script does not stop executing.
Parameter disable_functions allows you to disable only internal functions PHP, it does not affect user-defined functions. With its help, for example, you can prevent site scripts from sending mail using the function mail or block the ability to use functions like exec and shell_exec.
To disable the function, do the following:
To resume the disabled functions, delete them from the list, re-save the settings and wait for the changes to take effect.