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I have a linux server running with apache, and with gammu to send sms. The gammu works fine if I send sms using shell command. My problem is: I have a php file and I need send sms using gammu, but I receive an error when I try: $phone=28739847398; shell_exec('gammu sendsms TEXT '.$phone.' -text "Halooo .."'); I receive this error: Error opening device, it doesn't exist. If I try it: shell_exec('sudo gammu sendsms TEXT '.$phone.' -text "Halooo .."'); I receive nothing