Today I solved another problem that bugged me for a while. Namely, I wanted to run the free flight prediction runs automatically from cron. When I ran it from the commandline or a script, it worked well, but when I tried to run it directly or through the same script from cron, it always failed with the following message : “critical error : basic_string::_S_construct NULL not valid”<\/p>\n
\nI tried everything that came to my mind and that I found on google, but nothing helped.<\/p>\n
Normally, the program would log the progress to stdout. But the redirected log or the email contained nothing than the error message. So, the error must have happened during initialization. Consequently, I looked at the source again, and now I spotted a possible problem.<\/p>\n
In the program I used getenv(“USER”)<\/strong> and getenv(“HOME”)<\/strong> which I assumed would always be valid. I run the command as root user in cron. If I type echo $HOME<\/strong> or echo $USER<\/strong> at the commandline when logged in as root, it shows the proper values. So I added fallbacks to the respective places in the code as well. Btw: You can reach the prediction results at<\/p>\n
\nBut after adding HOME=\/root<\/strong> and USER=root<\/strong> to \/etc\/cron.d\/flightpred it works.<\/p>\n
\nI still don’t understand, why the env vars were not set when running from cron, but I’m glad it works now.<\/p>\n