I've been using Observium at work to collect and graph SNMP logs for a couple years now. A while back the graphs started showing "Draw Error" instead of the actual graph. I poked at it a bit, but never got it fixed. I wasn't too worried since I want to use the ELK Stack for most of what Observium does in the future. Today, though, a coworker came and asked about Observium. So I decided to poke at it some more.
The issue turned out to be my php.ini configuration. I usually configure disable_functions like this:
disable_functions = apache_child_terminate,apache_setenv,define_syslog_variables,escapeshellarg,escapeshellcmd,eval,exec,fp,fput,ftp_connect,ftp_exec,ftp_get,ftp_login,ftp_nb_fput,ftp_put,ftp_raw,ftp_rawlist,highlight_file,ini_alter,ini_get_all,ini_restore,inject_code,mysql_pconnect,passthru,php_uname,phpAds_remoteInfo,phpAds_XmlRpc,phpAds_xmlrpcDecode,phpAds_xmlrpcEncode,popen,posix_getpwuid,posix_kill,posix_mkfifo,posix_setpgid,posix_setsid,posix_setuid,posix_setuid,posix_uname,proc_close,proc_get_status,proc_nice,proc_open,proc_terminate,shell_exec,system,xmlrpc_entity_decode,pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority
The thing is, Observium needs to use functions like php_uname, shell_exec, escapeshellarg, etc. So I set it to this:
disable_functions = apache_child_terminate,apache_setenv,define_syslog_variables,fp,fput,ftp_connect,ftp_exec,ftp_get,ftp_login,ftp_nb_fput,ftp_put,ftp_raw,ftp_rawlist,highlight_file,ini_alter,ini_get_all,ini_restore,inject_code,mysql_pconnect,passthru,phpAds_remoteInfo,phpAds_XmlRpc,phpAds_xmlrpcDecode,phpAds_xmlrpcEncode,posix_getpwuid,posix_kill,posix_mkfifo,posix_setpgid,posix_setsid,posix_setuid,posix_setuid,posix_uname,system,xmlrpc_entity_decode,pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority
That seems to have fixed it. Though I might have missed a couple functions, so test things a bit if you just copy/paste my code.
The long and the short of it is: if the normal fixes you find via google don't work when your graphs are not displaying, then check your php config and make sure you have not blocked any functions Observium needs.