Our shared and reseller servers are configured to have the following functions disabled as an added layer of security.
Disabled functions: exec,system,passthru,shell_exec,escapeshellarg,escapeshellcmd,proc_close,proc_open,dl,popen,show_source
posix_kill,posix_mkfifo,posix_getpwuid,posix_setpgid,posix_setsid,posix_setuid,posix_setgid,posix_seteuid
posix_setegid,posix_uname