From WeBWorK

General troubleshooting

• Verify that $netpbm_prefix is set correctly in global.conf. The correct value is usually either /usr/bin or /usr/local/bin.
• Make sure that the following Netpbm utilities are installed in the directory given by $netpbm_prefix.
  • giftopnm
  • ppmtopgm
  • pnmtops
  • pnmtopng
  • pngtopnm

Inappropriate ioctl for device

This error is somewhat mysterious, but in at least one case it was caused by the Netpbm tools using shared libraries instead of statically linked libraries. If this case applies to you, you may need to recompile Netpbm and tell it to use statically linked libraries:

Do you want libnetpbm to be statically linked or shared?
static or shared [shared] ==> static