The cross-compilation environment cannot find arm-linux-gcc under the root user problem:

The reason is: the environment variable (cross-compilation path) may be added under the ordinary user, so when the file created under the root user is compiled with arm-linux-gcc, arm-linux-gcc cannot be found.

Solution: Find a terminal: sudo -s

　　　　　　　　　　source ~/.bashrc

　　　　　　　　　　You can recompile again, provided that the cross-compilation path is added in ~/.bachrc.