Hello All, I am trying IOCTL example provided in http://linux.die.net/lkmpg/x892.html, both user-space and kernel space using same chardev.h file for IOCTL number. But the number receiving in kernel is different than number in kernel. I printed both the received number and defined number in dmesg, please find it below. // IOCTL number which is in kernel [ 6417.807403] Value of IOCTL_GET_NTH_BYTE: -1073454078 [ 6417.807398] Value of IOCTL_GET_MSG: -2147195903 [ 6417.807391] Value of IOCTL_SET_MSG: -2147195904 // IOCTL number which is received by kernel. [ 6426.691360] Passed IOCTL:number 0 [ 6426.691464] Passed IOCTL:number -1074930088 [ 6426.691537] Passed IOCTL:number 134514878 Can you please tell why this number is getting changed while receiving in kernel ? // Here is the definition of numbers. #define MAJOR_NUM 100 #define IOCTL_SET_MSG _IOR(MAJOR_NUM, 0, char *) #define IOCTL_GET_MSG _IOR(MAJOR_NUM, 1, char *) #define IOCTL_GET_NTH_BYTE _IOWR(MAJOR_NUM, 2, int) -- Regards Jeshwanth Kumar N K +91-7411483498