FX30 custom kernel

Dear,
I recently bought two FX30. I tried to build a custom image to add libraries to the initial one. The build success but I can’t flash it on the FX30. I haven’t any problem to flash the rootfs but when I tried to flash the kernel, the kernel’s part seem staying empty : the FX30 reboot in bootloader mode.

user@ES1494VMUBUNTU:~/yocto/build_bin/tmp/deploy/images/swi-mdm9x15$ sudo fastboot devices
[sudo] password for user:
MDM9615    fastboot
user@ES1494VMUBUNTU:~/yocto/build_bin/tmp/deploy/images/swi-mdm9x15$ sudo fastboot erase kernel
erasing 'kernel'...
OKAY [  0.082s]
finished. total time: 0.082s
user@ES1494VMUBUNTU:~/yocto/build_bin/tmp/deploy/images/swi-mdm9x15$ sudo fastboot erase rootfs
erasing 'rootfs'...
OKAY [  0.245s]
finished. total time: 0.245s
user@ES1494VMUBUNTU:~/yocto/build_bin/tmp/deploy/images/swi-mdm9x15$ sudo fastboot flash kernel kernel
sending 'kernel' (3920 KB)...
OKAY [  0.657s]
writing 'kernel'...
OKAY [  0.651s]
finished. total time: 1.309s
user@ES1494VMUBUNTU:~/yocto/build_bin/tmp/deploy/images/swi-mdm9x15$ sudo fastboot flash rootfs rootfs
sending 'rootfs' (26496 KB)...
OKAY [  4.498s]
writing 'rootfs'...
OKAY [  4.081s]
finished. total time: 8.579s
user@ES1494VMUBUNTU:~/yocto/build_bin/tmp/deploy/images/swi-mdm9x15$ sudo fastboot reboot
rebooting...

finished. total time: 0.004s

I managed to boot on my custom kernel by executing the command : “fastboot boot kernel”, the kernel is written in RAM and the FX30 boot correctly but the next reboot will be in bootloader mode. How can I flash the custom kernel definitively ?
Best regards,
Bonnevie Jean

Hello,

May I ask you how you managed to get fastboot working with the FX30 ?
Though my FX30 is properly listed as USB device “Bus 001 Device 038: ID 1199:68c0 Sierra Wireless, Inc.” I am not able to see it neither with “adb devices -l” nor with “fastboot devices -l”.

Thank you in advance for any advice,
Best regards,
Gautier.