I have located and backed up the original mali.ko file and copied the new version to my sdcard. However when I try to replace the original file with the new one, ES File Explorer will not do it. I've also tried Terminal Emulator with the following results: # su # cp -i /sdcard/mali.ko /system/lib/modules cp: overwrite '/system/lib/modules/mali.ko'? y cp: can't create '/system/lib/modules/mali.ko' : File exists # su # cat /sdcard/mali.ko > /system/lib/modules/mali.ko cannot create /system/lib/modules/mali.ko: read-only file system My tablet is rooted with Z4Root. Superuser shows the Terminal Emulator in its list of rooted apps, but not File Explorer. I'm by no means an expert on this so I'm maybe missing something obvious. Can anyone please advise what? Edit: OK now solved. /system is read-only and needs to be temporarily changed to read-write. Easily done using Root Explorer.