If I 'adb push' a file to /system/xbin, will it persistent? If I 'adb push' a file to /system/xbin, will it persistent? will it stay until I flash another image?

$ adb push myfile /system/xbin/myfile


Thank you.
Yes. /system is for persistent firmware files and will survive a wipe/reset unless you don't install another firmware (depends on the MOD's installer/installation script: some preserve other files, some do not).