Have search all around, couldn't find any valid answers so I decided to ask myself.
So I was just making a rom, which I have already installed. It's based on Cataclysm (personal use only - Till I ask for perm).
I have installed the rom, then I decided to theme some system files. And so I did. I theme the "Settings.apk" for now, and decided to push it to my device instead of installing the whole rom over again. Now mind you when I made roms and modified system apps, pushing these files to the device was straight forward. However on this Hammerhead, I've been running into some issues.
When pushing the file to my device like this
adb push Settings.apk system/priv-app
I get an error that says -
failed to copy "Settings.apk" to "system/priv-app/Settings.apk" : Read only file system.
[x] adb root - Permission Denied [x] adb remount - Permission Denied
[x] adb shell [x] $ su - gave it permission [x] $ mount -o rw,remount /system - It mounts it.
Device not found.
Thanks to everyone that answered my question in detail.