Changes

We can depict the following approaches to on the field upgrading, depending on the system capabilities and operating environments:

* With the help of the U-Boot commands (tftpload, protect, erase and cp) we can download and store kernel images, file system images and U-Boot itself in the target system.

* Due to the previous considerations, automatic upgrade procedures are hard to implement.

* System running Linux can be updated from user space using '''standard applications and tools'''. Most of the times the upgrade procedures can be created using common shell commands and scripts.

* Please note that, in order to erase and write MTD flash partitions, their writability flag must be set in Linux. '''Usually the MTD partition dedicated to u-boot is protected against write in Linux''', so an update of the kernel is required before storing a new u-boot image. Updating U-Boot is not a common operation during the system lifetime, but sometimes it is required to solve some bugs or implement new features.

When the system doesn't allow a remote access, an operator must locally access the system through its user interface (in the best case) or through the serial port (in the worst case). If the

When the system features a LAN or internet connection, a remote-update strategy can be implemented. If the machine can be contacted (for example using a telnet or ssh connection), it is quite simple to activate a script that executes all the necessary commands to complete the upgrade procedure.