Mastering Embedded Linux Programming - Second Edition

Atomic file updates

Another approach is to have redundant copies of a root filesystem present in multiple directories of a single filesystem and then use the chroot(8) command to choose one of them at boot time. This allows one directory tree to be updated while another is mounted as the root directory. Furthermore, rather than making copies of files that have not changed between versions of the root filesystem, you could use links. That would save a lot of disk spacew2 and reduce the amount of data to be downloaded in an update package. These are the basic ideas behind atomic file update.

The chroot command runs a program in an existing directory. The program sees this directory as its root directory, and so cannot access any files or directories ...