The "UP (restart required)" state explains that the node is currently up, however, the configuration was changed and a reboot of the node is required for the change to take affect.
An example of some configuration changes that can trigger the "restart required" flag.
- Kernel version has changed. (Category or device level)
- Kernel parameters have changed. (Category or device level)
- Network configuration has changed (new interface was added, existing interface modified on a node.
- The software image of a node was changed. (Category or device level)