Do I need to restart server after a linux kernel update?
There are at least two reasons for rebooting:
- You probably want to use the advantages of the newer version (security fixes)
- Usually during a kernel update the module tree of the old kernel is removed. Thus if you (or some script) unload a module then the system cannot load it again because it finds only the newer one on disk (if at all) and this is compiled for a different kernel and thus cannot be loaded (at least usually).
To actually use the new kernel you will have to reboot.
No way around that.
Do you have to reboot immediately after installing the update ?
In general NOT, you can schedule the reboot for a more convenient moment.
But it is NOT a good idea to install more updates before you reboot.
Some updates have different versions depending on which kernel you are running.
And anyway: After rebooting with a new kernel always check for updates. Some of your existing packages may need a new version after the kernel update.
Ksplice takes care of all security updates but it depends on the updates and it's not free. You can check here for details for yum as well.
You also have the option of using kexec which will require a reboot but will skip the hardware part of the boot.