Saving grub.conf file
 

Question:
1. How can I save existing grub.conf file and install newest kernel/patch update in my redhat server
2. How to observe the changes on grub.conf file
3. How to chose old kernel.

Thanks in advance.

1. Make a copy of it someplace else before running an update. Generally, one uses yum to update software (including the kernel) on a Red Hat system.
2. Run a diff between the old and new copy of the grub.conf file.
3. Select it from the GRUB bootloader menu. Note that yum purges old kernels (keeping just the most recent and second most recent, so these are the only choices you will have). You can also modify the default entry in the grub.conf.

Note that Red Hat provides extensive documentation for their OSes; you probably want to read it.

Actually, the limit is controlled by
in /etc/yum.conf.

Generally you would just set that to the reqd num and probably not bother backing up grub.conf in this case, unless you were going to manually edit it.

Of course you should backup your whole system regularly anyway.