You can make a File “immutable” or “unalterable” that it cannot be changed or deleted even by root. Note that this works on (ext2/ext3) filesystems AFAIK.
You can accomplish this by making a file “immutable” by using chattr +i filename command
From the man page:

A file with the ‘i’ attribute cannot be modified: it cannot be deleted [...]

To find how many files are opne at any given time you can type this on the terminal: cat /proc/sys/fs/file-nr
I got this number:
6240 ( total allocated file descriptors since boot)
0 ( total free allocated file descriptors)
94297 ( maximum open file descriptors)

Not that you can check the maximum open file by using this [...]

lsof is a command meaning “list open files”, which is used in many Unix-like systems to report a list of all open files and the processes that opened them. We will look at ways to keep tab open sockets and Internet files with lsof.
To have a real-time tab on open sockets type in watch lsof [...]

People commonly overlook the fact that it is not just the desktops and servers that are potentially running unnecessary services—your network devices are also likely doing this. However, here is a list of services you should look for on your network equipment and turn off if you are not actively using them:

Cisco Discovery Protocol (CDP)

TCP [...]