The Cisco iOS is a single file that a router will load into RAM when it boots up typically from Flash.
In this example,
I've connected to an 1841 router
sow Flash shows us the operating system stored in Flash. Show
version shows us that this is the system file that the router is using.
So the router loaded this image from Flash into RAM and that's the operating system that the router is
currently using.
Now, every operating system has a file system that's used for the organizational files.
An operating system will typically store files in a file system which includes directories and files
within directories. In windows
as an example, you use a backslash to indicate directories.
So as an example, in Windows, you would go to C colon backslash users,
David in my example, desktop to view files on the desktop. Linux uses a forward slash for the directory
structure. On a router
Once again show flash shows us the flash
DIR or DIR also shows us the contents of flash, notice flash colon forward slash.
We also have the make directory option so we could create a directory called Test in Flash.
So now when we use the command DIR we see this directory called test, which is very similar to
what you typically find in Linux.
I could then use the show running command or show running-config command and I could pipe that
and in this case, I could redirect the output to flash
test and then let's push it to a file called showrun.cfg.
So now when I use the command DIR, I see the directory test, that I could use the command DIR
flash test
and we can see the showrun.cfg file stored in that directory.
Notice the show Flash Command not only shows me the root directory but in this case, also shows me
that file in this directory called Test.
So notice DIR versus show Flash.
So if you've used Linux, this is very similar to Linux commands or if you've used CMD in Windows,
it's very similar.
We can read the contents of that file by using the more command, so more flash:/test
/
shrn.cfg and that actually reads the contents of the file in that directory.
So the Cisco iOS provides a feature called the Cisco iOS Integrated File System, or Cisco IFS.
This system allows you to create, navigate and manipulate directories on a Cisco device.
The directories that are available are dependent on the platform that you're using,
file systems that you'll come across include flash memory file contents
as I've demonstrated, you also have network file systems such as TFTP or Trivial File Transfer Protocol,
RCP or Remote Copy and File Transfer Protocol or FTP.
You also have other places where you can write data such as NVRAM, so a Cisco device could have
a USB flash,
It could have flash memory on the motherboard,
it could have RAM, NVRAM and FTP.