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A prompt to erase Flash occurs when issuing the copy running-config startup-config command

Core Issue

Issuing the copy running-config startup-config command may produce a prompt to erase Flash, as shown in this command output: 

Router#copy run start
Destination filename [start]?
Erase flash: before copying? [confirm]
Erasing the flash filesystem will remove all files! Continue? [confirm]

 Erasing device...
 ee ...erasedee
 Erase of flash: complete
 Verifying checksum...  OK (0xA83F)
 7056 bytes copied in 0.836 secs

To erase any files on the Flash device, including the Cisco IOS  Software file, select Enter at the Erase flash: before copying? [confirm] prompt. The router then reloads and goes into ROM Monitor (ROMmon) mode.


To resolve this issue, enter n so that the Cisco IOS Software file in Flash is not erased. The running configuration file is copied into Flash, but the Cisco IOS Software file also remains on Flash, leaving the router bootable.

As a workaround, issue the write memory command. This saves the running configuration to NVRAM, as this command never prompts to erase Flash.

If Flash has already been erased, do not reload the router because it will go into ROMmon mode, since no Cisco IOS Software image is present on Flash.

Copy the Cisco IOS Software file back into Flash before reloading the router.

For instructions on this procedure, refer to Loading Software using TFTP or RCP.

When Problem Occurs

After software configuration change

Version history
Revision #:
1 of 1
Last update:
‎06-18-2009 03:53 PM
Updated by:
New Member

So true, but it still would still be much better to be able to turn this off.  For a variety of reasons, my admin group generally saves a copy of the config to the flash.  I burn myself on this "feature" every three years or so because 99% my routers don't try to do this. And, when one actually does try to Erase on Save, I may have thought it just wanted me to confirm the save and then ran through the prompts.  My fault of course. But that's the pace we keep most days.  Just better to be able to turn it off and then erase/squeeze/reformat when I want and need too.  I litterally manage hundres of routers on a semi-routine basis.  I guess I've been lucky to have only blown up something important with feature only once.

Cisco Employee

The reason why this happen is related more on the formatting on the compact Flash.

Class B file system asks for the format prompt and the class C does not.


In the follwing link explains how to proceed to get the desired formating:

I hope it helps.