When you use the delete command it marks the files as deleted but it doesn't permanently delete them, this is done in purpose to allow file recovery
To permanently delete files on a Flash memory device, use the following command from privileged EXEC mode
When you issue the squeeze command, the router copies all valid files to the beginning of Flash memory and erases all files marked "deleted." At this point, you cannot recover "deleted" files, and you can now write to the reclaimed Flash memory space.
Note The squeeze operation can take as long as several minutes because it can involve erasing and rewriting almost an entire Flash memory space.
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