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The CIOS stands for Cisco Internetworking Operating System. It is the CLI to many Cisco brand router(s). It is very similar in structure to MS-DOS and Linux, as well as other router operating systems.

Command prompt[?] output:

  • User Mode: Router>
  • Priveledged Exec Mode: Router#

command format:

Commands are single words. Arguments are interpreted when a space seperates the argument from the command. Cisco calls arguments subcommands[?]. Command-line arguments may contain dashes.

  • Example: show running-config. (shows the active configuration.)


Unlike most operating systems, the CIOS has so few commands that it will interpret truncated commands without requiring the user to autocomplete the command. Entering a command that requires an argument without an argument will produce:

%Incomplete Command.

To display arguments use the "?" argument. ("?" is also the help command.)

Command History[?]

Like most operating systems, the CIOS has a command history[?]. It can be accessed using the up and down arrow keys (like other operating systems.)


Commands will not be shown to users that or do not have sufficient privilege[?] to access them. Commands will fail to execute as if they don't exist. The highest priveledge mode for a user is the "Priveleged Exec" mode. (accessible using the Enable command).

Administrators should also be familiar with the following modes:

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