Operating System Features and Services

The Cisco IOS File System (IFS) has different directories, depending on the device. The IFS also allows the creation of subdirectories in flash memory or on a disk. The figure below displays the output of the show file system command, which lists all of the available file systems on the router.

📂 File System Entries Explained

Prefix	Description	Type	Access Flags	Notes
flash:	Primary flash memory (internal storage)	disk	rw	Stores IOS image, configurations, and other essential files
nvram:	Non-volatile RAM	nvram	rw	Stores the startup-config file that loads during boot
system:	System-internal virtual file system	opaque	rw	Used internally by the IOS; users typically don’t interact directly
tmpsys:	Temporary system file system	opaque	ro	Read-only virtual file system used during runtime operations
null:	Bit bucket file system	opaque	rw	Used to discard unwanted output, similar to /dev/null in Linux
usbflash0:	USB storage device (if connected)	disk	rw	Useful for backups, software updates, and config transfers
tar:	Used for accessing or creating .tar archive files	opaque	rw	Enables file packaging, commonly for IOS bundles
ftp:	File Transfer Protocol	opaque	rw	Enables file access via remote FTP servers
scp:	Secure Copy Protocol	opaque	rw	Secure file transfers using SSH
tftp:	Trivial File Transfer Protocol	opaque	rw	Lightweight file transfers, commonly used during IOS upgrades

🛠️ Key Concepts:

• Type describes the nature of the file system: disk (physical/virtual), nvram, or opaque (special-purpose).
• Flags such as rw Indicate Read/Write access.
• Some file systems like null:, system:, and tmpsys: are mostly internal-use and rarely accessed directly by administrators.

The Flash File System

The figure below displays the output of the dir command. Since Flash is the default file system, the dir command lists the contents of Flash.

📌 Explanation of Key Files:

Filename	Purpose
c1900-universalk9-...bin	Cisco IOS operating system binary image
config.txt	Backup of the router’s configuration (startup or running)
vlan.dat	Stores VLAN configuration info (used by switches and integrated interfaces)
sigdef-category.xml.sgn	Signature definition file, often used in security contexts
private-config.text	Holds encrypted private configuration data
multiple-fs-objects.tar	Archived bundle file containing multiple configuration or system objects

The NVRAM File System

To view and list the contents of NVRAM, the command will be given as dir NVRAM: in user exec mode, as shown in the Figure below.

Description of Files in nvram::

Filename	Purpose
startup-config	The configuration the router uses on boot. It’s loaded into running-config.
underlying-config	May store fallback or base-level configuration (platform-dependent).
private-config	Contains encrypted passwords or private keys not visible in startup-config.

Switch File Systems

The show file systems command also shows the file systems on a Catalyst switch, which are the same as on a Cisco router, as shown in the figure.

📘 Key Details:

Prefix	Description
flash:	Internal flash memory—stores IOS image and system files
nvram:	Non-volatile memory—used for startup-config
null:	Discards outputs (like a digital void)
usbflash0:	External USB (if connected)
tar:	Enables handling of .tar archive files
ftp:	Used for file transfers via FTP protocol
tftp:	Used for TFTP file transfers, often during upgrades
xmodem:/ymodem:	Serial-based file transfer protocols (rare, mostly fallback)

💡 You’ll notice switches, like routers, share many file system prefixes, though their internal flash size may vary depending on the model.

Backup and Restoring using Text files

Backup

Using Tera Term, we can also back up the Configuration file and restore the configuration from the text file when needed. The steps for backup and restoring using Tera Term is the following:-

1. On the File menu of Tera Term, click Log.
2. Then select the location where you want to save the file. Now Tera Term will start capturing.
3. Once the capture has been started, execute the show running-config or show startup-config command at the privileged EXEC prompt. The displayed text in the Tera Terminal will be directed to the chosen file.
4. After completing the capture, select Close in the Tera Term: Log window.
5. View the file at the chosen location to verify that it was not corrupted.

Restoring

When configuration is copied from a text file and pasted into a terminal window, the Inter Operating System executes each line of the text file as a command. So, the captured file will require editing to ensure that encrypted passwords are in plain text and that there is no non-command text.

Furthermore, the device must be set to the global configuration mode to receive the commands from the text file pasted into the terminal window. The following are the steps to restore the configuration using Tera Term.

1. On the File menu of Tera Term, click Send File.
2. Locate the configuration text file to be copied into the device and click Open.
3. Tera Term will paste the file into the device, and the text will be applied as a command.

Backup and Restoring Configurations with TFTP

Backup

Startup configuration or running configuration files can be stored on a TFTP (Trivial File Transfer Protocol) server and restored in the event of a problem. The configuration file should also be included in the network documentation.

To save the running configuration or the startup configuration file to a TFTP (Trivial File Transfer Protocol) server, use the copy running-config tftp or copy startup-config tftp command. Following are the steps to back up the running configuration to a TFTP server:

1. Enter the copy running-config tftp command in user exec mode and then enter the hostname or IP address where the configuration file will be stored.
2. Enter the name to assign to the configuration file.
3. Press Enter to confirm every choice.

The figure below illustrates the backup process to TFTP.

Restoring

To restore the running configuration or the startup configuration from a TFTP (Trivial File Transfer Protocol) server, use copy tftp running-config or copy tftp startup-config command. Following are the steps to restore the running configuration from a TFTP server:

1. Enter the copy tftp running-config command in user exec mode then enter the hostname or IP address where the configuration file is stored.
2. Enter the name to assign to the configuration file.

The Figure below illustrates the restore process from the TFTP server.

Backing Up and Restoring Using a USB

Backup

Before backing up to a USB port, it is important to verify that the USB drive is there and confirm the name of the drive using the show file systems command in the user exec mode. If the USB drive is there, use the copy run usbflash0:/ command to copy the configuration file to the USB flash drive. Be sure to use the name of the flash drive exactly, as indicated in the file system.

The slash indicates the root directory of the USB flash drive. Then the IOS will prompt for the filename. If the file is already copied and exists on the USB flash drive, the router will then prompt to overwrite. We can see files and directories in the USB using the dir command.

Restore

To copy the file back, use the command copy usbflash0:/Router-Config running-config to restore a running configuration where Router-Config is the backup file name in the USB.

Conclusion

Mastering the Cisco IOS File System is essential for CCNA and CCNP students to effectively manage router and switch configurations. This guide has explored key file systems like flash and NVRAM, provided detailed backup and restore methods using TFTP and USB, and offered troubleshooting tips. By applying these practices, network engineers can ensure system reliability and prepare for real-world challenges. Continuous learning and hands-on practice with commands like show file systems and copy running-config tftp will solidify your expertise.