boot system flash [filename]
Specifies the IOS image file on flash memory to load at next system boot, overriding the default boot sequence.
boot system flash [filename]When to Use This Command
- Upgrading to a new IOS version by pointing to the new image file
- Rolling back to a previous stable IOS version after a failed upgrade
- Booting from a backup image when the primary image is corrupted
- Selecting a specific IOS image for testing or compatibility requirements
Command Examples
Specify a single IOS image to boot
boot system flash c2960-lanbasek9-mz.150-2.SE11.binThis command sets the router/switch to load the specified IOS image from flash on next boot. No immediate output is shown; the configuration is stored in running-config.
Configure multiple fallback boot images
boot system flash c2960-lanbasek9-mz.150-2.SE11.bin
boot system flash c2960-lanbasek9-mz.122-55.SE12.binMultiple boot system commands can be entered. The device tries the first image; if it fails, it attempts the next. This provides redundancy.
Understanding the Output
This command does not produce immediate output. To verify the boot configuration, use 'show running-config | include boot system' or 'show boot'. The 'show boot' output displays the current boot path, the image to boot, and whether the configuration is saved. A valid configuration shows the expected filename; missing or incorrect filenames will cause boot failure.
CCNA Exam Tips
Remember that 'boot system flash' overrides the default boot sequence; if the specified file is missing, the device may not boot.
The command is entered in global configuration mode; changes take effect after 'copy running-config startup-config' and reload.
CCNA may test the difference between 'boot system flash' (specific file) and 'boot system flash' without filename (first valid image).
Know that multiple 'boot system' commands create a fallback list; order matters.
Common Mistakes
Typing the filename incorrectly (case-sensitive on some platforms) causing boot failure.
Forgetting to save the configuration with 'copy running-config startup-config' before reload.
Using 'boot system flash' without a filename when intending to specify a particular image.
Related Commands
reload
The reload command reboots a Cisco IOS device, typically used to apply configuration changes or recover from a system issue.
show boot
Displays the current boot settings, including the boot system commands and the startup configuration file location, used to verify or troubleshoot the router's boot process.
show running-config
Displays the current active configuration in DRAM, showing all non-default settings.
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