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SystemPrivileged EXEC

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.

Syntax·Privileged EXEC
show boot

When to Use This Command

  • Verify which IOS image the router will load on next reload after configuring a new boot system command.
  • Check if the router is configured to boot from a TFTP server or from flash memory.
  • Troubleshoot a router that fails to boot by confirming the boot path and configuration register setting.
  • Confirm the startup configuration file location when using a remote file system like TFTP or FTP.

Command Examples

Basic show boot output

show boot
BOOT variable = flash0:/c2900-universalk9-mz.SPA.157-3.M8.bin,12;
CONFIG_FILE variable = 
BOOTLDR variable = 
Configuration register is 0x2102

Standby not ready

Current BOOT file is flash0:/c2900-universalk9-mz.SPA.157-3.M8.bin

BOOT variable: lists the IOS image(s) to load, separated by semicolons. Here it points to a single image in flash0. CONFIG_FILE variable: empty means the router uses the default startup-config in NVRAM. BOOTLDR variable: empty means no boot loader image is specified. Configuration register: 0x2102 indicates normal boot from flash, ignoring break, and 9600 baud console. Current BOOT file: the image that will actually be used on next reload.

show boot with TFTP boot system configured

show boot
BOOT variable = tftp://192.168.1.100/c2900-universalk9-mz.SPA.157-3.M8.bin;
CONFIG_FILE variable = tftp://192.168.1.100/startup-config
BOOTLDR variable = 
Configuration register is 0x2102

Standby not ready

Current BOOT file is tftp://192.168.1.100/c2900-universalk9-mz.SPA.157-3.M8.bin

BOOT variable: points to a TFTP server at 192.168.1.100. CONFIG_FILE variable: also points to a remote startup-config file. This indicates the router will attempt to load both the IOS and configuration from the network. If the TFTP server is unreachable, the router may fail to boot.

Understanding the Output

The show boot command output displays the boot parameters that the router will use on the next reload. The 'BOOT variable' line shows the system image file(s) specified with the 'boot system' global configuration command. Multiple images can be listed, separated by semicolons; the router tries them in order. If the variable is empty, the router uses the first valid image in flash. The 'CONFIG_FILE variable' indicates the location of the startup configuration; if empty, the router uses the default 'startup-config' in NVRAM. The 'BOOTLDR variable' is for a boot loader image (rarely used). The 'Configuration register' is a hexadecimal value that controls boot behavior: 0x2102 is normal (boot from flash, ignore break), 0x2142 ignores startup-config (password recovery), 0x2101 boots from ROMmon. The 'Current BOOT file' shows the image that will actually be loaded based on the current settings. In a production network, ensure the BOOT variable points to a valid image and the configuration register is set correctly to avoid boot failures.

CCNA Exam Tips

1.

Remember that the configuration register 0x2102 is the default and most common setting for normal boot.

2.

The 'boot system' command can specify a TFTP server, flash file, or even a USB device; the show boot command confirms which one is configured.

3.

If the BOOT variable is empty, the router boots from the first valid IOS image in flash; this is a common exam scenario.

4.

The CONFIG_FILE variable can point to a remote file; if it's set incorrectly, the router may fail to load its configuration.

Common Mistakes

Confusing the BOOT variable with the current running image; show boot shows what will be used on next reload, not what is currently running.

Forgetting that multiple boot system commands create a list; the order matters and show boot displays them in order.

Assuming an empty CONFIG_FILE variable means no configuration; it actually means the default startup-config in NVRAM is used.

Related Commands

boot system flash [filename]

Specifies the IOS image file on flash memory to load at next system boot, overriding the default boot sequence.

show startup-config

Displays the saved configuration stored in NVRAM that loads on next device boot.

show version

Displays system hardware and software information, including IOS version, uptime, memory, interfaces, and configuration register, used to verify device identity and software compatibility.

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