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Access a Cisco device in ROMMON-mode

Cisco 2960 switch

From IOS

Bypass the normal boot process and enter ROMMON mode directly upon the next reboot.

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Switch#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
Switch(config)#boot manual 
Switch(config)#end
Switch#reload

System configuration has been modified. Save? [yes/no]: no      <----- if asked
Proceed with reload? [confirm]                                  <----- press <Enter>

We're in ROMMON-mode.

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Boot Sector Filesystem (bs) installed, fsid: 2
Base ethernet MAC Address: bc:f1:f2:59:06:00
Xmodem file system is available.
The password-recovery mechanism is enabled.
Initializing Flash...
flashfs[0]: 4 files, 3 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 65544192
flashfs[0]: Bytes used: 16104448
flashfs[0]: Bytes available: 49439744
flashfs[0]: flashfs fsck took 19 seconds.
...done Initializing Flash.
done.

The system is not configured to boot automatically.  The
following command will finish loading the operating system
software:

    boot


switch:

Missing or corrupt IOS

Let's simulate a non-working IOS by "accidently" erasing the flash filesystem. Restart the switch afterwards.

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Switch#erase flash:
Erasing the flash filesystem will remove all files! Continue? [confirm]
flashfs[2]: 0 files, 1 directories
flashfs[2]: 0 orphaned files, 0 orphaned directories
flashfs[2]: Total bytes: 65544192
flashfs[2]: Bytes used: 1024
flashfs[2]: Bytes available: 65543168
flashfs[2]: flashfs fsck took 25 seconds.
Erase of flash: complete
Switch#
Switch#reload

System configuration has been modified. Save? [yes/no]: no          <----- if asked
Proceed with reload? [confirm]                                      <----- press <Enter>

The BOOT environment variable is still set to boot c2960-lanbasek9-mz.152-7.E7.bin but it's not there. The switch will not be able to boot and will enter ROMMON-mode automatically.

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Welcome to minicom 2.8

OPTIONS: I18n 
Port /dev/ttyUSB0, 09:36:24

Press CTRL-A Z for help on special keys


Boot Sector Filesystem (bs) installed, fsid: 2
Base ethernet MAC Address: 6c:41:0e:18:0b:00
Xmodem file system is available.
The password-recovery mechanism is enabled.
Initializing Flash...
flashfs[0]: 1 files, 1 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 65544192
flashfs[0]: Bytes used: 3584
flashfs[0]: Bytes available: 65540608
flashfs[0]: flashfs fsck took 18 seconds.
...done Initializing Flash.
done.
Loading "flash:/c2960-lanbasek9-mz.152-7.E7.bin"...flash:/c2960-lanbasek9-mz.152-7.E7.bin: no such file or directory

Error loading "flash:/c2960-lanbasek9-mz.152-7.E7.bin"

Interrupt within 5 seconds to abort boot process.
Boot process failed...

The system is unable to boot automatically.  The BOOT
environment variable needs to be set to a bootable
image.


switch:

Cold start

First disconnect the power cable from the switch. Minicom gives no output yet.

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Welcome to minicom 2.8

OPTIONS: I18n 
Port /dev/ttyUSB0, 13:50:27

Press CTRL-A Z for help on special keys

<blinking_cursor>

Now reconnect the power cable. The switch boots and while doing the POST, the SYST LED blinks green. This takes about X seconds. After POST, the blinking LED changes pattern. Press the Mode button once. The switch does not initialize Flash and enters ROMMON-mode.

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Welcome to minicom 2.8

OPTIONS: I18n 
Port /dev/ttyUSB0, 09:44:08

Press CTRL-A Z for help on special keys


Boot Sector Filesystem (bs) installed, fsid: 2
Base ethernet MAC Address: 6c:41:0e:18:0b:00
Xmodem file system is available.
The password-recovery mechanism is enabled.
Initializing Flash...
flashfs[0]: filesystem check interrupted!
...done Initializing Flash.

The system has been interrupted, or encountered an error
during initialization of the flash filesystem.  The following
commands will initialize the flash filesystem, and finish
loading the operating system software:

    flash_init
    boot


switch:

Cisco 1941 router