Recovering from a System Crash Cisco

 The boot loader provides access into the switch if the operating system cannot be used because of missing or damaged system files. The boot loader has a command-line that provides access to the files stored in flash memory.

The boot loader can be accessed through a console connection following these steps:

Step 1. Connect a PC by console cable to the switch console port. Configure terminal emulation software to connect to the switch.
Step 2. Unplug the switch power cord.
Step 3. Reconnect the power cord to the switch and, within 15 seconds, press and hold down the Mode button while the System LED is still flashing green.
Step 4. Continue pressing the Mode button until the System LED turns briefly amber and then solid green; then release the Mode button.
Step 5. The boot loader switch: prompt appears in the terminal emulation software on the PC.

Type the help or ? at the boot loader prompt to view a list of available commands.

By default, the switch attempts to automatically boot up by using information in the BOOT environment variable. To view the path of the switch BOOT environment variable type the set command. Then, initialize the flash file system using the flash_init command to view the current files in flash, as shown in the output.

switch: set
BOOT=flash:/c2960-lanbasek9-mz.122-55.SE7/c2960-lanbasek9-mz.122-55.SE7.bin
(output omitted)
switch: flash_init
Initializing Flash...
flashfs[0]: 2 files, 1 directories
flashfs[0]: 0 orphaned files, 0 orphaned directories
flashfs[0]: Total bytes: 32514048
flashfs[0]: Bytes used: 11838464
flashfs[0]: Bytes available: 20675584
flashfs[0]: flashfs fsck took 10 seconds.
...done Initializing Flash.

After flash has finished initializing you can enter the dir flash: command to view the directories and files in flash, as shown in the output.

switch: dir flash: 
Directory of flash:/
    2  -rwx  11834846                 c2960-lanbasek9-mz.150-2.SE8.bin
    3  -rwx  2072                     multiple-fs

Enter the BOOT=flash command to change the BOOT environment variable path the switch uses to load the new IOS in flash. To verify the new BOOT environment variable path, issue the set command again. Finally, to load the new IOS type the boot command without any arguments, as shown in the output.

switch: BOOT=flash:c2960-lanbasek9-mz.150-2.SE8.bin
switch: set
BOOT=flash:c2960-lanbasek9-mz.150-2.SE8.bin
(output omitted)
switch: boot

The boot loader commands support initializing flash, formatting flash, installing a new IOS, changing the BOOT environment variable and recovery of lost or forgotten passwords.