Cisco 3750X – Fixing Boot Loop After Failed IOS Upgrade

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I was trying to upgrade WS-C3750X-48T-S IOS software from universalk9-mz.122-53.SE2.bin to c3750e-universalk9-mz.152-4.E6.bin

First I deleted all files under flash: folder, then downloaded new one from tftp (yes its mistake)

and reload the switch now its booting in loop again and again and giving error

Loading "flash:/c3750e-universalk9-mz.122-53.SE2/c3750e-universalk9-mz.122-53.SE2.bin"...flash:/c3750e-universalk9-mz.122-53.SE2/c3750e-universalk9-mz.122-53.SE2.bin: no such file or directory

Error loading "flash:/c3750e-universalk9-mz.122-53.SE2/c3750e-universalk9-mz.122-53.SE2.bin"

After this I pressed MODE button and powered on the switch, when it comes to switch: prompt, i issued

switch: dir flash:
Directory of flash:/

    2  -rwx  25906176  <date>               c3750e-universalk9-mz.152-4.E6.bin
    3  -rwx  3019      <date>               config.text
    4  -rwx  1938      <date>               private-config.text
    5  -rwx  5144      <date>               multiple-fs

31542784 bytes available (26128896 bytes used)
How can I copy back original IOS back in place?

Best Answer

The boot variable says that the IOS image file should be searched at the following path:

flash:/c3750e-universalk9-mz.122-53.SE2/c3750e-universalk9-mz.122-53.SE2.bin

And as it seems, neither directory flash:/c3750e-universalk9-mz.122-53.SE2/ nor file c3750e-universalk9-mz.122-53.SE2.bin are there any longer.

There is no need to copy the original image back, just manually force the switch into rommon and make it load the new image. Probably, you just need to wait through a boot cycle, and it will present you with a rommon> prompt

  • (if needed), force the switch into rommon with the mode button procedure. (keep the mode button pressed while power-on for ca. 30sec); the procedure is also described in various FAQs related to password recovery of 2960/3560/3750 switches.
  • at the rommon> prompt, type boot flash:/c3750e-universalk9-mz.152-4.E6.bin (because that is the location and filename of the new image uploaded to the switch)
  • once booted up, go into config mode and use the boot system flash flash:/path/file.bin (in your case: boot system flash flash:/c3750e-universalk9-mz.152-4.E6.bin) command, so that it points to the correct IOS image file.

Suggestion: Next time, use the archive download-sw .... commands to upgrade a 3750, especially when upgrading a switch stack. Saves an immeasurable amount of time and avoids most kinds of errors that can happen, even sets the boot system flash ... commands for you.

Hint: it is very possible that when upgrading from IOS 12.2(53)SE2 to 15.2(4)E6, there will be a microcode upgrade to the ASICs. That will be taken care of automatically upon first boot of the new IOS. Depending on the number of ports (12,24,48), this might need enough time for a decent lunch break.

Disclaimer: This of course will only work if the new IOS image file is not corrupted in any way. If that happens to be the case, you may resort to loading an IOS image via network and TFTP, or booting an IOS image from an USB stick might also work (3750X should be young enough to have an USB port and a rommon version capable of accessing USB storage)

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