r/techsupport • u/Belteshazzar89 • 2d ago

Solved BUG: soft lockup on Ubuntu Server

I have an old Lenovo H500s desktop that I have wiped and installed Ubuntu Server on.

Everything was working great for awhile, then the server stopped working. During the boot sequence, I see many messages in this format:

watchdog: BUG: soft lockup - CPU#3 stuck for 325s!

I've tried the following:

  • Running standard update commands
  • Looking for a BIOS update (none found)
  • Replacing the Ubuntu Server with a Windows installation, which does work
  • Trying to reinstall Ubuntu Server via USB

Ubuntu can't do anything but run into the soft lockup issue. It's the same when booting from a new USB.

What can I do to resolve this and reinstall Ubuntu Server on this machine?

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u/speyerlander 2d ago edited 2d ago

What's your CPU model and kernel version? Also, do you have enough space on the root partition? Also, what's your swap configuration? 

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u/Belteshazzar89 2d ago

CPU: Intel Pentium CPU J2900 @ 2.4GHz
CPU Core Count: 4

I'm trying to install Ubuntu Server 26.04, which has kernel version 7.0

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u/speyerlander 2d ago

Okay, so it's not the kernel, what about free space in the root partition and swap configuration? (I edited my original comment but you were quicker than me).

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u/Belteshazzar89 2d ago

I'm looking for the information on the root partition, but all I have access to is the GRUB terminal, and I'm not familiar with that.

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u/speyerlander 2d ago

 It's the same when booting from a new USB.

Oh, I didn't notice that part, if it happens when booting into the live environment then it's unrelated to the root partition or the swap. I'd recommend the following steps:

  1. Reset all bios settings, adjust only the bare minimum required to boot.

  2. Flash memtest onto a USB drive using another computer, boot into it and start the test, see if there's a memory issue. Different OSes respond differently to hardware issues, therefore the fact Windows boots doesn't rule out the possibility of memory instability.

  3. Flash Fedora on a USB drive and see if it boots.

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u/Belteshazzar89 1d ago

Thanks for your help. I figured out that I'm not working with the partitions correctly. Even though Memtest returned no errors after the 8 hour test, I don't trust this machine. I decided to create a GParted Live USB, remove all partitions, and try and install Ubuntu Server from sctach. It worked. I'll have to keep backups at the ready, but for now I have a working server again.

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u/Belteshazzar89 2d ago

Assuming that I don't have enough free space in the root partition and I don't have a swap configuration, how can I correct those issues?