openssh not working since updating to kernel 5.15

Mike Looijmans

Bumped against similar issues with ssh servers (also dropbear) and the problem turned out to be a "lack of entropy".

It takes the ssh server up to several minutes to initialize on an embedded system, because there's no source of randomness and /dev/random just blocks.

When you connect to such a system with SSH, everything is fine, no errors, but the connection won't show any activity for a long time.

You can speed it up by writing some random strings to /dev/random.

A quick workaround is to just add "haveged" to your image. That creates an entropy source based on CPU characteristics, which is questionable from a security point of view. A secure workaround would be to have an actual hardware random number generator on board somewhere.


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert

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On 13-02-2023 10:02, gcblair via wrote:
We updated our kernel from 4.x to 5.15 and for some reason openssh has stopped working
We see that sshd.socket is running but not sshd@.service <mailto:sshd@.service>
When I run sshd manually I cannot connect
Everything else seems fine - no error messages
The only thing I changed was the kernel version but I cant seem to understand how that could affect something like openssh
This is how I added opnessh:
IMAGE_FEATURES += "ssh-server-openssh package-management tools-debug"
Would apprecaite any help!