Debugging DHCP using tcpdump

Debugging DHCP using tcpdump

With lot of time spent home during stay-at-home order active in my area I decided it’s a time to overhaul my home network setup.

I think I’ll get into details in the following posts but at this time I want to tell about an issue with DHCP leases I was able to track down using tcpdump.

Moved to Hugo

Moved to Hugo

Hey-hey kids it has been a while, right? Ok, I’m planning to blow the dust off this blog.

Don’t expect anything grandiose yet but I did some homework and moved the blog from Octopress to Hugo so this tin lizzy has a heart of a fighter jet now.

See you soon.

Mt. Shasta in one day 2018/07/01

Mt. Shasta in one day 2018/07/01

As you have noticed I continue to trail off the paved path of the technically inclined blog and venture into hiking/mountaineering Internet backcountry. The reason is I’m an extremely lazy guy who promised to get back to Shasta almost a year ago. It’s time to be back as promised!

Mt. Whitney in one day 2018/06/09

Mt. Whitney in one day 2018/06/09

Why this post in this blog? - I am generally trying to keep this blog technically inclined. Researching information on one day mt. Whitney hike I was able to find bits of useful information here and there but no ‘end-to-end product’ so to say. This post is an attempt to decrease amount of googling you need to do. Plus doing this hike in one day wasn’t a cakewalk so quite naturally I need to brag a bit, please bear with me.

Disclaimer - use the information as well as anything you find on the Internet as a baseline. Mountaineering is an inherently dangerous activity. Be prepared, be cautious and be lucky. No book or Internet publication is able to provide you with a hands on experience.

Ubuntu user hits thread number limit preventing SSH login

Ubuntu user hits thread number limit preventing SSH login

Recently I was investigating quite an interesting issue - there is Ubuntu based VM our testers run some tests on. It was reported they’re unable to log into the virtual machine.

After a brief investigation it became clear the issue is not network or SSH key related.

These are records from auth log:

/var/log/auth.log

Feb 28 20:21:39 test-instance sshd[21954]: pam_unix(sshd:session): session opened for user ubuntu by (uid=0)
Feb 28 20:21:39 test-instance systemd-logind[756]: New session 75 of user ubuntu.
Feb 28 20:21:39 test-instance sshd[21954]: fatal: fork of unprivileged child failed
Feb 28 20:21:39 test-instance systemd-logind[756]: Removed session 75.

Quite an obscure error message, but smells like cgroup problem. Indeed: