https://semicolony.dev New sections, pages, and features on Semicolony — guides and simulators for understanding how systems actually work. One item per addition, newest first. en Wed, 10 Jun 2026 00:00:00 GMT https://semicolony.dev/errors https://semicolony.dev/errors Wed, 10 Jun 2026 00:00:00 GMT A new section for the strings you paste into a search engine at 2am: CrashLoopBackOff, OOMKilled, ECONNRESET, exit 137 and five friends. Each page walks the same spine — the symptom as you see it, the commands that narrow it down, causes ranked by how often they turn out to be the answer, and a fix per cause. https://semicolony.dev/errors/exit-code-137 https://semicolony.dev/errors/exit-code-137 Wed, 10 Jun 2026 00:00:00 GMT The standout of the new errors set. 137 means SIGKILL, but it never says who sent it — the kernel OOM killer, the cgroup limit, or a supervisor losing patience. This page sorts out which, fast. https://semicolony.dev/errors/crashloopbackoff https://semicolony.dev/errors/crashloopbackoff Wed, 10 Jun 2026 00:00:00 GMT The most-searched Kubernetes status, taken apart properly. The loop is the symptom; the page is about finding what actually crashed, starting with the one command most people skip: logs --previous. https://semicolony.dev/progress https://semicolony.dev/progress Wed, 10 Jun 2026 00:00:00 GMT The site now keeps score for you: what you have read, what is left, section by section. Stored in your browser — no account, nothing leaves your machine. https://semicolony.dev/ https://semicolony.dev/ Wed, 10 Jun 2026 00:00:00 GMT The front page got rebuilt around how people actually use the site: the daily-use surfaces up top, the library below, less ceremony in between. https://semicolony.dev/codex/linux/the-box-is-slow https://semicolony.dev/codex/linux/the-box-is-slow Thu, 28 May 2026 00:00:00 GMT The sixty-second triage for a sluggish machine: which four commands to run first, what each one rules out, and where to go when none of them explain it. https://semicolony.dev/simulators/goroutine-scheduler https://semicolony.dev/simulators/goroutine-scheduler Tue, 19 May 2026 00:00:00 GMT Watch Go’s M:N scheduler at work — Ps with run queues, an idle P stealing half a busy neighbour’s work, and what a blocking syscall does to the picture. https://semicolony.dev/papers/tail-at-scale https://semicolony.dev/papers/tail-at-scale Tue, 12 May 2026 00:00:00 GMT Dean and Barroso on why p99 latency is a fan-out problem, not a server problem — annotated section by section, with the hedged-request trick spelled out. https://semicolony.dev/postmortems/facebook-2021-bgp-withdrawal https://semicolony.dev/postmortems/facebook-2021-bgp-withdrawal Sat, 02 May 2026 00:00:00 GMT The day facebook.com vanished from the internet: a routine maintenance command, a BGP withdrawal, and the lockout that kept the fix out of reach for hours. https://semicolony.dev/codex/kubernetes/internals/kubelet https://semicolony.dev/codex/kubernetes/internals/kubelet Tue, 21 Apr 2026 00:00:00 GMT The agent that actually runs your pods: the sync loop, CRI, probes, and the garbage collection that quietly decides which images survive on a node. https://semicolony.dev/simulators/split-brain https://semicolony.dev/simulators/split-brain Tue, 14 Apr 2026 00:00:00 GMT Cut the network between replicas and watch two leaders emerge — then see how quorum, fencing, and leases each put the genie back in the bottle. https://semicolony.dev/papers/spanner https://semicolony.dev/papers/spanner Fri, 03 Apr 2026 00:00:00 GMT Google’s globally distributed database, read closely: TrueTime, commit-wait, and why owning atomic clocks turns out to be a consistency strategy. https://semicolony.dev/codex/system-design/playbook/object-storage https://semicolony.dev/codex/system-design/playbook/object-storage Tue, 24 Mar 2026 00:00:00 GMT Designing an S3-shaped system from the interview prompt up: metadata vs. data paths, erasure coding, multipart uploads, and where listings get expensive. https://semicolony.dev/postmortems/gitlab-2017-database-incident https://semicolony.dev/postmortems/gitlab-2017-database-incident Tue, 10 Mar 2026 00:00:00 GMT The rm -rf on the wrong replica, and the part everyone forgets: five backup mechanisms, none of which had been producing usable backups.