https://blog.yusukeikoma.com/tags/systemd/Recent content in systemd on Ikoma's BlogHugoen-usSat, 03 Oct 2026 18:08:27 +0900https://blog.yusukeikoma.com/posts/replace-running-daemon-without-downtime/Sat, 03 Oct 2026 18:08:27 +0900https://blog.yusukeikoma.com/posts/replace-running-daemon-without-downtime/A runbook for replacing a running daemon without dropping requests, tested on a small TCP server under real systemd. A plain restart refused or reset connections every time; starting the new version beside the old one avoided refusals but still reset a connection in some runs, and a kernel setting made those resets go away; socket activation produced no errors. Also covered: draining in-flight work against TimeoutStopSec, and a release swap that checks the new version and rolls back.https://blog.yusukeikoma.com/posts/systemd-killmode-self-update/Mon, 28 Sep 2026 09:48:47 +0900https://blog.yusukeikoma.com/posts/systemd-killmode-self-update/A daemon that updates itself by starting a helper and restarting its own unit has a trap: the helper starts inside the service’s cgroup, and systemd kills everything in that cgroup on restart. In a throwaway systemd, a setsid’d helper vanished before its last log line, KillMode=process kept it alive but leaked it into the next instance, and systemd-run gave it its own unit. This post shows the evidence, the fix, and what I did not test.