A systemd service will not start. How do you investigate?

Question

Accepted Answer

I start with systemctl status, which gives me the failed state, the exit code, and the last 10 log lines. The exit code alone often tells the story, a 203 means the ExecStart binary was not found or is not executable, while a plain 1 usually means the app itself started and then died. Then journalctl -u for the service, with -n 100 and --no-pager, gives me the full error, and that normally says exactly why it stopped. Next I read the unit itself with systemctl cat, checking the ExecStart path, the User it runs as, the WorkingDirectory, and any After or Requires dependencies, because the cause is very often a wrong absolute path, a missing environment variable, or a permissions problem, like the service user not being able to read a file or bind to a port below 1024. If it is still unclear, I run the ExecStart command by hand as that service user, which strips systemd out of the picture and shows me the raw error. And after any edit to the unit file I run daemon-reload before restarting, because otherwise systemd is still running the old definition, and that is the step people forget most.

Answer

The service starts then immediately exits and systemd keeps restarting it. What do you check?

A crash loop: journalctl shows the repeated error; check the exit code, Restart= policy, and whether a dependency (DB, mount, network) is not ready, you may need After=/Requires= or a readiness wait.

Answer

How do you make a service start on boot? systemctl enable <svc> (creates the boot symlink); enable --now both enables and starts it. status shows "enabled" vs "disabled".

A systemd service will not start. How do you investigate?

A systemd service will not start. How do you investigate?

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