Read the kernel log on a VPS with dmesg
A process vanished with no error of its own. Find the OOM kill in dmesg and journalctl -k, and read the disk and network messages a guest kernel sends.
#journalctl
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Systemd unit won't start: read the exit code
Read systemctl status before anything else. What 203/EXEC and 226/NAMESPACE mean, and why a unit can start cleanly and exit one second later.