https://www.xbcatm.com/zh/tags/maintenance/基于 HTTP、DNS、TLS、Caddy、SSH、发布与恢复的可复现运维现场笔记。Hugozh-CNhttps://www.xbcatm.com/zh/notes/a-maintenance-timer-should-leave-its-last-result-visible/Sun, 23 Aug 2026 00:00:00 +0000https://www.xbcatm.com/zh/notes/a-maintenance-timer-should-leave-its-last-result-visible/用一个 oneshot 服务、一个定时器、有界运行时间与日志证据搭配使用。<p>cron 式语法并不是维护任务契约的全部。命令需要一个清晰的服务身份、一个有界的运行时间，以及能区分&quot;未调度&quot;与&quot;运行但失败&quot;的证据。一个 systemd 定时器与 oneshot 服务能把这些关注点分开。</p> <h2 id="把工作定义成服务">把工作定义成服务</h2> <p>使用显式用户与绝对命令路径：</p> <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-ini" data-lang="ini"><span class="line"><span class="cl"><span class="c1"># /etc/systemd/system/site-check.service</span> </span></span><span class="line"><span class="cl"><span class="k">[Unit]</span> </span></span><span class="line"><span class="cl"><span class="na">Description</span><span class="o">=</span><span class="s">Read-only public site check</span> </span></span><span class="line"><span class="cl"> </span></span><span class="line"><span class="cl"><span class="k">[Service]</span> </span></span><span class="line"><span class="cl"><span class="na">Type</span><span class="o">=</span><span class="s">oneshot</span> </span></span><span class="line"><span class="cl"><span class="na">User</span><span class="o">=</span><span class="s">sitecheck</span> </span></span><span class="line"><span class="cl"><span class="na">ExecStart</span><span class="o">=</span><span class="s">/usr/local/bin/check-public-site</span> </span></span><span class="line"><span class="cl"><span class="na">TimeoutStartSec</span><span class="o">=</span><span class="s">2min</span> </span></span></code></pre></div><p><code>TimeoutStartSec</code> 防止网络或子进程等待无限占用调度。当契约失败时，helper 应返回非零退出码，并且不得修改它所检查的服务。</p> <h2 id="调度该服务">调度该服务</h2> <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-ini" data-lang="ini"><span class="line"><span class="cl"><span class="c1"># /etc/systemd/system/site-check.timer</span> </span></span><span class="line"><span class="cl"><span class="k">[Unit]</span> </span></span><span class="line"><span class="cl"><span class="na">Description</span><span class="o">=</span><span class="s">每小时运行公共站点检查</span> </span></span><span class="line"><span class="cl"> </span></span><span class="line"><span class="cl"><span class="k">[Timer]</span> </span></span><span class="line"><span class="cl"><span class="na">OnCalendar</span><span class="o">=</span><span class="s">hourly</span> </span></span><span class="line"><span class="cl"><span class="na">Persistent</span><span class="o">=</span><span class="s">true</span> </span></span><span class="line"><span class="cl"><span class="na">RandomizedDelaySec</span><span class="o">=</span><span class="s">5min</span> </span></span><span class="line"><span class="cl"><span class="na">Unit</span><span class="o">=</span><span class="s">site-check.service</span> </span></span><span class="line"><span class="cl"> </span></span><span class="line"><span class="cl"><span class="k">[Install]</span> </span></span><span class="line"><span class="cl"><span class="na">WantedBy</span><span class="o">=</span><span class="s">timers.target</span> </span></span></code></pre></div><p><code>Persistent=true</code> 会在机器恢复后补跑错过的日历事件。<code>RandomizedDelaySec</code> 把一个窗口内的例行工作分散开；当任务必须在精确时刻运行时它并不合适。</p> <h2 id="启用前先验证">启用前先验证</h2> <p>检视日历表达式，然后手动启动服务：</p> <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-sh" data-lang="sh"><span class="line"><span class="cl">systemd-analyze calendar hourly </span></span><span class="line"><span class="cl">systemctl start site-check.service </span></span><span class="line"><span class="cl">systemctl status site-check.service </span></span><span class="line"><span class="cl">journalctl -u site-check.service -n <span class="m">50</span> --no-pager </span></span></code></pre></div><p>只有当服务在预期的用户、环境、路径与网络访问下成功时才启用定时器：</p> <div class="highlight"><pre tabindex="0" class="chroma"><code class="language-sh" data-lang="sh"><span class="line"><span class="cl">systemctl <span class="nb">enable</span> --now site-check.timer </span></span><span class="line"><span class="cl">systemctl list-timers site-check.timer </span></span></code></pre></div><h2 id="对服务结果告警">对服务结果告警</h2> <p>定时器触发并不等于成功。要监控 oneshot 服务的退出状态或日志结果。保持 stdout 简洁，调试需要的详细制品写入一个有界的路径。</p> <h2 id="来源">来源</h2> <ul> <li><a href="https://man7.org/linux/man-pages/man5/systemd.timer.5.html">systemd.timer(5)</a>，日历定时器、持久化与延迟行为，已核验 2026-08-23。</li> <li><a href="https://man7.org/linux/man-pages/man7/systemd.time.7.html">systemd.time(7)</a>，日历表达式语法，已核验 2026-08-23。</li> <li><a href="https://www.freedesktop.org/software/systemd/man/latest/systemd.service.html">systemd.service</a>，oneshot 服务语义，已核验 2026-08-23。</li> </ul>