# 基本语法
systemctl [OPTIONS] COMMAND [UNIT...]

# 启动服务
systemctl start nginx.service

# 停止服务
systemctl stop nginx.service

# 重启服务（先 stop 再 start）
systemctl restart nginx.service

# 重新加载配置（不中断服务，要求服务支持 reload）
systemctl reload nginx.service

# 先 reload，如果不支持则 restart
systemctl reload-or-restart nginx.service

# 同上，但尝试 reload 失败时也 restart
systemctl try-reload-or-restart nginx.service

# 查看服务详细状态
systemctl status nginx.service

# 设置开机自启
systemctl enable nginx.service

# 取消开机自启
systemctl disable nginx.service

# 启用并立即启动
systemctl enable --now nginx.service

# 禁用并立即停止
systemctl disable --now nginx.service

# 查看 enable 创建的符号链接
systemctl enable nginx.service 2>&1

# 查看符号链接
ls -la /etc/systemd/system/multi-user.target.wants/

# 查看所有 Unit 文件的启用状态
systemctl list-unit-files

# 过滤特定状态
systemctl list-unit-files --state=enabled
systemctl list-unit-files --state=disabled
systemctl list-unit-files --state=masked

# 查看特定 Unit
systemctl is-enabled nginx.service

# 列出所有已加载的 Unit
systemctl list-units

# 只列出 service 类型
systemctl list-units --type=service

# 列出所有（包括未加载的）
systemctl list-units --all

# 列出 Unit 文件
systemctl list-unit-files --type=service

# 按状态过滤
systemctl list-units --state=failed

# 显示所有失败的服务
systemctl --failed

# 查看正向依赖（启动时需要什么）
systemctl list-dependencies nginx.service

# 查看反向依赖（谁依赖此服务）
systemctl list-dependencies nginx.service --reverse

# 只显示当前 active 的
systemctl list-dependencies nginx.service --state=active

# 显示所有层级
systemctl list-dependencies nginx.service --all

# 显示指定 Target 的依赖树
systemctl list-dependencies multi-user.target

# 屏蔽服务（完全禁止启动，比 disable 更强）
systemctl mask nginx.service

# 取消屏蔽
systemctl unmask nginx.service

# 查看被 mask 的符号链接
ls -la /etc/systemd/system/nginx.service
# 输出：nginx.service -> /dev/null

# 查看所有失败的服务
systemctl --failed

# 查看特定服务的失败详情
systemctl status myapp.service

# 查看服务日志
journalctl -u myapp.service -n 50

# 重置失败状态
systemctl reset-failed myapp.service

# 重置所有失败状态
systemctl reset-failed

# 1. 查看状态和最近日志
systemctl status myapp.service

# 2. 查看详细日志
journalctl -u myapp.service --since "10 minutes ago"

# 3. 检查 Unit 文件语法
systemd-analyze verify /etc/systemd/system/myapp.service

# 4. 检查安全限制
systemd-analyze security myapp.service

# 5. 尝试手动启动以捕获错误
sudo -u myappuser /usr/local/bin/myapp

# 6. 修复后重置状态并重启
systemctl reset-failed myapp.service
systemctl restart myapp.service

# 同时操作多个服务
systemctl start nginx.service php-fpm.service redis.service

# 启用多个服务
systemctl enable nginx.service php-fpm.service

# 重启多个服务
systemctl restart nginx php-fpm redis

# 使用通配符（systemctl 支持 glob 模式）
systemctl status 'web*'

# 重启某个 Slice 下的所有服务
systemctl restart user-1000.slice

#!/bin/bash
# restart-all-webapp.sh — 重启所有 web 相关服务

services=(
    nginx.service
    php8.2-fpm.service
    redis-server.service
    myapp-worker.service
)

for svc in "${services[@]}"; do
    echo "Restarting ${svc}..."
    if systemctl restart "${svc}"; then
        echo "  ✓ ${svc} restarted successfully"
    else
        echo "  ✗ ${svc} failed to restart"
    fi
done

# 检查是否有失败的服务
failed=$(systemctl --failed --no-legend | wc -l)
if [ "$failed" -gt 0 ]; then
    echo "⚠ ${failed} service(s) in failed state"
    systemctl --failed --no-pager
fi

# 对于支持 reload 的服务（如 Nginx），零停机更新配置
systemctl reload nginx.service

# 对于支持 graceful restart 的服务
# ExecReload=/bin/kill -HUP $MAINPID
systemctl reload myapp.service

# 确保关键服务在崩溃后自动重启
# 在 Unit 文件中配置：
# [Service]
# Restart=on-failure
# RestartSec=5
# StartLimitBurst=3
# StartLimitIntervalSec=60

# 手动触发重启（例如部署新版本后）
systemctl restart myapp.service

# 验证服务正在运行
systemctl is-active myapp.service && echo "OK" || echo "FAIL"

#!/bin/bash
# maintenance.sh — 进入维护模式

echo "进入维护模式..."
systemctl stop nginx.service
systemctl mask nginx.service  # 防止被意外启动

# 执行维护操作...
echo "维护中... 按 Enter 继续"
read

# 退出维护模式
echo "退出维护模式..."
systemctl unmask nginx.service
systemctl start nginx.service
echo "服务已恢复"