cron
installsforks
How to install cron?
chaterm/terminal-skills/cron
$npx -y skills add chaterm/terminal-skills --skill cron定时任务管理
SKILL.md
| 1 | # 定时任务管理 |
| 2 | |
| 3 | ## 概述 |
| 4 | Cron 定时任务配置、日志监控、故障排查等技能。 |
| 5 | |
| 6 | ## Crontab 基础 |
| 7 | |
| 8 | ### 管理命令 |
| 9 | ```bash |
| 10 | # 编辑当前用户的 crontab |
| 11 | crontab -e |
| 12 | |
| 13 | # 查看当前用户的 crontab |
| 14 | crontab -l |
| 15 | |
| 16 | # 删除当前用户的 crontab |
| 17 | crontab -r |
| 18 | |
| 19 | # 管理其他用户的 crontab（需要 root） |
| 20 | crontab -u username -e |
| 21 | crontab -u username -l |
| 22 | ``` |
| 23 | |
| 24 | ### 时间格式 |
| 25 | ``` |
| 26 | ┌───────────── 分钟 (0-59) |
| 27 | │ ┌───────────── 小时 (0-23) |
| 28 | │ │ ┌───────────── 日 (1-31) |
| 29 | │ │ │ ┌───────────── 月 (1-12) |
| 30 | │ │ │ │ ┌───────────── 星期 (0-7, 0和7都是周日) |
| 31 | │ │ │ │ │ |
| 32 | * * * * * command |
| 33 | ``` |
| 34 | |
| 35 | ### 特殊字符 |
| 36 | ```bash |
| 37 | * # 任意值 |
| 38 | , # 列表 (1,3,5) |
| 39 | - # 范围 (1-5) |
| 40 | / # 步长 (*/5 每5分钟) |
| 41 | |
| 42 | # 示例 |
| 43 | 0 * * * * # 每小时整点 |
| 44 | */15 * * * * # 每15分钟 |
| 45 | 0 9-17 * * * # 9点到17点每小时 |
| 46 | 0 0 * * 1-5 # 工作日零点 |
| 47 | 0 0 1,15 * * # 每月1号和15号零点 |
| 48 | ``` |
| 49 | |
| 50 | ### 特殊时间字符串 |
| 51 | ```bash |
| 52 | @reboot # 系统启动时 |
| 53 | @yearly # 每年 (0 0 1 1 *) |
| 54 | @monthly # 每月 (0 0 1 * *) |
| 55 | @weekly # 每周 (0 0 * * 0) |
| 56 | @daily # 每天 (0 0 * * *) |
| 57 | @hourly # 每小时 (0 * * * *) |
| 58 | ``` |
| 59 | |
| 60 | ## 配置文件 |
| 61 | |
| 62 | ### 用户 crontab |
| 63 | ```bash |
| 64 | # 位置 |
| 65 | /var/spool/cron/crontabs/username # Debian/Ubuntu |
| 66 | /var/spool/cron/username # CentOS/RHEL |
| 67 | |
| 68 | # 格式 |
| 69 | SHELL=/bin/bash |
| 70 | PATH=/usr/local/bin:/usr/bin:/bin |
| 71 | MAILTO=admin@example.com |
| 72 | |
| 73 | # 任务 |
| 74 | 0 2 * * * /usr/local/bin/backup.sh |
| 75 | ``` |
| 76 | |
| 77 | ### 系统 crontab |
| 78 | ```bash |
| 79 | # /etc/crontab |
| 80 | SHELL=/bin/bash |
| 81 | PATH=/sbin:/bin:/usr/sbin:/usr/bin |
| 82 | MAILTO=root |
| 83 | |
| 84 | # 格式：多了用户字段 |
| 85 | # 分 时 日 月 周 用户 命令 |
| 86 | 0 2 * * * root /usr/local/bin/backup.sh |
| 87 | ``` |
| 88 | |
| 89 | ### cron.d 目录 |
| 90 | ```bash |
| 91 | # /etc/cron.d/myapp |
| 92 | SHELL=/bin/bash |
| 93 | PATH=/usr/local/bin:/usr/bin:/bin |
| 94 | |
| 95 | 0 * * * * appuser /opt/myapp/hourly-task.sh |
| 96 | 0 2 * * * root /opt/myapp/daily-backup.sh |
| 97 | ``` |
| 98 | |
| 99 | ### 预定义目录 |
| 100 | ```bash |
| 101 | /etc/cron.hourly/ # 每小时执行 |
| 102 | /etc/cron.daily/ # 每天执行 |
| 103 | /etc/cron.weekly/ # 每周执行 |
| 104 | /etc/cron.monthly/ # 每月执行 |
| 105 | |
| 106 | # 放入可执行脚本即可 |
| 107 | chmod +x /etc/cron.daily/myscript |
| 108 | ``` |
| 109 | |
| 110 | ## 最佳实践 |
| 111 | |
| 112 | ### 脚本模板 |
| 113 | ```bash |
| 114 | #!/bin/bash |
| 115 | # /usr/local/bin/cron-task.sh |
| 116 | |
| 117 | # 日志文件 |
| 118 | LOG_FILE="/var/log/cron-task.log" |
| 119 | |
| 120 | # 锁文件（防止重复执行） |
| 121 | LOCK_FILE="/var/run/cron-task.lock" |
| 122 | |
| 123 | # 检查锁 |
| 124 | if [ -f "$LOCK_FILE" ]; then |
| 125 | echo "$(date): Task already running" >> "$LOG_FILE" |
| 126 | exit 1 |
| 127 | fi |
| 128 | |
| 129 | # 创建锁 |
| 130 | trap "rm -f $LOCK_FILE" EXIT |
| 131 | touch "$LOCK_FILE" |
| 132 | |
| 133 | # 记录开始 |
| 134 | echo "$(date): Task started" >> "$LOG_FILE" |
| 135 | |
| 136 | # 执行任务 |
| 137 | /path/to/actual/command >> "$LOG_FILE" 2>&1 |
| 138 | EXIT_CODE=$? |
| 139 | |
| 140 | # 记录结束 |
| 141 | echo "$(date): Task finished with exit code $EXIT_CODE" >> "$LOG_FILE" |
| 142 | |
| 143 | exit $EXIT_CODE |
| 144 | ``` |
| 145 | |
| 146 | ### Crontab 条目 |
| 147 | ```bash |
| 148 | # 推荐写法 |
| 149 | # 1. 使用绝对路径 |
| 150 | # 2. 重定向输出 |
| 151 | # 3. 添加注释 |
| 152 | |
| 153 | # 每日备份 - 凌晨2点 |
| 154 | 0 2 * * * /usr/local/bin/backup.sh >> /var/log/backup.log 2>&1 |
| 155 | |
| 156 | # 每5分钟健康检查 |
| 157 | */5 * * * * /usr/local/bin/healthcheck.sh > /dev/null 2>&1 |
| 158 | |
| 159 | # 每周日志清理 - 周日凌晨3点 |
| 160 | 0 3 * * 0 /usr/local/bin/cleanup-logs.sh >> /var/log/cleanup.log 2>&1 |
| 161 | ``` |
| 162 | |
| 163 | ### 环境变量 |
| 164 | ```bash |
| 165 | # 在 crontab 中设置 |
| 166 | SHELL=/bin/bash |
| 167 | PATH=/usr/local/bin:/usr/bin:/bin |
| 168 | HOME=/home/user |
| 169 | MAILTO=admin@example.com |
| 170 | |
| 171 | # 或在脚本中加载 |
| 172 | #!/bin/bash |
| 173 | source /etc/profile |
| 174 | source ~/.bashrc |
| 175 | ``` |
| 176 | |
| 177 | ## 日志与监控 |
| 178 | |
| 179 | ### 查看日志 |
| 180 | ```bash |
| 181 | # 系统日志 |
| 182 | grep CRON /var/log/syslog # Debian/Ubuntu |
| 183 | grep CRON /var/log/cron # CentOS/RHEL |
| 184 | |
| 185 | # 实时监控 |
| 186 | tail -f /var/log/syslog | grep CRON |
| 187 | |
| 188 | # 查看邮件（如果配置了 MAILTO） |
| 189 | cat /var/mail/username |
| 190 | ``` |
| 191 | |
| 192 | ### 调试技巧 |
| 193 | ```bash |
| 194 | # 手动测试脚本 |
| 195 | /usr/local/bin/myscript.sh |
| 196 | |
| 197 | # 模拟 cron 环境 |
| 198 | env -i /bin/bash --noprofile --norc -c '/usr/local/bin/myscript.sh' |
| 199 | |
| 200 | # 检查 cron 服务状态 |
| 201 | systemctl status cron # Debian/Ubuntu |
| 202 | systemctl status crond # CentOS/RHEL |
| 203 | ``` |
| 204 | |
| 205 | ## 常见场景 |
| 206 | |
| 207 | ### 场景 1：数据库备份 |
| 208 | ```bash |
| 209 | # 每天凌晨2点备份 MySQL |
| 210 | 0 2 * * * /usr/bin/mysqldump -u root -p'password' database | gzip > /backup/db_$(date +\%Y\%m\%d).sql.gz |
| 211 | |
| 212 | # 注意：% 需要转义为 \% |
| 213 | ``` |
| 214 | |
| 215 | ### 场景 2：日志轮转 |
| 216 | ```bash |
| 217 | # 每天压缩并清理7天前的日志 |
| 218 | 0 0 * * * find /var/log/myapp -name "*.log" -mtime +7 -delete |
| 219 | 0 1 * * * gzip /var/log/myapp/*.log.1 |
| 220 | ``` |
| 221 | |
| 222 | ### 场景 3：监控告警 |
| 223 | ```bash |
| 224 | # 每5分钟检查服务状态 |
| 225 | */5 * * * * /usr/local/bin/check-service.sh || /usr/local/bin/send-alert.sh |
| 226 | ``` |
| 227 | |
| 228 | ### 场景 4：使用 flock 防止重复 |
| 229 | ```bash |
| 230 | # 使用 flock 确保单实例运行 |
| 231 | */5 * * * * /usr/bin/flock -n /var/lock/mytask.lock /usr/local/bin/mytask.sh |
| 232 | ``` |
| 233 | |
| 234 | ## 故障排查 |
| 235 | |
| 236 | | 问题 | 排查方法 | |
| 237 | |------|----------| |
| 238 | | 任务不执行 | 检查 cron 服务状态、日志 | |
| 239 | | 权限错误 | 检查脚本权限、用户权限 | |
| 240 | | 环境变量问题 | 在脚本中设置 PATH | |
| 241 | | 命令找不到 | 使用绝对路径 | |
| 242 | | 输出丢失 | 重定向到日志文件 | |
| 243 | |
| 244 | ```bash |
| 245 | # 检查 cron 服务 |
| 246 | systemctl status cron |
| 247 | |
| 248 | # 检查用户是否被禁止 |
| 249 | cat /etc/cron.allow |
| 250 | cat /etc/cron.deny |
| 251 | |
| 252 | # 检查语法 |
| 253 | crontab -l | grep -v '^#' | while read line; do |
| 254 | echo "Checking: $line" |
| 255 | done |
| 256 | ``` |
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