有群里的小伙伴说crontab里的任务不执行，具体是这样的
*/1 * * * * /bin/date "+%Y-%m-%d %H:%M:%S" >>/data/tmp/test.log
我试了下在命令行可以执行，定时任务确实不执行，于是去翻了下日志：
#tail -f /var/spool/mail/root X-Cron-Env: <HOME=/root> X-Cron-Env: <PATH=/usr/bin:/bin> X-Cron-Env: <LOGNAME=root> X-Cron-Env: <USER=root> Message-Id: <20200108081701.8FD502100481@D3L40.localdomain> Date: Wed, 8 Jan 2020 16:17:01 +0800 (CST) /bin/sh: -c: line 0: unexpected EOF while looking for matching `"' /bin/sh: -c: line 1: syntax error: unexpected end of file From root@D3L40.localdomain Wed Jan 8 16:18:01 2020
说是语法错误，结尾不对，明明是两个双引号啊，这样就有可能是里面有特殊字符导致命令意外中断了，于是查了下万能的百度发现：
The “sixth” field (the rest of the line) specifies the command to be run. The entire command portion of the line, up to a newline or % character, will be executed by /bin/sh or by the shell specified in the SHELL variable of the crontab file. Percent-signs (%) in the command, unless escaped with backslash (), will be changed into newline characters, and all data after the first % will be sent to the command as standard input. There is no way to split a single command line onto multiple lines, like the shell’s trailing “”.
大概是在crontab里%当换行符用了，想要正常使用就得加反引号，\%这样来用。
于是把命令改成了：
*/1 * * * * /bin/date "+%Y-%m-%d %H:%M:%S" >>/data/tmp/test.log
最后：
# cat test.log 2020-01-08 16:38:01 2020-01-08 16:39:01
可以了，于是想着记一下，好记性不如烂笔头嘛。