RHEL7学习之crontab无法执行ntpdate

1，"/etc/crontab"文件

[root@localhost ~]# more /etc/crontab
SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# For details see man 4 crontabs

# Example of job definition:
# .---------------- minute (0 - 59)
# |  .------------- hour (0 - 23)
# |  |  .---------- day of month (1 - 31)
# |  |  |  .------- month (1 - 12) OR jan,feb,mar,apr ...
# |  |  |  |  .---- day of week (0 - 6) (Sunday=0 or 7) OR sun,mon,tue,wed,thu,fri,sat
# |  |  |  |  |
# *  *  *  *  * user-name  command to be executed

2，检查crond服务是否启动，crontab命令格式后，还是无法同步。查看crontab日志

From [email protected]  Sat Feb 13 00:43:01 2010
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From: "(Cron Daemon)" <[email protected]>
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Subject: Cron <root@localhost> root ntpdate -u  192.168.10.10
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X-Cron-Env: <XDG_SESSION_ID=68>
X-Cron-Env: <XDG_RUNTIME_DIR=/run/user/0>
X-Cron-Env: <LANG=en_US.UTF-8>
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <HOME=/root>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=root>
X-Cron-Env: <USER=root>
Message-Id: <20100212164301[email protected]>
Date: Sat, 13 Feb 2010 00:43:01 +0800 (CST)

/bin/sh: root: command not found

3，发现"/bin/sh: root: command not found"，需要改成绝对路径

[root@localhost ~]# whereis crontab
crontab: /usr/bin/crontab /etc/crontab /usr/share/man/man1/crontab.1.gz /usr/share/man/man5/crontab.5.gz
[root@localhost ~]# whereis clock
clock: /usr/sbin/clock /usr/share/man/man8/clock.8.gz

[root@localhost ~]# crontab -e

30 3 * * *  /usr/sbin/ntpdate -u  192.168.10.10; /usr/sbin/clock -w