【Do家】Linux下crontab执行非os自带命令注意事项

【场景】通过crontab执行java命令

【问题】尽管已设置/etc/profile和/root/.bash_profile中环境变量
////////begin//////
# remedied by can_do on 2020-03-07
export JAVA_HOME=/opt/jdk
export PATH=${JAVA_HOME}/bin:${PATH}
export CLASSPATH=.:${JAVA_HOME}/lib/tools.jar:${JAVA_HOME}/lib/dt.jar:${JAVA_HOME}/jre/lib/rt.jar
////////end////////

但crontab中设置的java命令还是不能执行，而在root用户的shell窗口下是可以成功执行java命令的，说明环境变量配置是OK。


////////////execute in failure///////begin/////
From [e-mail]  Thu Jun 24 20:42:02 2021
Return-Path: <[e-mail]>
X-Original-To: root
Delivered-To: [e-mail]
Received: by cnd-centos.localdomain (Postfix, from userid 0)
id 2A2A761C20; Thu, 24 Jun 2021 20:42:02 +0800 (CST)
From: "(Cron Daemon)" <[e-mail]>
To: [e-mail]
Subject: Cron <root@cnd-centos> /opt/shell/yourShellScript.sh
Content-Type: text/plain; charset=UTF-8
Auto-Submitted: auto-generated
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X-Cron-Env: <XDG_SESSION_ID=13>
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: <[e-mail]>
Date: Thu, 24 Jun 2021 20:42:02 +0800 (CST)

/opt/shell/yourShellScript.sh: line 9: jstat: command not found
/opt/shell/yourShellScript.sh: line 11: jstat: command not found
The current pid is 1876.
Eden percent is .
Old percent is .
/opt/shell/yourShellScript.sh: line 21: [: -gt: unary operator expected
////////////execute in failure///////end/////


【解决方法】
显示告诉os，通过root用户执行java命令，如下：

su - -c "/opt/shell/yourShellScript.sh"

////////////execute in success/////////begin///////
From [e-mail]  Thu Jun 24 20:44:02 2021
Return-Path: <[e-mail]>
X-Original-To: root
Delivered-To: [e-mail]
Received: by cnd-centos.localdomain (Postfix, from userid 0)
id 5A47961C20; Thu, 24 Jun 2021 20:44:02 +0800 (CST)
From: "(Cron Daemon)" <[e-mail]>
To: [e-mail]
Subject: Cron <root@cnd-centos> su - -c "/opt/shell/yourShellScript.sh"
Content-Type: text/plain; charset=UTF-8
Auto-Submitted: auto-generated
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X-Cron-Env: <XDG_SESSION_ID=15>
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: <[e-mail]>
Date: Thu, 24 Jun 2021 20:44:02 +0800 (CST)

The current pid is 1876.
Eden percent is 20.
Old percent is 3.
////////////execute in success/////////end///////

【小结】
1> 引起该问题的原因，是多用户下导致的环境变量选择问题，su -相当切到root下执行，前提是环境变量已配置ok；
2> Linux启动脚本/etc/rc.local中命令执行不成功，除了chmod +x权限外,也需要调整为su -  -c "yourScript"
3> 通过系统日志分析问题原因tail -f /var/log/boot.log，也是关键一步；

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