Many times we will encounter this situation. We have worked hard to write a script. After testing, everything is normal, and then put it into crontab to execute. As a result, no matter how it is configured, the execution is abnormal.
It turned out that environmental problems were actually the culprit of this anomaly.
We first execute the env command on our server, which appears as follows:
XDG_VTNR=1
XDG_SESSION_ID=1
HOSTNAME=bogon
IMSETTINGS_INTEGRATE_DESKTOP=yes
GPG_AGENT_INFO=/run/user/0/keyring/gpg:0:1
VTE_VERSION=3802
TERM=xterm
SHELL=/bin/bash
XDG_MENU_PREFIX=gnome-
HISTSIZE=1000
GJS_DEBUG_OUTPUT=stderr
WINDOWID=37748743
GJS_DEBUG_TOPICS=JS ERROR;JS LOG
IMSETTINGS_MODULE=IBus
QT_GRAPHICSSYSTEM_CHECKED=1
USER=root
SSH_AUTH_SOCK=/run/user/0/keyring/ssh
USERNAME=root
SESSION_MANAGER=local/unix:@/tmp/.ICE-unix/1672,unix/unix:/tmp/.ICE-unix/1672
PATH=/usr/local/bin:/usr/local/sbin:/usr/bin:/usr/sbin:/bin:/sbin:/root/bin
MAIL=/var/spool/mail/root
DESKTOP_SESSION=gnome
QT_IM_MODULE=ibus
PWD=/root
XMODIFIERS=@im=ibus
LANG = zh_CN.UTF-8
GDM_LANG=zh_CN.UTF-8
KDEDIRS=/usr
GDMSESSION=gnome
SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass
HISTCONTROL=ignoredups
HOME=/root
XDG_SEAT=seat0
SHLVL=2
GNOME_DESKTOP_SESSION_ID=this-is-deprecated
XDG_SESSION_DESKTOP=gnome
LOGNAME=root
DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-VQpgyslPbO,guid=0b7c6ec0e15a92dd89a8eaf654f84153
LESSOPEN=||/usr/bin/lesspipe.sh %s
WINDOWPATH=1
XDG_RUNTIME_DIR=/run/user/0
DISPLAY=:0
XDG_CURRENT_DESKTOP=GNOME
XAUTHORITY=/run/gdm/auth-for-root-A4DlSi/database
_=/usr/bin/env
然后我们编辑一个crontab,如下:
* * * * * env > /home/crontab.out
然后我们在/home/crontab.out文件中,看看里面的内容。令人奇怪的是,我们发现的里面的信息只有
XDG_SESSION_ID=3
SHELL=/bin/sh
USER=root
PATH=/usr/bin:/bin
PWD=/root
LANG=zh_CN.UTF-8
SHLVL=1
HOME=/root
LOGNAME=root
XDG_RUNTIME_DIR=/run/user/0
_=/usr/bin/env
我们先不讨论原因,这里,我们就可以看到为什么很多脚本在crontab中编辑后不可以运行了。因为crontab的任务环境就没有定义那么多的环境变量,我们在交互式的环境下写的脚本中用到了这些没有的环境变量,当然可以通过,但是放到crontab下就不行了。
那么这些环境变量居然差那么多,为什么呢?因为系统的cron deamon会自动设置可构成最小环境的环境变量。
解决方案可以有两种:
1. 定义好一些环境参数,并在crontab里面先source生效,再执行主程序脚本
2. 直接把脚本中的环境变量改为绝对路径。
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