我正在尝试使用 cron 自动执行系统更新。您可以在下面看到我的 crontab、命令和导致的错误。
当我以 root 身份运行 upgrades.sh 时，脚本运行良好。当 cron 运行它时，apt-get -y update运行没有问题，但aptitude -y safe-upgrade失败了。我猜这个错误：debconf: (This frontend requires a controlling tty.)是因为有一个内核更新，反过来又更新了 grub，这需要我明确说明可以覆盖/boot/grub/menu.lst。但我不明白路径错误。我希望更新不需要我的监督就能完成。
我已经读完了这个问题及其尚未被接受的解决方案unattended-upgrades，我可能最终会使用它，但为什么我不能使用 cron？ 看起来它应该非常简单，而且更符合 Linux 风格。
定时任务
root@daedalus:~/bin# crontab -l
# m h dom mon dow command
45 06 * * * ~/bin/upgrades.sh
升级.sh
root@daedalus:~/bin# cat upgrades.sh
#!/bin/bash
/usr/bin/apt-get -y update
/usr/bin/aptitude -y safe-upgrade
错误
debconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Readline
debconf: unable to initialize frontend: Readline
debconf: (This frontend requires a controlling tty.)
debconf: falling back to frontend: Teletype
dpkg-preconfigure: unable to re-open stdin:
Fetched 37.6MB in 4min 23s (143kB/s)
dpkg: warning: 'ldconfig' not found on PATH.
dpkg: warning: 'start-stop-daemon' not found on PATH.
dpkg: warning: 'update-rc.d' not found on PATH.
dpkg: 3 expected program(s) not found on PATH.
NB: root's PATH should usually contain /usr/local/sbin, /usr/sbin and /sbin.
E: Sub-process /usr/bin/dpkg returned an error code (2)
A package failed to install. Trying to recover:
dpkg: warning: 'ldconfig' not found on PATH.
dpkg: warning: 'start-stop-daemon' not found on PATH.
dpkg: warning: 'update-rc.d' not found on PATH.
dpkg: 3 expected program(s) not found on PATH.
NB: root's PATH should usually contain /usr/local/sbin, /usr/sbin and /sbin.
Reading package lists...
Building dependency tree...
Reading state information...
Reading extended state information...
Initializing package states...
Writing extended state information...
答案1
虽然您的主要问题已经得到解答，但您似乎收到了 debconf 警告，因为您在没有交互式 tty 的情况下运行 apt-get。要消除这些消息，您可以设置此环境变量：
DEBIAN_FRONTEND=noninteractive
答案2
这些消息告诉您您的PATH环境变量是错误的。
尝试添加
PATH=/usr/bin:/bin:/usr/sbin:/sbin
到你的顶部crontab。
或者你可以把相同的PATH行作为第二行~/bin/upgrades.sh。这样，你从命令行进行的测试和从进行的测试crontab应该产生相同的结果。
答案3
有一个社区维基页面：crontab 不起作用的原因。在这种情况下，原因似乎是 cron 的环境变量有限。您可以从 /etc/cron.daily 中的 shell 脚本运行此脚本吗？
答案4
从Cron如何操作：
根据正在运行的命令，您可能需要通过将以下行放在其 crontab 文件的顶部来扩展 root 用户的 PATH 变量：
PATH=/usr/sbin:/usr/bin:/sbin:/bin
但事实上，做和你一样的事情似乎一切都很好......你从哪里获取这些错误？
计划任务：
root@PORTATIL:/var/log$ crontab -l
* * */2 * * /usr/share/myupdate.sh > /var/log/myupdate.log
脚本：
root@PORTATIL:/etc# cat /usr/share/myupdate.sh
#!/bin/bash
#Testing updates
apt-get update -y
apt-get upgrade -y
日志：
root@PORTATIL:/etc# cat /var/log/myupdate.log
Hit http://security.ubuntu.com lucid-security Release.gpg
Hit http://archive.canonical.com lucid Release.gpg
Hit http://archive.canonical.com lucid Release.gpg
Hit http://packages.medibuntu.org lucid Release.gpg
Get:1 http://dl.google.com stable Release.gpg [197B]
Hit http://ppa.launchpad.net lucid Release.gpg
Hit http://ppa.launchpad.net lucid Release.gpg
Hit http://ppa.launchpad.net lucid Release.gpg
Hit http://security.ubuntu.com lucid-security Release
Hit http://badgerports.org lucid Release.gpg
Hit http://archive.canonical.com lucid Release
Hit http://ppa.launchpad.net lucid Release.gpg
Hit http://ppa.launchpad.net maverick Release.gpg
Hit http://ppa.launchpad.net lucid Release.gpg
Hit http://ppa.launchpad.net lucid Release.gpg
Hit http://ppa.launchpad.net lucid Release.gpg
Get:2 http://dl.google.com stable Release [1347B]
Hit http://security.ubuntu.com lucid-security/main Packages
Hit http://ppa.launchpad.net lucid Release
Hit http://ppa.launchpad.net lucid Release
Hit http://packages.medibuntu.org lucid Release
Hit http://download.virtualbox.org lucid Release.gpg
Hit http://archive.canonical.com lucid Release
Hit http://linux.dropbox.com lucid Release.gpg
Get:3 http://dl.google.com stable/main Packages [1110B]
Hit http://security.ubuntu.com lucid-security/restricted Packages
Hit http://security.ubuntu.com lucid-security/main Sources
Hit http://security.ubuntu.com lucid-security/restricted Sources
Hit http://security.ubuntu.com lucid-security/universe Packages
Hit http://security.ubuntu.com lucid-security/universe Sources
Hit http://ppa.launchpad.net lucid Release
Hit http://ppa.launchpad.net lucid Release
Hit http://ppa.launchpad.net maverick Release
Hit http://ppa.launchpad.net lucid Release
Hit http://ppa.launchpad.net lucid Release
Hit http://badgerports.org lucid Release
Hit http://archive.canonical.com lucid/partner Packages
Hit http://security.ubuntu.com lucid-security/multiverse Packages
Hit http://security.ubuntu.com lucid-security/multiverse Sources
Hit http://ppa.launchpad.net lucid Release
Hit http://packages.medibuntu.org lucid/free Packages
Hit http://download.virtualbox.org lucid Release
Hit http://es.archive.ubuntu.com lucid Release.gpg
Hit http://linux.dropbox.com lucid Release
Hit http://archive.canonical.com lucid/partner Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://es.archive.ubuntu.com lucid-updates Release.gpg
Hit http://badgerports.org lucid/main Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://ppa.launchpad.net maverick/main Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://packages.medibuntu.org lucid/non-free Packages
Hit http://linux.dropbox.com lucid/main Packages
Hit http://es.archive.ubuntu.com lucid Release
Hit http://download.virtualbox.org lucid/contrib Packages
Hit http://ppa.launchpad.net lucid/main Packages
Hit http://es.archive.ubuntu.com lucid-updates Release
Hit http://es.archive.ubuntu.com lucid/main Packages
Hit http://es.archive.ubuntu.com lucid/restricted Packages
Hit http://es.archive.ubuntu.com lucid/main Sources
Hit http://es.archive.ubuntu.com lucid/restricted Sources
Hit http://es.archive.ubuntu.com lucid/universe Packages
Hit http://es.archive.ubuntu.com lucid/universe Sources
Hit http://es.archive.ubuntu.com lucid/multiverse Packages
Hit http://es.archive.ubuntu.com lucid/multiverse Sources
Hit http://es.archive.ubuntu.com lucid-updates/main Packages
Hit http://es.archive.ubuntu.com lucid-updates/restricted Packages
Hit http://es.archive.ubuntu.com lucid-updates/main Sources
Hit http://es.archive.ubuntu.com lucid-updates/restricted Sources
Hit http://es.archive.ubuntu.com lucid-updates/universe Packages
Hit http://es.archive.ubuntu.com lucid-updates/universe Sources
Hit http://es.archive.ubuntu.com lucid-updates/multiverse Packages
Hit http://es.archive.ubuntu.com lucid-updates/multiverse Sources
Fetched 2654B in 1s (1628B/s)
Reading package lists...
Reading package lists...
Building dependency tree...
Reading state information...
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.