cron 任務中的“apt-get -y upgrade”執行但不升級系統
該伺服器執行 Debian 7，我面臨著一個很大的謎團。
這是我的 cron 任務：
$ sudo crontab -e 42 15 * * * apt-get -y update >> /var/log/my-apt-update.txt 52 15 * * * apt-get -y upgrade >> /var/log/my-apt-upgrade.txt我添加了該
">> /var/log/my-apt-upgrade.txt"部分，因為我試圖了解為什麼我的系統永遠不會升級。cron 任務執行。每天我在 /var/log/syslog 中都有這些行：
Nov 14 15:42:01 myhostname /USR/SBIN/CRON[3374]: (root) CMD (apt-get -y update >> /var/log/my-apt-update.txt) Nov 14 15:52:01 myhostname /USR/SBIN/CRON[3394]: (root) CMD (apt-get -y upgrade >> /var/log/my-apt-upgrade.txt)並且 /var/log/my-apt-upgrade.txt 有這樣的段落（我只顯示最後兩天）：
Reading package lists... Building dependency tree... Reading state information... The following packages will be upgraded: file libmagic1 2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B/256 kB of archives. After this operation, 110 kB disk space will be freed. Reading package lists... Building dependency tree... Reading state information... The following packages will be upgraded: file libmagic1 2 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B/256 kB of archives. After this operation, 110 kB disk space will be freed.如您所見，包“file”和“libmagic1”應該在第一天就升級了。但他們不是。所以第二天，他們再次被提及。但沒有升級。
而今天，如果我跑
$ sudo apt-get -y upgrade再次提到包“file”和“libmagic1”並且它們得到了升級（最後）。
因此，如您所見，我可以手動升級。但是這些包應該在 cron 任務執行時就已經升級了。
關於這個謎團的任何線索？
11 月 15 日星期六 11:48 補充：
這是我的 /var/log/apt/history.log 在 cron 作業期間出現的內容。
Start-Date: 2014-11-13 15:52:03 Commandline: apt-get -y upgrade Upgrade: file:amd64 (5.11-2+deb7u5, 5.11-2+deb7u6), libmagic1:amd64 (5.11-2+deb7u5, 5.11-2+deb7u6) Error: Sub-process /usr/bin/dpkg returned an error code (2) End-Date: 2014-11-13 15:52:03 Start-Date: 2014-11-14 15:52:03 Commandline: apt-get -y upgrade Upgrade: file:amd64 (5.11-2+deb7u5, 5.11-2+deb7u6), libmagic1:amd64 (5.11-2+deb7u5, 5.11-2+deb7u6) Error: Sub-process /usr/bin/dpkg returned an error code (2) End-Date: 2014-11-14 15:52:03不同包的 /var/log/apt/history.log 中會出現相同類型的消息。例如，本月早些時候，“wget”軟體包需要一些更新（這次我嘗試使用 -qq 選項，但這個選項似乎沒有任何區別）。
Start-Date: 2014-11-03 15:52:02 Commandline: apt-get -y -qq upgrade Upgrade: wget:amd64 (1.13.4-3+deb7u1, 1.13.4-3+deb7u2) Error: Sub-process /usr/bin/dpkg returned an error code (2) End-Date: 2014-11-03 15:52:02 Start-Date: 2014-11-04 15:52:02 Commandline: apt-get -y -qq upgrade Upgrade: wget:amd64 (1.13.4-3+deb7u1, 1.13.4-3+deb7u2) Error: Sub-process /usr/bin/dpkg returned an error code (2) End-Date: 2014-11-04 15:52:03 Start-Date: 2014-11-05 15:52:03 Commandline: apt-get -y -qq upgrade Upgrade: wget:amd64 (1.13.4-3+deb7u1, 1.13.4-3+deb7u2) Error: Sub-process /usr/bin/dpkg returned an error code (2) End-Date: 2014-11-05 15:52:03
看來我找到了問題的原因。
為了檢測錯誤，我必須在我的自定義日誌中擷取 stderr。事實證明這樣做很有用，因為一些錯誤沒有郵寄到 root，也沒有寫入其他日誌。
為了在我的日誌中擷取 stderr，我首先將 cron 任務更改為：
52 15 * * * apt-get -y upgrade >> /var/log/my-apt-upgrade.txt 2>&1今天要更新包“wlibgcrypt11”。這一次，我的日誌發現了一個錯誤。它比之前在 /var/log/apt/history.log 中出現的模糊錯誤消息更明確。
今天在 /var/log/my-apt-upgrade.txt 中：
Reading package lists... Building dependency tree... Reading state information... The following packages will be upgraded: libgcrypt11 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: 1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded. Need to get 0 B/300 kB of archives. After this operation, 35.8 kB of additional disk space will be used. dpkg: warning: 'ldconfig' not found in PATH or not executable dpkg: warning: 'start-stop-daemon' not found in PATH or not executable dpkg: error: 2 expected programs not found in PATH or not executable Note: root's PATH should usually contain /usr/local/sbin, /usr/sbin and /sbin E: Sub-process /usr/bin/dpkg returned an error code (2)所以這是一個PATH錯誤。
我係統上的根路徑包含所有必需的目錄。visudo 中的secure_path 變數也是如此。這就是為什麼當我手動執行 sudo apt-get 時一切正常的原因。
但是 cron 沒有設置環境變數。所以我為每個 cron 任務添加了一個 PATH 環境變數。
$ sudo crontab -e 22 16 * * * PATH='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin' apt-get -y update >> /var/log/my-new-apt-update.txt 2>&1 32 16 * * * PATH='/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin' apt-get -y upgrade >> /var/log/my-new-apt-upgrade.txt 2>&1它奏效了！cron 任務成功更新了包。