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Yum-cron 無法向 root 發送電子郵件
我正在嘗試調查我們的一台 CentOS 7 伺服器上的一個問題，該伺服器
yum-cron未能通過執行操作的結果向 root 發送電子郵件。它總是給出這個錯誤：
無法向 localhost 發送電子郵件：
$$ Errno 111 $$連接被拒絕
但是，我們還有其他具有相同配置的伺服器，這是唯一出現此類問題的伺服器。
以下是
yum-cron.conf內容：[commands] # What kind of update to use: # default = yum upgrade # security = yum --security upgrade # security-severity:Critical = yum --sec-severity=Critical upgrade # minimal = yum --bugfix update-minimal # minimal-security = yum --security update-minimal # minimal-security-severity:Critical = --sec-severity=Critical update-minimal update_cmd = default # Whether a message should be emitted when updates are available, # were downloaded, or applied. update_messages = yes # Whether updates should be downloaded when they are available. download_updates = yes # Whether updates should be applied when they are available. Note # that download_updates must also be yes for the update to be applied. apply_updates = yes # Maximum amout of time to randomly sleep, in minutes. The program # will sleep for a random amount of time between 0 and random_sleep # minutes before running. This is useful for e.g. staggering the # times that multiple systems will access update servers. If # random_sleep is 0 or negative, the program will run immediately. # 6*60 = 360 random_sleep = 360 [emitters] # Name to use for this system in messages that are emitted. If # system_name is None, the hostname will be used. system_name = None # How to send messages. Valid options are stdio and email. If # emit_via includes stdio, messages will be sent to stdout; this is useful # to have cron send the messages. If emit_via includes email, this # program will send email itself according to the configured options. # If emit_via is None or left blank, no messages will be sent. emit_via = email # The width, in characters, that messages that are emitted should be # formatted to. output_width = 80 [email] # The address to send email messages from. email_from = root # List of addresses to send messages to. email_to = root # Name of the host to connect to to send email messages. email_host = localhost [groups] # NOTE: This only works when group_command != objects, which is now the default # List of groups to update group_list = None # The types of group packages to install group_package_types = mandatory, default [base] # This section overrides yum.conf # Use this to filter Yum core messages # -4: critical # -3: critical+errors # -2: critical+errors+warnings (default) debuglevel = -2 # skip_broken = True mdpolicy = group:main # Uncomment to auto-import new gpg keys (dangerous) # assumeyes = True我仔細檢查過，它與其他伺服器上的配置文件相同。
此外，所有伺服器都
postfix安裝為郵件伺服器，使用 sendgrid 作為 smtp 中繼。最後，在所有
我應該檢查什麼才能使 cron 正確地向 root 發送電子郵件？
編輯：
經過一些測試，我注意到在有問題的伺服器上，沒有監聽 TCP 埠 25：
[root@srv1 ~]# ss -tnlp | grep :25 [root@srv1 ~]#在另一台伺服器上，我得到：
[root@srv2 ~]# ss -tnlp | grep :25 LISTEN 0 100 127.0.0.1:25 *:* users:(("master",pid=768,fd=13)) [root@srv2 ~]#PID 768 的程序在哪裡
/usr/libexec/postfix/master -w。然後，我檢查了哪些程序對
postfix服務處於活動狀態，並在我得到的第一台伺服器上：[root@srv1 ~]# service postfix status Redirecting to /bin/systemctl status postfix.service ● postfix.service - Postfix Mail Transport Agent Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled) Active: active (running) since Tue 2017-01-10 09:18:55 CET; 5min ago Process: 17409 ExecStop=/usr/sbin/postfix stop (code=exited, status=0/SUCCESS) Process: 17431 ExecStart=/usr/sbin/postfix start (code=exited, status=0/SUCCESS) Process: 17428 ExecStartPre=/usr/libexec/postfix/chroot-update (code=exited, status=0/SUCCESS) Process: 17421 ExecStartPre=/usr/libexec/postfix/aliasesdb (code=exited, status=0/SUCCESS) Main PID: 17503 (master) CGroup: /system.slice/postfix.service ├─17503 /usr/libexec/postfix/master -w ├─17504 pickup -l -t unix -u └─17505 qmgr -l -t unix -u而在第二個輸出是：
[root@srv2 ~]# service postfix status Redirecting to /bin/systemctl status postfix.service ● postfix.service - Postfix Mail Transport Agent Loaded: loaded (/usr/lib/systemd/system/postfix.service; enabled; vendor preset: disabled) Active: active (running) since Wed 2016-12-28 16:34:19 CET; 1 weeks 5 days ago Main PID: 768 (master) CGroup: /system.slice/postfix.service ├─ 768 /usr/libexec/postfix/master -w ├─ 770 qmgr -l -t unix -u ├─8185 pickup -l -t unix -u └─9148 tlsmgr -l -t unix -u所以看起來第一台伺服器
tlsmgr根本沒有啟動，但是我在日誌中找不到任何錯誤。
最後我發現這不是問題，
yum-cron而是postfix本身的配置問題。事實上，在第一台伺服器上，
master.cf文件是這樣的：# Postfix master process configuration file. For details on the format # of the file, see the master(5) manual page (command: "man 5 master"). # # Do not forget to execute "postfix reload" after editing this file. # # ========================================================================== # service type private unpriv chroot wakeup maxproc command + args # (yes) (yes) (yes) (never) (100) # ========================================================================== #smtp inet n - n - - smtpd #smtp inet n - n - 1 postscreen #smtpd pass - - n - - smtpd #dnsblog unix - - n - 0 dnsblog #tlsproxy unix - - n - 0 tlsproxy submission inet n - n - - smtpd [...]在第二台伺服器上是：
# Postfix master process configuration file. For details on the format # of the file, see the master(5) manual page (command: "man 5 master"). # # Do not forget to execute "postfix reload" after editing this file. # # ========================================================================== # service type private unpriv chroot wakeup maxproc command + args # (yes) (yes) (yes) (never) (100) # ========================================================================== smtp inet n - n - - smtpd #smtp inet n - n - 1 postscreen #smtpd pass - - n - - smtpd #dnsblog unix - - n - 0 dnsblog #tlsproxy unix - - n - 0 tlsproxy #submission inet n - n - - smtpd [...]並通過將第一個文件設置為第二個文件，即取消註釋第一
smtp行並刪除該submission行，我讓它按預期工作。