After cron starts a scheduled task, it always starts a [Sendmail] process solution. After each cron task, msmtp. Log always records a log of failed sending.

When a task is automatically compiled on the recently configured server, after each cron task is executed, the msmtp log file in the home root directory contains a failed log, the receiver is the user name used to execute the cron task. In fact, the cron task is output to a large number of standard devices. Therefore, Sendmail of the system wants to send the output information to the user as an email, this user does not have a mailbox, so msmtp records the log of failed sending. The process of trying to send the mail is the [Sendmail] <defunct> process, if you delete the soft link from Sendmail to msmtp, the process will become [cron] <defunct>.

Therefore, the solution to this problem is to direct the cron task output to an empty device: 1>/dev/null 2> & 1