background

You have mail will be prompted when you open the built-in shell or iterm on the Mac computer. I didn’t care before, because I am engaged in network security work. I usually operate and plan tasks when studying the Mac. I did test it before, but it has been cleared manually, but why is there such a prompt?

process

The overall process should be as follows: first, the mail mechanism of MAC itself, especially the problem of planned tasks, that is, if the machine planned tasks are not executed as expected, it will report errors, The error result will be sent to the user in the form of e-mail and stored in:/var/mail/user name. This file is also true for Linux. So when you open the shell, you will be reminded that there are emails here. Because the SH script executed in the planned task was deleted when the planned task was created, but the planned task itself was not deleted, so the planned task reported an error and sent a lot of emails. At this time, the message received is: you have new mail, but after the prompt is completed, After that, the prompt becomes you have mail. Use the mail command to view the specific mail content:

From [email protected]  Mon Aug 30 11:24:01 2021
X-Original-To: hait
Delivered-To: [email protected]
From: [email protected] (Cron Daemon)
To: [email protected]
Subject: Cron <hait@B61zz> /tmp/evil.sh
X-Cron-Env: <SHELL=/bin/sh>
X-Cron-Env: <PATH=/usr/bin:/bin>
X-Cron-Env: <LOGNAME=hait>
X-Cron-Env: <USER=hait>
Date: Mon, 30 Aug 2021 11:24:00 +0800 (CST)
/bin/sh: /tmp/evil.sh: No such file or directory

Analyze the reason: it can be judged from the time that it is the email in August, which makes sense at this time. The whole process:

1. Establish the planned task and run normally;

2. Delete the SH file executed by the planned task, resulting in an error message, and then send the e-mail.

3. Delete the planned task (stop sending the error message);

4. Message unread always prompt

Solution:

1. You can directly turn off the terminal mailbox function. The link above has the command (I failed, I used plan2)

2. Delete this folder:/var/mail/user name