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My server crashed today, and was offline for about 1 hour when I noticed it...

The Daily Process Log shows the following:

user --- %cpu
mailnull - 958 - /usr/sbin/sendmail -FCronDaemon -i -odi -oem -oi -t

This makes me think that what cause the server crash was sendmail that created a high server load...

I dont have any website on my server that sends a lot of emails, so I dont know what caused this. Do you have any idea?

And, how can I disable sendmail?

Will I stop receiving emails from my server if I stop it?

Thanks.

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what OS flavor are you running? –  pablo Feb 14 '11 at 17:18

5 Answers 5

up vote 1 down vote accepted

Check /var/log/mail.log to see if you were sending a lot of mail.

Disabling the daemon will not necessarily mean you will stop getting mail. It will disable mail sent by connecting to your SMTP port. It will also disable retries for mail which couldn't be delivered immediately. You should be able to setup sendmail to only run the periodic queue processes, without running the daemon.

Not running the daemon will also prevent incoming mail from other servers. If you were accidentally running an open relay, it will be shut down.

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Ah. Cpanel.

Well, disabling Sendmail and not replacing it with another mail package like Exim or Postfix will mean that you won't be able to send mail from your server. So yes, this will mean you will stop receiving messages from your server.

More than likely the real problem is that some spammer is using your system to send mail. There are several other methods to prevent this from happening, and I recommend looking into them.

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One reason for high cpu might be spam. I would also recordmend you to check you are not blacklisted example mxtoolbox.com. your servers might also be putted as sender, so undelivered mail-notices are sended to you.

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Disabling the sendmail daemon will NOT break getting mail off the server.

Email can/will still be sent originating from the server by calling the sendmail binary.

Disabling the sendmail daemon means the server no longer acts as an MTA.

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I guess that depends on whether or not "disabling" the daemon means removing it from your server, or removing it from the startup scripts. –  Ernie Feb 14 '11 at 19:16

Contrary to popular belief this has nothing to do with incoming email. The process that generates the high CPU load is sending mail and it's done by the Cron Daemon. Disabling sendmail SMTP listener will not fix your problem.

Most likely you have a cron script running that generates tons of output and sendmail is trying to mail it. This also assumes that the 958 is actual CPU load, which seems rather high and is more likely to be the numeric user id, but that's another story.

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