Configuring cronie for mailing output [solved]

a_neutrino · 2013-06-25 03:08:08

Hi,
I am having a hard time setting up cronie for mailing output. Jump to the last sentence for the actual question.

From man 8 cron, I read that the -m option "allows you to specify a shell command to use for sending Cron mail output instead of using sendmail(8). This command must accept a fully formatted mail message (with headers) on standard input and send it as a mail message to the recipients specified in the mail headers". I do have msmtp installed. I can do this and receive email successfully:

$ msmtp -t << eof
> To: <my address>@gmail.com
> 
> test
> eof

Thus I know that msmtp -t is the command I must provide with the -m option.

Then, I followed these instructions and created /etc/systemd/system/cronie.service.d/mailing.conf which contains:

[Service]
ExecStart=
ExecStart=/usr/bin/crond -n -m 'msmtp -t'

Note: the first, empty ExecStart cancels the former one from the original .service file.

After starting cronie.service, this is the result of systemctl status cronie.service:

cronie.service - Periodic Command Scheduler
   Loaded: loaded (/usr/lib/systemd/system/cronie.service; enabled)
  Drop-In: /etc/systemd/system/cronie.service.d
           └─mailing.conf
   Active: active (running) since Mon 2013-06-24 22:58:24 EDT; 2s ago
 Main PID: 1457 (crond)
   CGroup: name=systemd:/system/cronie.service
           └─1457 /usr/bin/crond -n -m msmtp -t

Jun 24 22:58:24 electron systemd[1]: Started Periodic Command Scheduler.
Jun 24 22:58:24 electron crond[1457]: (CRON) INFO (Syslog will be used instead of sendmail.)
Jun 24 22:58:24 electron crond[1457]: (CRON) INFO (running with inotify support)
Jun 24 22:58:24 electron crond[1457]: (CRON) INFO (@reboot jobs will be run at computer's startup.)

It seems that systemd drops the single quotes and takes -t as it's own parameter instead of passing it to msmtp. You can also see that crond logged "Syslog will be used instead of sendmail". I can actually see the output of my commands in /var/log/crond.log. How should I quote the space between msmtp and -t in the ExecStart line of my .service file?

Last edited by a_neutrino (2013-06-30 21:54:53)

dif · 2013-06-27 08:52:04

Hi,

I cannot advise you how to add the "-t", but I think I can help you a bit.

Cron uses sendmail, so the easiest method to use msmtp instead of sendmail would be to create a symbolic link to msmtp:

sudo ln -s /usr/bin/msmtp /usr/bin/sendmail

Unfortunately this does not work as msmtp cannot figure out which e-mail address(es) to use instead of the user. You have to create a file /etc/aliases that holds the addresses where e-mail notifications will be sent to when a user's cronjob creates an output. For example:

root: myadmin@mydomain.com
user1: user1@domain1.com
default: another_address@domain2.com user2@his_domain.com

Note: Contrary to Wiki, there are no commas separating e-mail addresses if there are a few in a line.
You have to declare /etc/aliases for msmtp to find it. Best put it in /etc/msmtprc:

aliases /etc/aliases

There is a special script distributed with Arch that is able to scan /etc/aliases for a valid domain address and then calls msmtp. Here is its path

/usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh

Copy it to /usr/bin/ and create a simlink:

sudo cp /usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh /usr/bin/find_alias_for_msmtp.sh
sudo ln -s /usr/bin/find_alias_for_msmtp.sh /usr/bin/sendmail

/usr/local/bin/ could be a nice place for the script, too.
And that's is. When a cronjob generates an output, cron will run sendmail (linked to the script), and the script will find an e-mail address and run msmtp.

Remember to create separate .mailrc and .msmtprc files for root in his home directory.

Here is a cronjob command I used to test it:

echo $(/home/wm/bin/myip.sh) | mail -s info myaddress@mydomain.pl; echo HAHA

Output of myip.sh is e-mailed by mail (mailx). This not generates any output for cron to e-mail. But "echo HAHA" generates the output that is e-mailed by cron through sendmail. As a result, I receive two e-mails. The recipients may be different or the same, depending on the settings in /etc/aliases.

Hope this helps.

a_neutrino · 2013-06-28 00:10:04

Hi,
Thanks a lot for your help. The issue is [solved].

dif wrote:

You have to create a file /etc/aliases that holds the addresses where e-mail notifications will be sent to when a user's cronjob creates an output.

It seems unnecessary. The MAILTO variable set in the crontab accepts a complete email address.

dif wrote:

Contrary to Wiki, there are no commas separating e-mail addresses if there are a few in a line.

The msmtp man page also says to put commas.

dif wrote:

There is a special script distributed with Arch that is able to scan /etc/aliases for a valid domain address and then calls msmtp. Here is its path
/usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh
Copy it to /usr/bin/ and create a simlink:
sudo cp /usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh /usr/bin/find_alias_for_msmtp.sh
sudo ln -s /usr/bin/find_alias_for_msmtp.sh /usr/bin/sendmail

Why didn't you just :

chmod +x /usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh
ln -s /usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh /usr/bin/sendmail

Also, I had to modify the find_alias_for_msmtp.sh script a little because cronie calls sendmail without any parameters:

diff --git a/scripts/find_alias/find_alias_for_msmtp.sh b/scripts/find_alias/find_alias_for_msmtp.sh
index fb485dd..346f313 100644
--- a/scripts/find_alias/find_alias_for_msmtp.sh
+++ b/scripts/find_alias/find_alias_for_msmtp.sh
@@ -16,15 +16,18 @@ MSMTP=`which msmtp || echo "/usr/local/bin/msmtp"`
 #
 if [  "$1" = '-i'  ] ; then
    v_recipient=$2 # mailx calls sendmail with -i as the 1st param and the recipient as the second param
-elif [ "$1" = '-t' ] ; then  # most other programs call sendmail with a -t option
+elif [ "$1" = '-t' -o $# = 0 ] ; then  
+        # Most other programs call sendmail with a -t option.
+        # cronie calls sendmail without parameters and
+        # expects sendmail to find the recipient in the mail headers.
         v_to=`echo "$v_msg" | grep -m 1 'To: '`
         v_recipient=${v_to:4:50}
 else
-   v_recipient=$1 # no parameter, sendmail was called with the recipient as parameter
+   v_recipient=$1 # sendmail was called with the recipient as parameter
 fi
 #
 
-if [ $v_recipient != 0 ] ; then
+if [ "$v_recipient" != 0 ] ; then
 
 # trim spaces from recipient email address
  v_recipient="${v_recipient// /}"

Or maybe I missed something. I submitted the patch upstream to see if they think it's relevant.

dif wrote:

Hope this helps.

Yes, it did! Thank you so much.

dif · 2013-06-28 08:51:25

Hi,

(1) MAILTO seems very simple and nice, but I wanted to keep crontab just for my cronjobs.
How about a few addresses in one "MAILTO". Have you tried it? I mean normally you do not need multiple addresses, but it is nice to have such an option.

(2) Commas
That is a strange thing. Everywhere I read about it I saw the commas, but when I put them in the /etc/aliases no mail came to me from cron.
When I deleted them, e-mail started to come.

(3) The location /usr/share/doc/msmtp/find_alias/find_alias_for_msmtp.sh
Again your approach is simpler and nicer, but I wanted an executable script in /usr/bin/.
I am beginning to think of moving it to /usr/local/bin/ for my backup solution.

(4) Script modification
I have yet to read it. I am sure I learn from that. Thank you.
By the way, if upstream accepts your patch, your cron notifications will stop working because of (3). It is not a problem, just "chmod +x", but sometimes it is hard to find what has happened.

Last edited by dif (2013-06-28 09:13:20)

dif · 2013-06-30 15:35:36

This short script below (sm.sh) will tell you how cron calls sendmail and what the structure of cron's e-mail is.

echo -e "The sendmail call from cron:\n\t$0 $@" > /tmp/sm
MSG=$(cat)
echo -------e-mail_structure------- >> /tmp/sm
echo -e "$MSG" >> /tmp/sm
echo -------end_of_email----------- >> /tmp/sm

To use the script replace the sendmail link with the script

sudo rm /usr/bin/sendmail
sudo ln -s /path/to/sm.sh /usr/bin/sendmail

and set this cronjob command to run

echo $(date); echo cronjob:; cat /var/spool/cron/$USER; echo /etc/aliases:; cat /etc/aliases

Running this job cron will call sm.sh, and you will be able to see the parameters cron sends to sendmail in /tmp/sm. Note that the first parameter is "-FCronDaemon" and the last is the value of $USER.
Interestingly "-t" is also passed to sendmail.

The above information will help you modify find_alias_for_msmtp.sh.

P.S. Cron does not work with MAILTO="<USER1> <USER2>"

Last edited by dif (2013-06-30 15:36:54)

a_neutrino · 2013-06-30 21:54:09

Hi dif,

Your sm.sh script proved to be useful for debugging.

If cronie is started with the -m option (for example: -m /usr/local/bin/sm.sh), then it does not pass any parameters. Otherwise, it does call /usr/bin/sendmail with the parameters as you described. Therefore, I shall retract the patch I sent for find_alias_for_msmtp.sh.

Also, your script allowed me to find the answer to my #1 question! If I create this file /etc/systemd/system/cronie.service.d/mailing.conf:

[Service]
ExecStart=
ExecStart=/usr/bin/crond -n -m 'msmtp -t'

then the -t parameter is indeed passed to msmtp, even though the quotes are dropped in the reports from systemd. It did not work at first because I didn't have an /etc/aliases file or a MAILTO=complete@address.com line in my crontab. dcron, the former default scheduler, had a different way of getting the mailing address. From what I see in my system backups, I used to pass the -m parameter with the email address like so '-m email@address.com'.

Now I know and I summed up this knowledge in the wiki and marked this thread as solved.
Arch Wiki > Cron > Example with msmtp (created the section)
Arch Wiki > Msmtp > Configuring cron for msmtp (updated)

Arch Linux

#1 2013-06-25 03:08:08

Configuring cronie for mailing output [solved]

#2 2013-06-27 08:52:04

Re: Configuring cronie for mailing output [solved]

#3 2013-06-28 00:10:04

Re: Configuring cronie for mailing output [solved]

#4 2013-06-28 08:51:25

Re: Configuring cronie for mailing output [solved]

#5 2013-06-30 15:35:36

Re: Configuring cronie for mailing output [solved]

#6 2013-06-30 21:54:09

Re: Configuring cronie for mailing output [solved]

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