rsyslog

The rocket-fast system for log processing

ommail: Mail Output Module

Module Name: ommail
Available Since: 3.17.0
Author: Rainer Gerhards <rgerhards@adiscon.com>

This module supports sending syslog messages via mail. Each syslog message is sent via its own mail. Obviously, you will want to apply rigorous filtering, otherwise your mailbox (and mail server) will be heavily spammed. The ommail plugin is primarily meant for alerting users. As such, it is assumed that mails will only be sent in an extremely limited number of cases.

Ommail uses up to two templates, one for the mail body and optionally one for the subject line. Note that the subject line can also be set to a constant text. If neither the subject nor the mail body is provided, a quite meaningless subject line is used and the mail body will be a syslog message just as if it were written to a file. It is expected that the users customizes both messages. In an effort to support cell phones (including SMS gateways), there is an option to turn off the body part at all. This is considered to be useful to send a short alert to a pager-like device. It is highly recommended to use the

action.execonlyonceeveryinterval="<seconds>"

parameter to limit the amount of mails that potentially be generated. With it, mails are sent at most in a <seconds> interval. This may be your life safer. And remember that an hour has 3,600 seconds, so if you would like to receive mails at most once every two hours, include a

action.execonlyonceeveryinterval="7200"

in the action definition. Messages sent more frequently are simpy discarded.

Configuration Parameters

Configuration parameters are supported starting with v8.5.0. Earlier v7 and v8 versions did only support legacy parameters.

Note: parameter names are case-insensitive.

Action Parameters

server <server-name>

Mandatory

Name or IP address of the SMTP server to be used. Must currently be set. The default is 127.0.0.1, the SMTP server on the local machine. Obviously it is not good to expect one to be present on each machine, so this value should be specified.

port <port-number-or-name>

Mandatory

Port number or name of the SMTP port to be used. The default is 25, the standard SMTP port.

mailfrom <sender-address>

Mandatory

The email address used as the senders address.

mailto <recipient-addresses>

Mandatory

The recipient email address(es). Note that this is an array parameter. See samples below on how to specify multiple recipients.

subject.template <template-name>

Default: none, but may be left out

The name of the template to be used as the mail subject.

If you want to include some information from the message inside the template, you need to use subject.template with an appropriate template. If you just need a constant text, you can simply use subject.text instead, which doesn’t require a template definition.

subject.text <subject-string>

Default: none, but may be left out

This is used to set a constant subject text.

body.enable <boolean>

Default: on

Setting this to “off” permits to exclude the actual message body. This may be useful for pager-like devices or cell phone SMS messages. The default is “on”, which is appropriate for allmost all cases. Turn it off only if you know exactly what you do!

template <template-name>

Default: RSYSLOG_FileFormat

Template to be used for the mail body (if enabled).

The template.subject and template.text parameters cannot be given together inside a single action definition. Use either one of them. If none is used, a more or less meaningless mail subject is generated (we don’t tell you the exact text because that can change - if you want to have something specific, configure it!).

Caveats/Known Bugs

The current ommail implementation supports SMTP-direct mode only. In that mode, the plugin talks to the mail server via SMTP protocol. No other process is involved. This mode offers best reliability as it is not depending on any external entity except the mail server. Mail server downtime is acceptable if the action is put onto its own action queue, so that it may wait for the SMTP server to come back online. However, the module implements only the bare SMTP essentials. Most importantly, it does not provide any authentication capabilities. So your mail server must be configured to accept incoming mail from ommail without any authentication needs (this may be change in the future as need arises, but you may also be referred to sendmail-mode).

In theory, ommail should also offer a mode where it uses the sendmail utility to send its mail (sendmail-mode). This is somewhat less reliable (because we depend on an entity we do not have close control over - sendmail). It also requires dramatically more system ressources, as we need to load the external process (but that should be no problem given the expected infrequent number of calls into this plugin). The big advantage of sendmail mode is that it supports all the bells and whistles of a full-blown SMTP implementation and may even work for local delivery without a SMTP server being present. Sendmail mode will be implemented as need arises. So if you need it, please drop us a line (I nobody does, sendmail mode will probably never be implemented).

Examples

The following example alerts the operator if the string “hard disk fatal failure” is present inside a syslog message. The mail server at mail.example.net is used and the subject shall be “disk problem on <hostname>”. Note how \r\n is included inside the body text to create line breaks. A message is sent at most once every 6 hours (21600 seconds), any other messages are silently discarded (or, to be precise, not being forwarded - they are still being processed by the rest of the configuration file).

module(load="ommail")

template (name="mailBody"  type="string" string="RSYSLOG Alert\\r\\nmsg='%msg%'")
template (name="mailSubject" type="string" string="disk problem on %hostname%")

if $msg contains "hard disk fatal failure" then {
   action(type="ommail" server="mail.example.net" port="25"
           mailfrom="rsyslog@example.net"
           mailto="operator@example.net"
           subject.template="mailSubject"
           action.execonlyonceeveryinterval="21600")
}

The following example is exactly like the first one, but it sends the mails to two different email addresses:

module(load="ommail")

template (name="mailBody"  type="string" string="RSYSLOG Alert\\r\\nmsg='%msg%'")
template (name="mailSubject" type="string" string="disk problem on %hostname%")

if $msg contains "hard disk fatal failure" then {
   action(type="ommail" server="mail.example.net" port="25"
           mailfrom="rsyslog@example.net"
           mailto=["operator@example.net", "admin@example.net"]
           subject.template="mailSubject"
           action.execonlyonceeveryinterval="21600")
}

Note the array syntax to specify email addresses. Note that while rsyslog permits you to specify as many recipients as you like, your mail server may limit their number. It is usually a bad idea to use more than 50 recipients, and some servers may have lower limits. If you hit such a limit, you could either create additional actions or (recommended) create an email distribution list.

The next example is again mostly equivalent to the previous one, but it uses a constant subject line, so no subject template is required:

module(load="ommail")

template (name="mailBody"  type="string" string="RSYSLOG Alert\\r\\nmsg='%msg%'")

if $msg contains "hard disk fatal failure" then {
   action(type="ommail" server="mail.example.net" port="25"
           mailfrom="rsyslog@example.net"
           mailto=["operator@example.net", "admin@example.net"]
           subject.text="rsyslog detected disk problem"
           action.execonlyonceeveryinterval="21600")
}

Legacy Configuration Parameters

Note that the legacy configuration parameters do not affect new-style action definitions via the action() object. This is by design. To set default for action() objects, use module parameters in the

module(load="builtin:ommail" ...)

object.

Read about the importance of order in legacy configuration to understand how to use these configuration parameters. Legacy parameters should NOT be used when writing new configuration files.

  • $ActionMailSMTPServer

    equivalent to the server action parameter.

  • $ActionMailSMTPPort

    equivalent to the port action parameter.

  • $ActionMailFrom

    equivalent to the mailfrom action parameter.

  • $ActionMailTo

    mostly equivalent to the mailto action parameter. However, to specify multiple recpients, repeat this directive as often as needed. Note: This directive must be specified for each new action and is automatically reset. [Multiple recipients are supported for 3.21.2 and above.]

  • $ActionMailSubject

    equivalent to the subject.template action parameter.

  • $ActionMailEnableBody

    equivalent to the body.enable action parameter.

Legacy Examples

The following sample alerts the operator if the string “hard disk fatal failure” is present inside a syslog message. The mail server at mail.example.net is used and the subject shall be “disk problem on <hostname>”. Note how \r\n is included inside the body text to create line breaks. A message is sent at most once every 6 hours, any other messages are silently discarded (or, to be precise, not being forwarded - they are still being processed by the rest of the configuration file).

$ModLoad ommail
$ActionMailSMTPServer mail.example.net
$ActionMailFrom rsyslog@example.net
$ActionMailTo operator@example.net
$template mailSubject,"disk problem on %hostname%"
$template mailBody,"RSYSLOG Alert\\r\\nmsg='%msg%'"
$ActionMailSubject mailSubject
# make sure we receive a mail only once in six
# hours (21,600 seconds ;))
$ActionExecOnlyOnceEveryInterval 21600
# the if ... then ... mailBody must be on one line!
if $msg contains 'hard disk fatal failure' then :ommail:;mailBody
# re-set interval so that other actions are not affected
$ActionExecOnlyOnceEveryInterval 0

The sample below is the same, but sends mail to two recipients:

$ModLoad ommail
$ActionMailSMTPServer mail.example.net
$ActionMailFrom rsyslog@example.net
$ActionMailTo operator@example.net
$ActionMailTo admin@example.net
$template mailSubject,"disk problem on %hostname%"
$template mailBody,"RSYSLOG Alert\\r\\nmsg='%msg%'"
$ActionMailSubject mailSubject
# make sure we receive a mail only once in six
# hours (21,600 seconds ;))
$ActionExecOnlyOnceEveryInterval 21600
# the if ...  then ... mailBody mus be on one line!
if $msg contains 'hard disk fatal failure' then :ommail:;mailBody
# re-set interval so that other actions are not affected
$ActionExecOnlyOnceEveryInterval 0

A more advanced example plus a discussion on using the email feature inside a reliable system can be found in Rainer’s blogpost “Why is native email capability an advantage for a syslogd?