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174 changes: 105 additions & 69 deletions docs/guides/email/postfix_reporting.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,5 @@
---
title: Postfix Process Reporting
title: Using `postfix` for Process Reporting
author: Steven Spencer
contributors: Ezequiel Bruni, Ganna Zhyrnova
tested_with: 8.5, 8.6, 9.0
Expand All @@ -9,8 +9,6 @@ tags:
- tools
---

# Using `postfix` for server process reporting

## Prerequisites

- Complete comfort operating from the command line on a Rocky Linux server
Expand All @@ -21,63 +19,65 @@ tags:

## Introduction

Many Rocky Linux server administrators write scripts to perform specific tasks, like backups or file synchronization, and many of these scripts generate logs that have useful and sometimes very important information. Just having the logs, though, is not enough. If a process fails and logs that failure, but the busy administrator does not review the log, then a catastrophe could be in the making.
Many Rocky Linux server administrators write scripts to perform specific tasks, such as backups or file synchronization, and many of these scripts generate logs that have useful and sometimes very important information. Just having the logs, though, is not enough. If a process fails and logs that failure, but the busy administrator does not review the log, then a catastrophe could be in the making.

This document shows you how to use the `postfix` MTA (mail transfer agent) to grab log details from a particular process, and send them to you via email. It also touches on date formats in logs, and helps you identify which format you need to use in the reporting procedure.
This document shows you how to use the `postfix` MTA (mail transfer agent) to grab log details from a particular process, and send them to you by email. It also touches on date formats in logs, and helps you identify the format you need to use in the reporting procedure.

Remember, this is just the tip of the iceberg regarding what you can do with reporting via `postfix`. Note that it is always a good security move to limit running processes to only those you will need all the time.

This document shows you how to enable postfix only for the reporting you need it to do, and then shut it down again.

## `postfix` defined

`postfix` is a server daemon used for sending email. It is more secure and simpler than sendmail, another MTA that was the default go-to MTA for years. You can use it as part of a full-featured mail server.
`postfix` is a server daemon used for sending email. It is more secure and simpler than `sendmail`, another MTA that was the default go-to MTA for years. You can use it as part of a full-featured mail server.

## Installing `postfix`

Aside from `postfix`, you will need `mailx` to test your ability to send emails. To install these and any dependencies required, enter the following on the Rocky Linux server command line:

`dnf install postfix mailx`

!!! warning "Rocky Linux 9.0 Changes"

This procedure works perfectly fine in Rocky Linux 9.0. The difference here is where the `mailx` command comes from. While you can install it by name in 8.x, `mailx` comes from the appstream package `s-nail` in 9.0. To install the needed packages, you need to use:
Aside from `postfix`, you will need `s-nail` to test your ability to send emails. To install these and any dependencies required, enter the following on the Rocky Linux server command line:

```
dnf install postfix s-nail
```
```bash
dnf install postfix s-nail
```

## Testing and configuring `postfix`

### Testing mail first

Before you configure `postfix`, you need to find out how mail will look when it leaves the server, as you will probably want to change this. To do this, start `postfix`:
Before you configure `postfix`, you need to discover how mail will look when it leaves the server, as you will probably want to change this. To do this, start `postfix`:

`systemctl start postfix`
```bash
systemctl start postfix
```

Test with the `mail` provided by `mailx` (or `s-nail`):
Test with the `mail` provided by `s-nail`:

`mail -s "Testing from server" myname@mydomain.com`
```bash
mail -s "Testing from server" myname@mydomain.com
```

This will display a blank line. Type your testing message in here:

`testing from the server`

Hit enter, and enter a single period:
```bash
testing from the server
```

`.`
Hit ++enter++, and then a single ++period++:

The system will respond with the following:

`EOT`
```bash
EOT
```

The purpose for doing this is to see how our mail looks to the outside world. You can get a feel for this from the _maillog_ that goes active with the starting of `postfix`.
The purpose for doing this is to see how your mail looks to the outside world. You can get a feel for this from the `maillog` that goes active with the starting of `postfix`.

Use this command to see the output of the log file:

`tail /var/log/maillog`
```bash
tail /var/log/maillog
```

You will see something like this, although the log file will have different domains for the email address, and other items:
You will see something similar to this, although the log file will have different domains for the email address, and other items:

```bash
Mar 4 16:51:40 hedgehogct postfix/postfix-script[735]: starting the Postfix mail system
Expand All @@ -93,100 +93,128 @@ Mar 4 16:52:06 hedgehogct postfix/qmgr[739]: C9D42EC0ADD: removed

The "somehost.localdomain" shows that you need to make some changes. Stop the `postfix` daemon first:

`systemctl stop postfix`
```bash
systemctl stop postfix
```

## Configuring `postfix`

Since you are not setting up a complete, fully functional mail server, the configuration options that you will use are not as extensive. The first thing to do is to modify the _main.cf_ file (literally the main configuration file for `postfix`). Make a backup first:
Since you are not setting up a complete, fully functional mail server, the configuration options that you will use are not as extensive. The first thing to do is to change the `main.cf` file (literally the main configuration file for `postfix`). Make a backup first:

`cp /etc/postfix/main.cf /etc/postfix/main.cf.bak`
```bash
cp /etc/postfix/main.cf /etc/postfix/main.cf.bak
```

Edit it:

`vi /etc/postfix/main.cf`
```bash
vi /etc/postfix/main.cf
```

In our example, our server name is "bruno" and our domain name is "ourdomain.com". Find the line in the file:
In this example, your server name is "bruno" and your domain name is "ourdomain.com". Find the line in the file:

`#myhostname = host.domain.tld`
```bash
#myhostname = host.domain.tld
```

You can remove the remark (#) or add a line under this line. Based on our example, the line will read:
You can remove the remark (#) or add a line under this line. Based on the example, the line will read:

`myhostname = bruno.ourdomain.com`
```bash
myhostname = bruno.ourdomain.com
```

Next, find the line for the domain name:

`#mydomain = domain.tld`
```bash
#mydomain = domain.tld
```

Again, remove the remark and change it, or add a line under it:

`mydomain = ourdomain.com`
```bash
mydomain = ourdomain.com
```

Finally, go to the bottom of the file and add this line:

`smtp_generic_maps = hash:/etc/postfix/generic`
```bash
smtp_generic_maps = hash:/etc/postfix/generic
```

Save your changes (in `vi` it is `Shift : wq!`) and exit the file.
Save your changes and exit the file.

Before you continue editing the generic file, you need to see how the email will look. Specifically, you want to create the "generic" file that you referenced in the _main.cf_ file above:
Before you continue editing the generic file, you need to see how the email will look. Specifically, you want to create the "generic" file that you referenced in the `main.cf` file earlier:

`vi /etc/postfix/generic`
```bash
vi /etc/postfix/generic
```

This file tells `postfix` how any email coming from this server will look. Remember our test email and the log file? This is where we fix all of that:
This file tells `postfix` how any email coming from this server will look. Remember your test email and the log file? This is where you fix all of that:

```bash
root@somehost.localdomain root@bruno.ourdomain.com
@somehost.localdomain root@bruno.ourdomain.com
```

Next, you need to tell `postfix` to use all of our changes. Do this with the postmap command:
Next, you need to tell `postfix` to use all of your changes. Do this with the `postmap` command:

`postmap /etc/postfix/generic`
```bash
postmap /etc/postfix/generic
```

Start `postfix` and test your email again with the same procedure used above. You will now see that all "localdomain" instances are now the actual domain.
Start `postfix` and test your email again with the same procedure used earlier. You will now see that all "localdomain" instances are now the actual domain.

### The `date` command and a variable called today

Not every application will use the same logging format for the date. You might have to get creative with any script you write for reporting by date.

Say that you want to see your system log as an example and pull everything that has to do with dbus-daemon for today's date, and email it to yourself. (It is probably not the greatest example, but it will give you an idea of how you might do this.)
Say that you want to see your system log as an example and pull everything that has to do with `dbus-daemon` for today's date, and email it to yourself. (It is probably not the greatest example, but it will give you an idea of how you do this.)

You need to use a variable in your script. Call it "today". You want it to relate to output from the "date" command and format it in a specific way, so that you can get the data you need from our system log (in _/var/log/messages_). To start with, do some investigative work.
You need to use a variable in your script. Call it "today". You want it to relate to output from the "date" command and format it in a specific way, so that you can get the data you need from your system log (in `/var/log/messages`). To start with, do some investigative work.

First, enter the date command in the command line:

`date`
```bash
date
```

This will give you the default system date output, which might be something like this:
This shows you the default system date output, which might be similar to this:

`Thu Mar 4 18:52:28 UTC 2021`
```bash
Thu Mar 4 18:52:28 UTC 2021
```

Check our system log and see how it records information. To do this, use the `more` and `grep` commands:
Check your system log and see how it records information. To do this, use the `more` and `grep` commands:

`more /var/log/messages | grep dbus-daemon`
```bash
more /var/log/messages | grep dbus-daemon
```

Which will give you something like this:
Which will give you something similar to this:

```bash
Mar 4 18:23:53 hedgehogct dbus-daemon[60]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher'
Mar 4 18:50:41 hedgehogct dbus-daemon[60]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service' requested by ':1.1' (uid=0 pid=61 comm="/usr/sbin/NetworkManager --no-daemon " label="unconfined")
Mar 4 18:50:41 hedgehogct dbus-daemon[60]: [system] Successfully activated service 'org.freedesktop.nm_dispatcher
```

The date and log outputs need to be exactly the same in our script. Let us see how to format the date with a variable called "today".
The date and log outputs need to be exactly the same in your script. Let us see how to format the date with a variable called "today".

Examine what you need to do with the date to get the same output as the system log. You can reference the [Linux man page](https://man7.org/linux/man-pages/man1/date.1.html) or type `man date` on the command line to pull up the date manual page to get the information you need.

What you will find is to format the date the same way as _/var/log/messages_ , you need to use the %b and %e format strings, with %b being the 3 character month and %e being the space-padded day.

### The script

For our bash script, you can see that you are going to use the `date` command and a variable called "today". (Remember that "today" is arbitrary. You can call this variable anything you like). You will call your script in this example, `test.sh` and place it in _/usr/local/sbin_:
For your bash script, you can see that you are going to use the `date` command and a variable called "today". (Remember that "today" is arbitrary. You can call this variable anything). You will call your script in this example, `test.sh` and place it in `/usr/local/sbin`:

`vi /usr/local/sbin/test.sh`
```bash
vi /usr/local/sbin/test.sh
```

At the beginning, notice that even though the comment in our file says you are sending these messages to email, for now, you are just sending them to a standard log output to verify that they are correct.
At the beginning, notice that even though the comment in the file says you are sending these messages to email, for now, you are just sending them to a standard log output to verify that they are correct.

Also, in our first run of the script, you are grabbing all of the messages for the current date not just the dbus-daemon messages. You will deal with that shortly.
Also, in your first run of the script, you are grabbing all the messages for the current date not just the `dbus-daemon` messages. You will deal with that shortly.

Be aware that the `grep` command will return the filename in the output, which you will not want in this case. To remove this, add the "-h" option to grep. In addition, when you set the variable "today", you need to look for the entire variable as a string, which needs the string within quotes:

Expand All @@ -200,17 +228,23 @@ today=`date +"%b %e"`
grep -h "$today" /var/log/messages
```

That is it for now. Save your changes and make the script executable:
That is it. Save your changes and make the script executable:

`chmod +x /usr/local/sbin/test.sh`
```bash
chmod +x /usr/local/sbin/test.sh
```

Test it:

`/usr/local/sbin/test.sh`
```bash
/usr/local/sbin/test.sh
```

If all works correctly, you will get a long list of all of the messages in _/var/log/messages_ from today, including but not limited to the dbus-daemon messages. The next step is to limit the messages to the dbus-daemon messages. Change your script again:
If all works correctly, you will get a long list of all of the messages in `/var/log/messages` from today, including but not limited to the `dbus-daemon` messages. The next step is to limit the messages to the dbus-daemon messages. Change your script again:

`vi /usr/local/sbin/test.sh`
```bash
vi /usr/local/sbin/test.sh
```

```bash
#!/bin/bash
Expand All @@ -222,11 +256,13 @@ today=`date +"%b %e"`
grep -h "$today" /var/log/messages | grep dbus-daemon
```

Running the script again, will get you only the dbus-daemon messages and only the ones that occurred today.
Running the script again, will get you only the `dbus-daemon` messages and only the ones that occurred today.

One final step remains. Remember, you need to get this emailed to the administrator for review. Because you are only using `postfix` on this server for reporting, you do not want to leave the service running. Start it at the beginning of the script and stop it at the end. Here, the `sleep` command pauses for 20 seconds, ensuring sending the email before shutting `postfix` down again. This final edit, adds the stop, start, and sleep issues just discussed, and also pipes the content to the administrator's email.
There is one final step. Remember, you need to get this emailed to the administrator for review. Because you are only using `postfix` on this server for reporting, you do not want to leave the service running. Start it at the beginning of the script and stop it at the end. Here, the `sleep` command pauses for 20 seconds, ensuring sending the email before shutting `postfix` down again. This final edit, adds the stop, start, and sleep issues just discussed, and also pipes the content to the administrator's email.

`vi /usr/local/sbin/test.sh`
```bash
vi /usr/local/sbin/test.sh
```

Change the script:

Expand All @@ -249,10 +285,10 @@ sleep 20
/usr/bin/systemctl stop postfix
```

Run the script again, and you will now have an email from the server with the dbus-daemon message.
Run the script again, and you will now have an email from the server with the `dbus-daemon` message.

You can now use [a crontab](../automation/cron_jobs_howto.md) to schedule this to run at a specific time.

## Conclusion

Using `postfix` can help you keep track of process logs that you want to monitor. You can use it along with bash scripting to gain a firm grasp of your system processes and be informed if there is trouble.
Using `postfix` can help you keep track of process logs that you want to monitor. You can use it along with bash scripting to gain a firm grasp of your system processes and have that information emailed to you if there is trouble.