postlog Command in Linux
The postlog command in Linux is a Postfix utility that logs the messages to the email system log. It provides a way to generate log entries with different severity levels, making it useful for debugging or custom logging in scripts.
The postlog command logs messages to syslog and, when executed in a terminal, to stderr. If text is provided, it is logged as a single entry. If no text is given, postlog reads from stdin and logs each line separately.
Table of Contents
Here is a comprehensive guide to the options available with the postlog command â
Syntax of postlog Command
The syntax of the postlog command in Linux is as follows:
postlog [options] [textâ¦]
In the above syntax, the [options] field is used to specify various options to set the priority or select the custom configuration file. The [text…] field is used to specify the message text.
Options of postlog Command
The options of the postlog command are listed below:
| Option | Description |
|---|---|
| -c config_dir | Use a specific Postfix configuration directory instead of the default. |
| -i | Include the process ID (PID) in the log tag. (Obsolete) |
| -p priority | Set the log severity: info (default), warn, error, fatal, or panic. |
| -t tag | Define a custom log tag (identifier in log entries). |
| -v | Enable verbose logging (can be repeated for more detail). |
Examples of postlog Command in Linux
This section explores how to use the Postfix postlog command in Linux with examples:
Logging a Message
To log a message, use the postlog command with the message string:
postlog "Postfix service check"
To view the logged message, use the command given below:
sudo grep "postfix" /var/log/syslog
The message has been logged as can be seen in the above output image.
Enabling Verbose Output
To enable the verbose output, use the -v option:
postlog -v "Postfix service check"
Logging a Message with a Tag
To log a message with a tag, use the -t option:
postlog -t TEST "Postfix service check"
To check the tagged message, use the following command:
sudo grep "TEST" /var/log/syslog
Logging a Warning Message
To log a warning message, use the -p option with the warn keyword:
postlog -p warn "Mail queue delay detected"
Displaying Usage Help
To display the detailed usage help of the postlog command, check its manual page:
man postlog
Conclusion
The postlog command in Linux is a useful utility in Postfix for logging messages with different severity levels. It allows logging to syslog and stderr, making it valuable for debugging and script-based logging. Various options, such as setting priority levels, adding process IDs, and defining custom tags, enhance its flexibility. The command supports logging messages directly from the command line or reading input from stdin.
In this tutorial, we explained the postlog command, its syntax, options, and usage in Linux with examples.