The logger command is a versatile tool used in Unix-like operating systems to send messages to the system log (commonly managed by syslogd or rsyslogd). It enables users, scripts, and applications to log custom messages, making it an essential utility for debugging, monitoring, and system administration.
Key Features
- Sends Messages to the System Log: The primary function of
loggeris to write messages to the system log, which can be accessed via log files like/var/log/syslog,/var/log/messages, or custom locations defined in the syslog configuration. - Customizable Logging Options: It allows specifying log levels, facilities, and tags to categorize and filter messages efficiently.
- Script Integration: Integrates seamlessly into scripts to provide contextual logging for automation or error tracking.
Basic Syntax
logger [options] [message]
[message]: The message to log. If no message is provided,loggerreads input from standard input.
Common Options
| Option | Description |
|---|---|
-p priority | Sets the log priority (facility.level). Example: user.info, auth.error. |
-t tag | Adds a tag to the log message, typically the name of the application or script. |
-i | Includes the process ID (PID) of the logger command in the log message. |
-f file | Logs the content of the specified file. |
--stderr | Outputs the message to standard error as well as the system log. |
--id | Appends a numerical identifier to the message. |
Examples
1. Log a Simple Message
logger "System maintenance scheduled at midnight."
- This logs a simple message, viewable in
/var/log/syslogor equivalent.
2. Log with a Custom Tag
logger -t "CRON" "Daily backup job completed."
- Adds the tag
CRONto the log entry for easier identification.
3. Log with a Specific Priority
logger -p auth.warning "Failed login attempt detected."
- Logs a message with the facility
authand levelwarning.
4. Log File Contents
logger -f /var/log/error_log
- Reads and logs the contents of the specified file.
5. Log with PID
logger -i "Application started successfully."
- Logs the message and includes the process ID of
logger.
6. Use Logger in a Script
#!/bin/bash
logger -t "BackupScript" "Backup job started."
# Backup command
logger -t "BackupScript" "Backup job completed."
- Logs messages to track the progress of a backup script.
System Log Context and Benefits of Using logger
The logger command integrates with the system log, organizing messages based on facilities and severity levels. Understanding these classifications can help in effectively managing and analyzing log data. Additionally, the logger command offers several benefits, especially for system administrators and developers.
System Log Context
| Aspect | Details |
|---|---|
| Facilities | Categories that group log messages, such as auth, cron, user, daemon, kern, etc. |
| Levels | Severity levels that indicate the importance of a log message: |
– debug: Debugging information | |
– info: General informational messages | |
– notice: Normal but significant events | |
– warning: Warnings about potential issues | |
– err: Non-critical errors | |
– crit: Critical issues | |
– alert: Immediate attention required | |
– emerg: Emergency situations | |
| Combination | The combination of facilities and levels (e.g., auth.warning) determines how and where the message is logged, based on syslog configuration. |
Benefits of Using logger
| Benefit | Description |
|---|---|
| Centralized Logging | Ensures all logs are stored in a unified location, simplifying management and analysis. |
| Enhanced Troubleshooting | Helps identify issues quickly by allowing logs to be tagged and categorized effectively. |
| Automation-Friendly | Integrates seamlessly into scripts, enabling contextual logging and easier debugging in automated workflows. |
By leveraging the structured organization of system logs and the features of the logger command, users can ensure efficient logging and monitoring for a wide range of applications.
The logger command is a lightweight yet powerful tool for integrating custom messages into the system log. By leveraging its options, you can organize, filter, and analyze logs effectively, making it invaluable for maintaining robust system operations.