How to use the command 'inotifywait' (with examples)

Inotifywait is a versatile command-line utility that allows users to monitor and respond to changes within the filesystem. This command is particularly useful in environments where you need to automate processes triggered by filesystem events. By leveraging inotifywait, administrators and developers can efficiently track file modifications, accesses, and other changes, enabling them to act promptly on these events.

Watch a specific file for events, exiting after the first one

Code:

inotifywait path/to/file

Motivation:

This use case is crucial for scenarios where you need to react to the first occurrence of any change event on a particular file. It’s particularly useful if you’re testing or debugging and need a quick, one-time alert for file modifications.

Explanation:

• inotifywait: This is the base command used to monitor filesystem events.
• path/to/file: Specifies the exact file to watch for any events.

Example output:

Setting up watches.
Watches established.
path/to/file MODIFY

Continuously watch a specific file for events without exiting

Code:

inotifywait --monitor path/to/file

Motivation:

This command is ideal for ongoing monitoring of critical files where continuous scrutiny is needed. For example, in system logs or configuration files, constant vigilance can prevent issues from going unnoticed.

Explanation:

• --monitor: This argument tells inotifywait to keep watching the specified file indefinitely, reporting events as they happen.
• path/to/file: Indicates the file to be monitored continuously.

Example output:

Setting up watches.
Watches established.
path/to/file MODIFY
path/to/file MODIFY

Watch a directory recursively for events

Code:

inotifywait --monitor --recursive path/to/directory

Motivation:

Sometimes, changes could occur across multiple files within a directory structure. By using this command, you can observe any modifications in the given directory and all its subdirectories, which is useful for overseeing project folders or large datasets.

Explanation:

• --monitor: Enables continuous watching.
• --recursive: Monitors all files within the directory and its subdirectories.
• path/to/directory: Specifies the directory to be monitored.

Example output:

Setting up watches.
Watches established.
path/to/directory/file1 CREATE
path/to/directory/subdir/file2 MODIFY

Watch a directory for changes, excluding files, whose names match a regular expression

Code:

inotifywait --monitor --recursive --exclude "regular_expression" path/to/directory

Motivation:

When monitoring a directory, there may be certain files you don’t want to watch, perhaps due to their frequency of change or because they contain unimportant data. This command allows you to filter out those files using a regular expression.

Explanation:

• --monitor: Continues monitoring without stopping.
• --recursive: Watches the specified directory and all its subdirectories.
• --exclude "regular_expression": Excludes from monitoring any files that match the given regular expression pattern.
• path/to/directory: The directory to be observed.

Example output:

Setting up watches.
Watches established.
path/to/directory/important_file MODIFY

Watch a file for changes, exiting when no event occurs for 30 seconds

Code:

inotifywait --monitor --timeout 30 path/to/file

Motivation:

This scenario is beneficial when you want to monitor a file but automatically stop if no changes happen within a set timeframe. This is useful when resources are limited, and you need to free them up if no immediate changes are detected.

Explanation:

• --monitor: Keeps watching until the timeout is reached.
• --timeout 30: Stops monitoring after 30 seconds of inactivity.
• path/to/file: The file you wish to monitor for changes.

Example output:

Setting up watches.
Watches established.
<30 seconds pass, no output if no changes>

Only watch a file for file modification events

Code:

inotifywait --event modify path/to/file

Motivation:

There are situations where only modification events are important, such as a log file with expected changes where you don’t want alerts for accesses or attribute changes. This command ensures you receive notifications solely for modifications.

Explanation:

• --event modify: Limits the monitoring to modification events, ignoring other types of access or changes.
• path/to/file: The file to be monitored.

Example output:

Setting up watches.
Watches established.
path/to/file MODIFY

Watch a file printing only events, and no status messages

Code:

inotifywait --quiet path/to/file

Motivation:

Sometimes, you may prefer minimal output for cleaner logs or scripts, where only the actual events are needed without setup status messages cluttering the output.

Explanation:

• --quiet: Suppresses startup messages and only outputs when an event occurs.
• path/to/file: The file that will be monitored for events.

Example output:

path/to/file MODIFY

Run a command when a file is accessed

Code:

inotifywait --event access path/to/file && command

Motivation:

Executing a command in response to a file access event can be useful for automated jobs, such as refreshing a cache or logging usage metrics whenever a particular file is accessed.

Explanation:

• --event access: Watches for file access events.
• path/to/file: The file to monitor for access.
• && command: Specifies the command to execute when the access event occurs.

Example output:

Assuming command is echo "File accessed":

Setting up watches.
Watches established.
path/to/file ACCESS
File accessed

Conclusion:

The inotifywait command provides a wealth of functionalities that are essential for any situation requiring automatic and responsive file or directory monitoring. By using various options, users can tailor it to suit precise workflow requirements, whether for single-file monitoring or complex recursive directory checks. Understanding and applying inotifywait can significantly automate and streamline file management tasks across various scenarios.