How to Use the Command 'multitail' (with examples)

The multitail command is an advanced tool that extends the functionality of the traditional Unix tail command. It is specifically designed to help users track log files and other text file updates in real time. By allowing multiple files to be displayed in separate or merged windows, multitail provides a dynamic and flexible approach for monitoring logs across multiple files and directories concurrently. This tool is particularly useful for system administrators and developers who need to keep an eye on real-time data streams, like server logs, across various files simultaneously.

Use case 1: Tail all files matching a pattern in a single stream

Code:

multitail -Q 1 'pattern'

Motivation:

In environments where log files are generated frequently and organized in a way that can be matched with a specific pattern, monitoring all those logs in real time becomes crucial. This use case allows users to consolidate and monitor updates across multiple logs that fit a defined criterion, improving efficiency and ensuring no relevant information is missed.

Explanation:

• -Q: This flag is used to specify a query for filtering files. It will match any file whose name contains the specified pattern.
• 1: The number following the -Q tells multitail to merge all matching files into a single output stream, thereby making it easier for the user to monitor them collectively.
• 'pattern': This represents the regex pattern to match the files. You replace ‘pattern’ with your specific criteria to match files by name.

Example output:

==> log_file1.log <==
{"time":"2023-10-01T12:00:00", "event":"start", "user":"user1"}
==> log_file2.log <==
{"time":"2023-10-01T12:00:02", "event":"process", "user":"user2"}
==> log_file3.log <==
{"time":"2023-10-01T12:00:05", "event":"end", "user":"user1"}

Use case 2: Tail all files in a directory in a single stream

Code:

multitail -Q 1 'path/to/directory/*'

Motivation:

When managing a system with numerous log files stored in a single directory, it can be challenging to individually monitor each log. This command simplifies the process by combining them into a single stream, allowing for immediate, consolidated insights into all log files within the directory.

Explanation:

• -Q: This flag, as before, is used to filter files, but in this case, it’s applied to an entire directory.
• 1: Again, this number indicates that all matched files will be merged into a single output stream.
• 'path/to/directory/*': This specifies the directory and matches all files within it using the wildcard ‘*’, ensuring comprehensive monitoring.

Example output:

==> /log/directory/log1.txt <==
Entry from log1
==> /log/directory/log2.txt <==
Entry from log2
==> /log/directory/log3.txt <==
Entry from log3

Use case 3: Automatically add new files to a window

Code:

multitail -Q pattern

Motivation:

In continuously operational systems, new log files are often generated and require real-time oversight. This command automatically incorporates newly created files that match a certain pattern into an existing multitail window, thus maintaining uninterrupted monitoring without manual updates.

Explanation:

• -Q: This is used to specify a matching pattern.
• pattern: Describes the naming pattern for new files that should be included upon their creation. No numeric parameter ensures new matching files are displayed in a new window, not yet merged.

Example output:

==> /logs/file_initial.log <==
log entry

[NEW FILE ADDED]

==> /logs/file_new.log <==
new log entry

Use case 4: Show 5 logfiles while merging 2 and put them in 2 columns with only one in the left column

Code:

multitail -s 2 -sn 1,3 path/to/mergefile -I path/to/file1 path/to/file2 path/to/file3 path/to/file4

Motivation:

For complex monitoring situations where numerous logs need to be correlated, arranging several log files side-by-side can enhance readability and contextual understanding, particularly when some logs should be merged due to their interdependencies.

Explanation:

• -s 2: Specifies that the display layout should have two columns.
• -sn 1,3: This arranges a specific format for columns where only the third entry (file/page) from the list goes into the left column.
• path/to/mergefile: This indicates the file whose contents are to be merged together when monitored.
• -I: This option is used to include additional separate files in the display.
• path/to/file1 path/to/file2 path/to/file3 path/to/file4: These paths specify the additional logs to be monitored, with file3 set to appear in its separate column view.

Example output:

Column 1                | Column 2
------------------------|------------------------
                        | ==> /logs/mergefile1 <==
                        | Merge log content
                        |
==> /logs/file1.log <== |
==> /logs/file2.log <== |
==> /logs/file4.log <== |

Conclusion:

multitail serves as a powerful utility for monitoring multiple log files simultaneously, offering diverse functionalities that cater to a range of log monitoring needs. Whether you’re consolidating real-time file updates, tracking the latest additions to folders, or orchestrating a structured view across several streams, multitail enhances efficiency and ensures comprehensive oversight in a dynamic computing environment.