fincore

Display cache details for a file

$ fincore [path/to/file]

$ fincore --output-all [path/to/file]

$ fincore [[-h|--help]]

fincore [options] file...

-p, --pages
    Print the list of pages in core.

-b, --bytes
    Print the number of bytes in core, instead of percentage.

-q, --quiet
    Do not print the file header.

-z, --zeros
    Count zeroed pages in core.

-n, --no-summary
    Do not print the summary (total number of bytes in core).

-o OFFSET
    Start at the given offset.

-l LENGTH
    Stop after LENGTH bytes.

-m, --merge
    Merge multiple files into one output (for pages view).

-v, --version
    Display version information and exit.

-h, --help
    Display help text and exit.

file...
    One or more files to examine. Standard input is also accepted.

The `fincore` command is a Linux utility that reports how much of a specified file's data is currently cached in the system's page cache (RAM). It provides insights into file access patterns and I/O performance. By analyzing which parts of a file are actively in memory, administrators can optimize disk I/O, identify performance bottlenecks, and better understand the caching behavior of their applications. The command can be used on single files, multiple files, or the standard input. The output displays the fraction of each file's contents residing in the page cache. `fincore` helps in scenarios where fast access to specific files is critical, such as database operations or high-performance computing. It gives administrators a tool to make informed decisions about resource allocation and data placement to improve overall system efficiency.

The results of `fincore` are a snapshot in time. The page cache is dynamic, and pages can be evicted or added at any moment. Therefore, repeated executions of `fincore` might produce different results.

The output indicates the percentage (or number of bytes, if using `-b`) of the specified file that resides in the page cache. A higher percentage implies more data is readily available in RAM, potentially leading to faster access times.
Example:
`fincore myfile.txt`
might output:
`myfile.txt: 50%`
This means that 50% of `myfile.txt` is currently in the page cache.

Common use cases for `fincore` include:

• Performance Tuning: Identify frequently accessed files that should be kept in memory.
• Diagnosing I/O Bottlenecks: Determine if disk I/O is a limiting factor in application performance.
• Cache Management: Monitor the effectiveness of caching strategies.

vmstat(8), free(1), ps(1)