When an application reads a file, Linux kernel keeps cache of file contents in memory. The Linux keeps the cache even after application closes the file to improve performance for further read operations of same file. This cache is freed slowly as when Linux finds no free memory during it operation.

Similarly when an application write a file, Linux doesn’t write the contents to disk immediately and waits for some time before it actually writes to the disk. These buffers are called dirty buffers.

User can manually initiate the writing of dirty buffers to disk executing “sync” command few times.

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