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Abstract

A method for deleting files on a UNIX file system, so that they may subsequently be undeleted, without any possibility of loss or damage. A file deleted with the 'rm' command, or targeted by the 'cp' or 'mv' commands, is deleted simply by marking its directory record 'deleted', while its inode and data blocks are not freed. The 'ls' command is adjusted so as not to display files whose directory records are marked as deleted. A indexed system of deleted-file records of such deleted files is maintained by the UNIX kernel, such that a record for each deleted file contains a pointer to the file's inode, a pointer to the file's directory inode, and the file's deletion time. A deleted file may be undeleted simply by calling an 'unrm ' command, which uses a kernel system call to undo 'deleted' mark in the file's directory record. This procedure restores the file completely, because its inode and data blocks were never freed. The 'ls' command again will display the file. The indexed system of deleted-file records, created over time as files are deleted from the UNIX file system, is a necessary tool used by the kernel to efficiently remove the oldest deleted files from the system automatically, without excess system overhead, and without cumbersome system maintenance procedures required from the system administrator.

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