SCO Unix ® FAQ section

This article is from a FAQ concerning SCO operating

Unix, Xenix and ODT General FAQ

Is rm final? Are the files gone forever?

Depends on what you mean by really gone and also depends upon your file system, your OS, and rm itself.

First: traditional Unix:

When you rm a file all that happens is that the directory entry is set to point at 0 instead of the inode it did point at, and the link count for the inode is decremented by one. If the link count has reached 0, and no process has the file open, then the inode itself is marked us unused, and the disk blocks that the file used are returned to the free list. If a process has the file open then the release of the inode and the reclaim of disk blocks waits until the process is done.

So, at this point, your data is still there until some other process needs disk blocks and these happen to get reused. If nothing asks for new blocks, or these blocks get put at the end of the free list, you might be able to recover the data by scrounging through the free list.

Secure Unix systems may zero disk blocks before releasing them to the free list; you wouldn't have any way to get your data if that was in effect.

Now: Some file systems have various schemes to keep "versions" of your data or to provide an undelete feature. In that case, older copies of your data may still be there. However, even if your file system supports something like that, it may not be turned on by default: see Does SCO OpenServer5 support the 'undelete' feature? (file system versioning) for example.

Linux ext2 file systems document an undelete in chattr but it isn't actually implemented at all.

Some systems mess with rm either by an alias or a binary to store the "deleted" file somewhere safe for a while.

See Shred and plug "undelete" into the Search box at the top of the page for more.

Just in case some Windows Vista user stumbled in: Recover Files with Shadow Copies on Any Version of Windows Vista

Windows 7 has real undelete: Recover lost or deleted files.

Newer Ubuntu has more help, too: Ubuntu DataRecovery.

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