backup_file has different perms because you copied the file to a new file as a different user. I am not saying backup_file is gone if you hit that case -- only that you end up in a situation where your app or the other apps that use that file are looking at corrupt data (they don't know about backup_file). cat backup_file > file does the following: 
trunc file.

# this is where you have the race condition.

redirects the data in backup_file to file.  
closes file

[download]


-Waswas

In reply to Re^6: Writing to a file atomically without renaming by waswas-fng
in thread Writing to a file atomically without renaming by nomis80

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