LinuxQuestions.org - preventing deletion of an opened file

- Programming (https://www.linuxquestions.org/questions/programming-9/)

- - preventing deletion of an opened file (https://www.linuxquestions.org/questions/programming-9/preventing-deletion-of-an-opened-file-525694/)

preventing deletion of an opened file

Hi everybody,

Is it possible to prevent a file from deletion, if that file is opened by a process ?

All operations are performed by "root".

rw------- foo.bin

processA opened "foo.bin"

I want "rm foo.bin" can not delete this file.

The only way mandatory locking ?

TIA

If you're worried about the program failing because the blocks on disk might get removed while it's running, don't. On unix-like systems file data is only purged from disk when the link count reaches 0. Having a file in a directory raises the link count by one. So does having an open file handle for that file. While the program is running, even if the file is removed from the directory where it exists, the link count will still not drop to 0 because there is an open file handle for that file. Only when the program finishes and the file handle to the file is closed will the data be removed from the disk.

If you simply want to stop people removing the file from the directory, just change the permissions:

Code:

chmod a-w foo.bin

Note that removing a file from a directory actually only requires write permission to the directory in which it lives, but AFAIK, most programs will refuse to remove a file with no write permission, or at least warn you about it:

Code:

matthew@chubby:~/tmp$ touch testfile

matthew@chubby:~/tmp$ chmod a-w testfile

matthew@chubby:~/tmp$ ls -l testfile

-r--r--r-- 1 matthew matthew 0 2007-02-05 09:54 testfile

matthew@chubby:~/tmp$ rm testfile

rm: remove write-protected regular empty file `testfile'? n

...although note that the -f (force) option stops this warning:

Code:

matthew@chubby:~/tmp$ rm -f testfile

matthew@chubby:~/tmp$ ls -l testfile

ls: testfile: No such file or directory

In fact, the problem is

processA continuously writes some kind of log to "foo.bin". If you remove file, processA does'nt know it. And write system call does'nt give any error although when you look at /proc/<pid>/fd, the file has (deleted) info near its name. You can use inotify maybe to close/re-open again that file to continue to logging. Or prevent totally the deletion of this log file. Since flock is an advisory lock, it does'nt work.

Thanks

Try
chattr -i file

Also, if you get the file creator ie logging prog to immediately unlink (delete) the file after opening it, it will be invisible to other cmds (I think).
This is often used to create temp files that can't be interfered with by other processes.