This is historical behavior of mkfs.ext[234]; it was added only fairly recently in 1.42.10, and RHEL7 ships 1.42.9.  As such, this is more of an RFE than a bug.

commit dbcd617882ee5c9da80d9257475f2594352f6698
Author: Theodore Ts'o <tytso>
Date:   Sat Apr 26 18:42:31 2014 -0400

    mke2fs: check for pre-existing file system
    
    Warn the system administrator if there is an existing file system on
    the block device, and give the administrator an opportunity to abort
    the mkfs operation.
    
    Signed-off-by: "Theodore Ts'o" <tytso>


I have some concern about adding this, because it changes the expected behavior as shipped in RHEL7 GA.

However, the upstream patch does try to address this problem:

        /* The isatty() test is so we don't break existing scripts */
        flags = CREATE_FILE;
        if (isatty(0) && isatty(1))
                flags |= CHECK_FS_EXIST;

so it may be acceptable.

Hi Eric,
Yes, from RHEL point of view it is more a RFE than a bug report.
Anyway, the test for tty should address any concern about problems for scripts so, please, consider it very seriously for inclusion (if it is possible, obviously). 

Heck, to tell the truth, I would prefer that scripts _fail_ rather than silently delete potentially delete valuable data - but I absolutely understand your reluctantly to such a drastic change.

The other thing, of course, is muscle memory - I now reflexively type "mkfs.xfs -f" every time I invoke it, so it's not much of a barrier to disaster ...

-Eric

Mmm... This really depends... I (unfortunately) learned the hard way that forced operation on destructive command (mkfs, rm, etc.) should be given only if absolutely needed. In other words, I use mkfs.xfs -f very carefully :)

While upstream has added this, I'm not going to make the change in RHEL7.  People expect stable behavior in RHEL, and this would be a very user-visible change; some people may prefer it, others may not.

ext2/3/4 has gone without the warning for more than a decade.

New releases of RHEL will have the new behavior, but I'm not going to change it in RHEL7.

Please reconsider that. Destroying user data *without warnings* is a very bad thing.

Let me describe another scenario: to be checked for errors, an ext4 filesystem must be unmounted. Now, with an unmounted fiesystem, if the user naively (stupidly?) type the wrong command, exchanging 'fsck.ext4' with 'mkfs.ext4' it will *lose all data*

I understand that an user writing a wrong command should blame himself. However, we are humans an errors happens sometime - but they are much more dangerous if the system blindly obey without even raising some warning.

The proposed solution (to complain only when connected to a TTY), would fix the problem without impairing any unattended scripts, so it seems a relatively safe change.

Anyway, thank you for your time.
Regards.

I wonder what happened with this one? I'm trying it out in a script in RHEL 9 and it still destroys data by default. 

Any news?