Centos – ny difference between e2fsck and e4fsck on CentOS / RHEL systems

centosext4fsckrhel

ext4.wiki.kernel.org makes it sound like e2fsck was simply renamed to e4fsck so that e4fsprogs and e2fsprogs could coexist without overlapping. However, there is no mention of any difference in the code of the command.

The e2fsck man page makes no mention of ext4, but does mention that it works with ext3 (i.e. ext2 with journaling turned on).

For Ubuntu, apparently e2fsck can handle ext2, 3 and 4 filesystems.

And of course there's good ol' vanilla fsck which itself makes no mention of ext4.

If I need to fsck an ext4 file system on a RHEL based system, which tool do I use? e4fsck? But if it's just a rename of e2fsck, can I just use that instead? Why does Ubuntu mention ext4 in its e2fsck man page but no one else seems to? And what about plain fsck on ext4?

EDIT:

On a Fedora 14 machine there is fsck.ext4, fsck.ext3 and fsck.ext2 in /sbin/. They all have the exact same file size. Curioser and Curioser.

EDIT 2:

Furthermore, when running fsck.ext4, you see that it appears to be e2fsck running. For example, I see this line when running fsck.ext4: e2fsck: aborted Tricksters!

Best Answer

e4fsprogs on RHEL5 is just a newer version of e2fsprogs. Red Hat has a policy of not upgrading to newer, binary-incompatible versions of things, so they "had to" stay on the old e2fsprogs they were using, and the solution they came up with to support ext4 was to introduce the newer version as e4fsprogs (with s/2/4/ on all of the command names). To make matters worse, ext4 support on RHEL 5 is technically a "technology preview".

I understand why they did it, but it is annoying, since you won't find e4fs* on any other distribution, including RHEL 6.

Related Solutions

What’s the difference between e2fsck and fsck and which one I should use

fsck is the original name for this tool. When new file systems came out they would need specific tools for each one. So fsck just acts as a frontend and will call the appropriate filesystem *fsck for operations that it's not able to do itself.

excerpt from the fsck man page

fs-specific-options

    Options which are not understood by fsck are passed to the 
    filesystem-specific checker.  These arguments must  not
    take  arguments,  as  there is no way for fsck to be able to 
    properly guess which arguments take options and which don't.

    Options and arguments which follow the -- are treated as file 
    system-specific options to be  passed  to  the  file
    system-specific checker.

    Please note that fsck is not designed to pass arbitrarily 
    complicated options to filesystem-specific checkers.  If
    you're doing something complicated, please just execute the 
    filesystem-specific checker  directly.   If  you  pass
    fsck  some horribly complicated option and arguments, and it 
    doesn't do what you expect, don't bother reporting it
    as a bug.  You're almost certainly doing something that you 
    shouldn't be doing with fsck.

Most of the normal operations can be handled just by fsck.

other tools?

A quick look on my Fedora 14 system shows the following fsck* tools:

$ fsck
fsck          fsck.ext2     fsck.ext4     fsck.msdos    fsck.vfat     
fsck.cramfs   fsck.ext3     fsck.ext4dev  fsck.ntfs     fsck.xfs

This locate command shows even more:

$ locate fsck|grep "^/sbin"
/sbin/dosfsck
/sbin/e2fsck
/sbin/fsck
/sbin/fsck.cramfs
/sbin/fsck.ext2
/sbin/fsck.ext3
/sbin/fsck.ext4
/sbin/fsck.ext4dev
/sbin/fsck.msdos
/sbin/fsck.ntfs
/sbin/fsck.vfat
/sbin/fsck.xfs

Between the 2 listings you can see that pretty much every file system type has its own fsck* tool. A few of the tools are multi-purpose such as dos2fsck:

$ ls -l /sbin/|grep fsck | grep dos
-rwxr-xr-x  1 root root   54424 Apr  5  2011 dosfsck
lrwxrwxrwx  1 root root       7 Aug  3  2011 fsck.msdos -> dosfsck
lrwxrwxrwx  1 root root       7 Aug  3  2011 fsck.vfat -> dosfsck

References

fsck man page

CentOS – Equivalent of ‘update-grub’ for RHEL, Fedora, and CentOS Systems

Specific actions that need to happen when a RPM package is installed or removed are included within the RPM package itself in pre-install, post-install, pre-uninstall and post-uninstall sections.

For every installed RPM package you can query the RPM database for the exact scripts that are included with the rpm command:

rpm -q --scripts <package-name>

Running that command on a kernel package for CentOS 6 returns among others:

postinstall scriptlet (using /bin/sh):
<snip>
/sbin/new-kernel-pkg --package kernel --install 2.6.32-431.17.1.el6.x86_64 || exit $?

From the manual:

new-kernel-package - tool to script kernel installation