Thank you for the quick reply! (I was curious about the free-blocks
count too, so thanks for explaining that.) Reponses inlined:

On Tue, Feb 14, 2017 at 9:01 AM, Theodore Ts'o [off-list ref] wrote:

The way you can tell whether or not the file system has errors is to
run e2fsck -fn:

% e2fsck -fn /tmp/foo.img
e2fsck 1.43.4 (31-Jan-2017)
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Inode 15 extent tree (at level 1) could be shorter.  Fix? no

Inode 115 extent tree (at level 1) could be shorter.  Fix? no

Inode 365 extent tree (at level 1) could be shorter.  Fix? no

Inode 741 extent tree (at level 1) could be shorter.  Fix? no

Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong (6830, counted=163).
Fix? no

Free inodes count wrong (2037, counted=0).
Fix? no

/tmp/foo.img: 11/2048 files (900.0% non-contiguous), 1362/8192 blocks
% echo $?
0

If the file system has an error that needs to be fixed, it will return
an exit status of 4:

I also tested "fsck.ext4 -fn", and it returns 4 even when there is no
disk corruption. That said, doing a "fsck -E journal_only" followed by
a "fsck -fn" does seem to work:

=====

desky madthanu # fsck.ext4 -fn /dev/sdb
e2fsck 1.42.13 (17-May-2015)
Warning: skipping journal recovery because doing a read-only filesystem check.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Entry '1' in / (2) references inode 524289 in group 64 where
_INODE_UNINIT is set.
Fix? no
Entry '1' in / (2) has deleted/unused inode 524289.  Clear? no
Entry '2' in / (2) references inode 131073 in group 16 where
_INODE_UNINIT is set.
Fix? no
Entry '2' in / (2) has deleted/unused inode 131073.  Clear? no
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Inode 2 ref count is 5, should be 3.  Fix? no
Pass 5: Checking group summary information
Block bitmap differences:  -(8871--9768) -(2105376--2106287)
Fix? no
Free blocks count wrong for group #0 (23897, counted=22999).
Fix? no
Free blocks count wrong for group #64 (24544, counted=23632).
Fix? no
Free blocks count wrong (2541777, counted=2539967).
Fix? no
Inode bitmap differences:  -(12--8192)
Fix? no
Free inodes count wrong for group #0 (8181, counted=0).
Fix? no
Free inodes count wrong (655349, counted=647168).
Fix? no
/dev/sdb: ********** WARNING: Filesystem still has errors **********
/dev/sdb: 11/655360 files (0.0% non-contiguous), 79663/2621440 blocks

desky madthanu # echo $?
4

desky madthanu # fsck.ext4 -E journal_only /dev/sdb
e2fsck 1.42.13 (17-May-2015)
/dev/sdb: recovering journal

desky madthanu # echo $?
0

desky madthanu # fsck.ext4 -fn /dev/sdb
e2fsck 1.42.13 (17-May-2015)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Free blocks count wrong (2541777, counted=2412400).
Fix? no
Free inodes count wrong (655349, counted=595281).
Fix? no
/dev/sdb: 11/655360 files (136.4% non-contiguous), 79663/2621440 blocks

desky madthanu # echo $?
0

=====

Would this be the way to proceed? I am hoping "-E journal_only" also
takes care of clearing orphan inodes and still exits with a 0. (Note:
The output I pasted above is derived from a file system created with
default options, and does not switch off uninit_bg or
lazy_itable_init.)

See the fsck.ext4 man page, the "EXIT CODE" section for an explanation
for how the exit codes work.

Sorry, I did read through that, but got confused about the combination
of the exit codes and command line options.

Thanks,
Thanu