Newbie question about mkfs.xfs command

What does the second "loop" means in "mkfs.xfs -d file=loop loop"? Thanks.

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The final parameter to mkfs.xfs needs to be a block device or a file.

In your case it looks like you intend to create a filesystem on a file called loop (so you can mount it later as a loopback device?).

You dont need the '-d file=loop' (which is invalid, file= takes 1 or 0), mkfs.xfs usually figures this out.

So assuming you created a test file with something like

# dd if=/dev/zero of=testfile bs=1k count=100000
100000+0 records in
100000+0 records out
102400000 bytes (102 MB) copied, 0.770193 seconds, 133 MB/s

You make an xfs filesystem with just

# mkfs.xfs testfile
meta-data=bar                    isize=256    agcount=6, agsize=4096 blks
         =                       sectsz=512   attr=0
data     =                       bsize=4096   blocks=24576, imaxpct=25
         =                       sunit=0      swidth=0 blks, unwritten=1
naming   =version 2              bsize=4096
log      =internal log           bsize=4096   blocks=1200, version=1
         =                       sectsz=512   sunit=0 blks, lazy-count=0
realtime =none                   extsz=4096   blocks=0, rtextents=0

And after making a mount point, mount it with

# mount -o loop testfile testmount

The -o loop tells mount to use a loopback device to turn your testfile into a block device for the mount. This is the only step you need root permissions for.

Don