Sometimes you may need additional local partition or local mountable drives, but you dont have free blocks in the parition table. In that case virtual filesystem helps. You can create a virtual filesystem and mount them as a loopback device. Here are the steps to do it.

  1. Create a empty file with the mount of disk space you need. Here I have created a 1G file.

    [root@unixfoo23 ~]# dd if=/dev/zero of=/root/myfs1 bs=1024 count=1048576
    1048576+0 records in
    1048576+0 records out

    [root@unixfoo23 ~]# ls -l /root/myfs1
    -rw-r–r–  1 root root 1073741824 Jun 25 08:32 /root/myfs1

    [root@unixfoo23 ~]# du -sh /root/myfs1
    1.1G    /root/myfs1
    [root@unixfoo23 ~]#

  2. Create a filesystem on the virtual device (/root/myfs1). I have selected ext3 , whereas you can create the filesystem of your choice.

    [root@unixfoo23 ~]# mkfs.ext3  /root/myfs1
    mke2fs 1.35 (28-Feb-2004)
    /root/myfs1 is not a block special device.
    Proceed anyway? (y,n) y
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    131072 inodes, 262144 blocks
    13107 blocks (5.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=268435456
    8 block groups
    32768 blocks per group, 32768 fragments per group
    16384 inodes per group
    Superblock backups stored on blocks:
            32768, 98304, 163840, 229376

    Writing inode tables: done
    Creating journal (8192 blocks): done
    Writing superblocks and filesystem accounting information: done

    This filesystem will be automatically checked every 28 mounts or
    180 days, whichever comes first.  Use tune2fs -c or -i to override.

    [root@unixfoo23 ~]# file /root/myfs1
    /root/myfs1: Linux rev 1.0 ext3 filesystem data (large files)
    [root@unixfoo23 ~]#

  3. Mount the filesystem as a loopback device.

    [root@unixfoo23 ~]# mount -o loop /root/myfs1 /mnt

    [root@unixfoo23 ~]# df /mnt
    Filesystem           1K-blocks      Used Available Use% Mounted on
    /root/myfs1            1032088     34092    945568   4% /mnt
    [root@unixfoo23 ~]#

  4. If you need this permanantly , you can add this to /etc/fstab.
You can even create this virtual filesytem on a nfs mounted directory and again loopback-mount it on the machine.
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