Df command on Centos/VirtualBox

centosdisk-usagestoragevirtualbox

I'm studing the use of df, when i tried it on centos 7 on my virtualBox, i got this :

df -h 
Filesystem               Size  Used Avail Use% Mounted on
devtmpfs                 1.9G     0  1.9G   0% /dev
tmpfs                    1.9G     0  1.9G   0% /dev/shm
tmpfs                    1.9G  9.6M  1.9G   1% /run
tmpfs                    1.9G     0  1.9G   0% /sys/fs/cgroup
/dev/mapper/centos-root  8.0G  5.3G  2.8G  66% /
/dev/sda1               1014M  239M  776M  24% /boot
tmpfs                    379M   24K  379M   1% /run/user/1000

i don't understand from where all this space came from, because i have only 10G when i first created this VM, and 4G for the RAM, and in the configuration of the VM i get this :

Information when i click in storage  : 
type : Normal (VDI)
virtual size : 10G
reel size : 4.86
details : storage of differentiation
Emplacement : ...
attached to : centos (install snapshot)

Best Answer

df shows all mounted filesystems, which include tmpfs virtual filesystems that reside in memory.

From your df output you have just two filesystems saved on disk:

1 GB /boot on sda1 partition
8 GB / on centos-root logical volume

The remaining 1 GB from your disk is most likely used for swap which is not shown in df output (you can use lsblk to list block devices on your system, it will show swap too).

The content of remaining mountpoints you see (/dev, /run...) is stored in memory. These are special folders created dynamically by the OS (for example /dev contains special files that represent block and character devices in your system). RAM for these is allocated dynamically when needed, these don't actually take 2 GB of RAM each, the size is just an upper limit.

Related Solutions

Centos – How to resize / shifting partitions

Since you've partitioned your RAID as if it was a single disk, you can ignore the RAID altogether in this case. So it's merely a problem of resizing / shifting partitions.

So for example, you could shrink the www partition, delete the swap and then shift the root partition to the left in order to grow it.

Or, if that seems to complicated and you don't strictly need separate partitions, you could merge the root partition into your www partition since that's already large enough to hold both root and www. That's kind of what I would do.

# mount stuff
mkdir /mnt/root /mnt/www
mount /dev/md0p5 /mnt/root
mount /dev/md0p2 /mnt/www

# since /mnt/www will be the new root, move www files to /var/www
mkdir -p /mnt/www/var/www
mv /mnt/www/* /mnt/var/www/

# copy the root files
rsync -avAHSX /mnt/root/. /mnt/www/.

# comment out old root partition in fstab
# change /var/www to / in fstab

# update bootloader and reboot

This approach also has the advantage that if anything goes wrong, the original root partition is still intact, so you can revert the operation.

Once everything is working fine with the merged root+www partition, you can delete the old root partition and grow it to the full disk size.

Or you could decide that you want to stick with separate partitions after all and move the www files to the old root partition, if you think that's going to be large enough for your www in the foreseeable future.

Or you could shrink the www partition to make room for a new one.

Endless possibilities...

Best Answer

Related Solutions

Centos – How to resize / shifting partitions

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