Why are partition size and df output different

disk-usagepartition

I have a partition /dev/sda1.
Disk utility shows it has the capacity of 154 GB.
df -h shows

Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1             123G  104G   14G  89% /
devtmpfs             1006M  280K 1006M   1% /dev
none                 1007M  276K 1006M   1% /dev/shm
none                 1007M  216K 1006M   1% /var/run
none                 1007M     0 1007M   0% /var/lock
none                 1007M     0 1007M   0% /lib/init/rw

Why are the results different? Where are the missing 31 GB?

Best Answer

One reason the partition capacities can differ is that some space is reserved for root, in the event the partitions become full. If there is no space reserved for root, and the partitions become full, the system cannot function. However, this difference is usually of the order of 1%, so that does not explain the difference in your case. From the man page for df

If an argument is the absolute file name of a disk device node containing a mounted file system, df shows the space available on that file system rather than on the file system containing the device node (which is always the root file system).

So df is really showing the size of your filesystem, which is usually the size of the device, but this may not be true in your case. Does your filesystem extend over the whole of your partition?

Does

resize2fs /dev/sda1

make any difference? This command tries to increase your filesystem to cover the entire partition. But make sure you have a backup if you try this.

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