How to check free space in Ubuntu?

The sizes of files and directories can be listed using:
ls -l

To see the free space left in partitions, use:
df -h

Other filters for df are given below:

`-h'
`--human-readable'
     Append a size letter such as `M' for megabytes to each size.
     Powers of 1024 are used, not 1000; `M' stands for 1,048,576 bytes.
     Use the `-H' or `--si' option if you prefer powers of 1000.

`-H'
`--si'
     Append a size letter such as `M' for megabytes to each size.  (SI
     is the International System of Units, which defines these letters
     as prefixes.)  Powers of 1000 are used, not 1024; `M' stands for
     1,000,000 bytes.  Use the `-h' or `--human-readable' option if you
     prefer powers of 1024.

`-i'
`--inodes'
     List inode usage information instead of block usage.  An inode
     (short for index node) is contains information about a file such
     as its owner, permissions, timestamps, and location on the disk.

`-k'
`--kilobytes'
     Print sizes in 1024-byte blocks, overriding the default block size.

`-l'
`--local'
     Limit the listing to local filesystems.  By default, remote
     filesystems are also listed.

`-m'
`--megabytes'
     Print sizes in megabyte (that is, 1,048,576-byte) blocks.

Source: [1] [2] 

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