df and du

'du' - Finding the size of a directory

$ du
Typing the above at the prompt gives you a list of directories that exist in the current directory along with their sizes. The last line of the output gives you the total size of the current directory including its subdirectories. The size given includes the sizes of the files and the directories that exist in the current directory as well as all of its subdirectories. Note that by default the sizes given are in kilobytes. 


$ du / -h --max-depth 1 list the same info in GB/MB for the root directory and go only one level in depth/down

$ du /home/deyan
The above command would give you the directory size of the directory /home/deyan


$ du -h
This command gives you a better output than the default one. The option '-h' stands for human readable format. So the sizes of the files / directories are this time suffixed with a 'k' if its kilobytes and 'M' if its Megabytes and 'G' if its Gigabytes.

$ du -ah
This command would display in its output, not only the directories but also all the files that are present in the current directory. Note that 'du' always counts all files and directories while giving the final size in the last line. But the '-a' displays the filenames along with the directory names in the output. '-h' is once again human readable format.


$ du -c
This gives you a grand total as the last line of the output. So if your directory occupies 30MB the last 2 lines of the output would be

30M .
30M total

The first line would be the default last line of the 'du' output indicating the total size of the directory and another line displaying the same size, followed by the string 'total'. This is helpful in case you this command along with the grep command to only display the final total size of a directory as shown below.


$ du -ch | grep total
This would have only one line in its output that displays the total size of the current directory including all the subdirectories.


$ du -s
This displays a summary of the directory size. It is the simplest way to know the total size of the current directory.


$ du -S
This would display the size of the current directory excluding the size of the subdirectories that exist within that directory. So it basically shows you the total size of all the files that exist in the current directory.

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'df' - finding the disk free space / disk usage

$ df
Typing the above, outputs a table consisting of 6 columns. All the columns are very easy to understand. Remember that the 'Size', 'Used' and 'Avail' columns use kilobytes as the unit. The 'Use%' column shows the usage as a percentage which is also very useful.


$ df -h
Displays the same output as the previous command but the '-h' indicates human readable format. Hence instead of kilobytes as the unit the output would have 'M' for Megabytes and 'G' for Gigabytes.

Remove a symbolik link in Linux

Symbolik link is one that points to a file or directory, a kind of shortcut.
When it needs to be removed and you use the auto fill in of commands in the shell (TAB key) and you type rm then the name of the link, it will automatically add the name of the link and add a slash. This slash must be deleted in the command in order to be able to delete the symlink.

# correct way 
rm mySymLink
# incorrectly added slash
rm mySymLink/

The first one means you delete a file (which actually is the symlink) while the second is you want to delete a directory.

That's why you will get error you try to delete directory.

Also file permissions might be needed to be set up.