In this post, we will be discuss the command “du” or disk usage. The du command is a handy command to check folder/file sizes in Linux. This command comes with a lots of options which when combining them together can give you a very powerful way to check file/folder size usage of your disk.

Syntax for Linux du command

du [OPTION]... [FILE]...

Basic du command usage examples

Example 1: Execute du command with no options. As you can see in this example, using du without any option will list folders recursively by default the size of each file under the directory you chose. The file size here is shown in KB by default. It will show the hidden files and the size of the parent directory as an entry, and the child directories as separate entries. However it will go up to the last directory

[root@linuxnix /]# du /opt
4 /opt/rh
8 /opt

Example 2: If you don’t want to see output in KB’s, use the -h option for a human readable output. Adding the -h option will give you the output in a more readable file size format, with base 1024, it will show the 1024 KB file as 1M which is more easier to read.

[root@linuxnix mnt]# du -h /mnt
100K /mnt/dir1
104K /mnt

Example 3: If you are wishing to get the disk space utilization of the whole directory, without going into details of any sub directories. Use the -s option for a summarized output and eventually files, you can use the -s option.

 [root@linuxnix ~]# du -sh /var
 1.1G /var

Or even one level down than just /var to include sub-directories

 [root@linuxnix ~]# du -sh /var/*
 4.0K /var/account
 151M /var/cache
 4.0K /var/crash
 4.0K /var/cvs
 4.0K /var/nis
 4.0K /var/opt
 4.0K /var/preserve
 384K /var/run
 73M /var/spool
 160K /var/tmp
 699M /var/www
 12K /var/yp

Example 4: Using the -a option “with caution”. If you want to go as much granular as possible, up to the last file in the chain, including any hidden files, use the -a option. Please note that you can not use -s and -a in the same command.

[root@linuxnix mnt]# du -ah /mnt
 0 /mnt/dir1/.file5
 96K /mnt/dir1/file1
 0 /mnt/dir1/file3
 0 /mnt/dir1/.file6
 0 /mnt/dir1/file2
 100K /mnt/dir1
 104K /mnt

Example 5: We can even control how many levels we can go down the sub directories using the[ –max-depth=N] option. It basically will view everything as long as it is N or less levels under the directory you specified.

 [root@linuxnix mnt]# du -ah --max-depth=1 /var/
 4.0K /var/local
 12K /var/yp
 4.0K /var/crash
 160K /var/tmp
 4.0K /var/opt
 384K /var/run
 24K /var/lock
 0 /var/mail
 4.0K /var/account
 145M /var/lib
 699M /var/www

Example 6: Now let us do the same as the previous example, but add the –time option
this will increase your visibility, it will show you a new column with the time last modified shown.

[root@linuxnix mnt]# du -ah --max-depth=1 --time /var/
 4.0K 2011-09-23 13:50 /var/local
 12K 2015-08-07 18:38 /var/yp
 4.0K 2016-01-06 13:36 /var/crash
 160K 2016-02-08 11:49 /var/tmp
 4.0K 2011-09-23 13:50 /var/opt
 384K 2016-03-03 17:46 /var/run
 24K 2016-03-03 03:50 /var/lock
 0 2015-08-07 18:35 /var/mail
 4.0K 2015-08-07 18:46 /var/account
 145M 2016-03-03 19:09 /var/lib
 699M 2016-02-28 09:10 /var/www
 4.0K 2011-09-23 13:50 /var/nis
 49M 2016-03-03 19:14 /var/log
 1.1G 2016-03-03 19:14 /var/

Example 7: What if you are not interested in some file patterns, and you wish to exclude them, use the [–exclude=pattern] option
Let’s examine the below directory /root/imagefiles/

 [root@linuxnix imagefiles]# du -ah /root/imagefiles/
 20K /root/imagefiles/storage.state
 4.0K /root/imagefiles/partdisk.txt
 4.0K /root/imagefiles/osdisk.txt
 84K /root/imagefiles/storage.log
 4.0K /root/imagefiles/hdparm.out
 120K /root/imagefiles/ks-script-dMBeha
 4.0K /root/imagefiles/chompstr
 4.0K /root/imagefiles/.treeinfo
 4.0K /root/imagefiles/nwoptsw.txt
 0 /root/imagefiles/nwparameters
 4.0K /root/imagefiles/pre.log
 56K /root/imagefiles/yum.log
 144K /root/imagefiles/ks.cfg

Now, say we want to view this directory, but we are not interested in the .log file type, let’s do it one more time with the –exclude option

 [root@linuxnix imagefiles]# du -ah --exclude=*log /root/imagefiles/
 20K /root/imagefiles/storage.state
 4.0K /root/imagefiles/partdisk.txt
 4.0K /root/imagefiles/osdisk.txt
 4.0K /root/imagefiles/hdparm.out
 120K /root/imagefiles/ks-script-dMBeha
 4.0K /root/imagefiles/chompstr
 4.0K /root/imagefiles/nwdisk.txt
 4.0K /root/imagefiles/nwsystem
 4.0K /root/imagefiles/nwpart.txt
 28K /root/imagefiles/ks-script-EZvwhh

Example 8: We can even exclude files coming from different file systems. Examine the below File system, I am using /home as a file system and /home/rsasoc as a different file system. Suppose I want to check disk utilization of /home only, and ignore /home/rsasoc file system then use -x option.

[root@linuxnix ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-root 7.8G 6.7G 682M 91% /
tmpfs 48G 0 48G 0% /dev/shm
/dev/sda1 248M 59M 176M 26% /boot
/dev/mapper/VolGroup00-usrhome 3.9G 8.1M 3.7G 1% /home
/dev/mapper/VolGroup01-rsasoc 200G 69G 132G 35% /home/rsasoc 
/dev/mapper/VolGroup00-tmp 20G 526M 19G 3% /tmp
/dev/mapper/VolGroup00-var 7.8G 434M 7.0G 6% /var 
/dev/mapper/VolGroup01-uax 200G 722M 200G 1% /var/lib/netwitness
/dev/mapper/VolGroup00-rabmq 20G 36M 20G 1% /var/lib/rabbitmq
/dev/mapper/VolGroup00-varlog 9.8G 1.1G 8.2G 12% /var/log
/dev/mapper/VolGroup00-nwhome 30G 4.2G 26G 15% /var/netwitness
/dev/mapper/VolGroup01-broker 200G 68G 133G 34% /var/netwitness/broker
/dev/mapper/VolGroup01-redb 200G 71M 200G 1% /var/netwitness/database
/dev/mapper/VolGroup00-ipdbext 30G 33M 30G 1% /var/netwitness/ipdbextractor
/dev/mapper/VolGroup00-vartmp 3.9G 8.0M 3.7G 1% /var/tmp
[root@linuxnix ~]# du -hx /home
 16K /home/lost+found
 16K /home/cindy
 0 /home/rsasoc
 36K /home

Observer that /home/rsasoc is showing as zero, when it is actually 69 GB utilized.

Example 9: Combining du with sort, to sort the output based on maximum utilization.
Let’s now try to sort the output of du, so we check the maximum utilization files first.

du -sh /* 2> /dev/null | sort -rh

Where 2> /dev/null will direct any errors to /dev/null , sort -r will sort reversely “bigger size first”.

[root@linuxnix ~]# du -sh /* 2> /dev/null | sort -rh
74G /var
69G /home
4.4G /usr
1.1G /opt
666M /root
389M /tmp
258M /lib
57M /boot
 37M /etc
 27M /lib64
 22M /share01
 13M /sbin
 6.2M /bin
 2.7M /doc
 252K /dev
 16K /lost+found
 4.0K /srv
 4.0K /postinstall.log
 4.0K /mnt
 4.0K /media
 0 /sys
 0 /selinux
 0 /proc
 0 /mongodb-27017.sock

Example 10: I have hidden directories in my folder, how can I list only hidden folders size

du -hs .[!.]*

Let me explain what .[!.]* is all about. In order to understand this you should know . indicates present directory and .. indicates parent directory. what .[!.] indicates is my folder starts with . and it will not contain . again after the first dot. Which means we are effectively eliminating .. which is my parent directory. and .[!.]* is all the hidden files/folder in that given directory.

Example 11: Above example lists only hidden files and directories, how about list all folders/files in that directory.

du -hs .[!.]* *

Example output:

8.0K    .thumbnails
1.4M    .thunderbird
8.0K    .vim
28K    .viminfo
522M    .wine
4.0K    .Xauthority
4.0K    .xsession-errors
4.0K    .xsession-errors.old
2.0G    10.04_clean_image_for_12.04_16072015
4.0K    20150430-assets_rcvr.csv
4.0K    2.4.0-A2 load tests

Example 12: Some times we want to execute this command in many folders which is tedious job, how about making this as an alias so that the typing takes less time.

alias sm="du -hs * | grep -E ^[0-9]+M"

alias sg="du -hs * | grep -E ^[0-9]+G"

The first command will list all the folders which are more than or equal to 1M and less than 1000M and second command will show all the files/folder which are more than or equal to 1G


surendra@linuxnix:~$ sm

860M    code
27M    Music
26M    Pictures
579M    ubuntu-14.04.2-server-i386.iso surendra@linuxnix:~$ sg
16G    Desktop

Example 13: If you want to round the way it counts to the nearest block size, so it acts in a way like df “we will get to this next”, you can use the –block-size option

 [root@linuxnix cindy]# du -x --block-size=1K /home
 16 /home/lost+found
 20 /home/cindy
 0 /home/rsasoc
 40 /home

If you haven’t checked “df” command yet, please give it a look at our df command examples whereas du and df might seem similar in the way they show you your disk utilization, in fact there are a lots of differences.
Mostly, “du” will always count on files, and this will be the building block used to provide the total disk space utilized.In a sense of how many files that actually exist, and how they sum up to build this utilization. whereas “df” will always count on file system as the measure, and by that it will check the utilization it calculates for each file system mounted on a certain directory.

 [root@linuxnix ~]# df -h /var
 Filesystem Size Used Avail Use% Mounted on
/dev/sda1 452G 89G 359G 20% /
[root@linuxnix ~]# df -h /
 Filesystem Size Used Avail Use% Mounted on
 /dev/sda1 452G 89G 359G 20% /

Another huge misleading difference is du calculates the sum of separate file sizes, df is designed to count blocks used by file system. in a way that if block size is 1 KB “the default value”, if for instance a file is like 800 bytes utilizing one block. df will count the blocks and multiplies by 1024 to count, whereas again du will sum the actual size of each file, and outcomes a much more accurate number. Finally, in a world where all Linux file systems are Journaling, these journals are simply used disk space to keep track of files that are loaded in memory. this disk space used is not of your actual files but rather for the journal of your loaded files in memory. again df will calculate these [though they are not actually your files], whereas du will not. So basically in a nut shell and to sum up, if you are willing to get a big picture of how heavily your disk is utilized and ready to ignore willingly a margin or error, df command will be your tool, it is much faster than du and with much less processing. However if you are willing to be very granular, and in the scope of directories and the zoomed-in picture and willing to spend more time and CPU processing in return, then surely you will be using du and not df.

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Mr Surendra Anne is from Vijayawada, Andhra Pradesh, India. He is a Linux/Open source supporter who believes in Hard work, A down to earth person, Likes to share knowledge with others, Loves dogs, Likes photography. He works as Devops Engineer with Taggle systems, an IOT automatic water metering company, Sydney . You can contact him at surendra (@) linuxnix dot com.