Understanding VM Swap on Linux

VM swappiness is a setting in the Linux kernel that tells your system how aggressively it should use "swap space" compared to your computer's main memory (RAM). Think of swap space as a backup area on your hard drive that the system uses when RAM fills up.

• A high swappiness value means your system will try to move data from RAM to swap space more often.

• A low swappiness value means your system will try to keep data in RAM for longer, using swap space only when absolutely necessary.

In simple terms, the higher the swappiness value, the more your system will use the hard drive for memory overflow.

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DEFAULT SWAPPINESS VALUE

On many Linux distributions like RHEL and CentOS, the default swappiness value is often 60.

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HOW TO CHECK YOUR CURRENT SWAPPINESS

You can easily check the current swappiness value on your Linux system using one of these commands:

1. Using sysctl: sysctl vm.swappiness

   Example Output: vm.swappiness = 60

2. Reading the file directly: cat /proc/sys/vm/swappiness

   Example Output: 60

Both commands will show you the current swappiness setting.

‘df‘ command stand for linux “disk filesystem“

Linux has a strong built in utility called ‘df‘. The ‘df‘ command stand for “disk filesystem“, it is used to get full summary of available and used disk space usage of file system on Linux system.

Using ‘-h‘ parameter with (df -h) will shows the file system disk space statistics in “human readable” format, means it gives the details in bytes, mega bytes and gigabyte.
How to Check Disk Space in Linux

Useful df Command Examples

This article explain a way to get the full information of Linux disk space usage with the help of ‘df‘ command with their practical examples. So, you could better understand the usage of df command in Linux.
1. Check File System Disk Space Usage

The “df” command displays the information of device name, total blocks, total disk space, used disk space, available disk space and mount points on a file system.

[root@tecmint ~]# df

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/cciss/c0d0p2 78361192 23185840 51130588 32% /
/dev/cciss/c0d0p5 24797380 22273432 1243972 95% /home
/dev/cciss/c0d0p3 29753588 25503792 2713984 91% /data
/dev/cciss/c0d0p1 295561 21531 258770 8% /boot
tmpfs 257476 0 257476 0% /dev/shm

2. Display Information of all File System Disk Space Usage

The same as above, but it also displays information of dummy file systems along with all the file system disk usage and their memory utilization.

[root@tecmint ~]# df -a

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/cciss/c0d0p2 78361192 23186116 51130312 32% /
proc 0 0 0 - /proc
sysfs 0 0 0 - /sys
devpts 0 0 0 - /dev/pts
/dev/cciss/c0d0p5 24797380 22273432 1243972 95% /home
/dev/cciss/c0d0p3 29753588 25503792 2713984 91% /data
/dev/cciss/c0d0p1 295561 21531 258770 8% /boot
tmpfs 257476 0 257476 0% /dev/shm
none 0 0 0 - /proc/sys/fs/binfmt_misc
sunrpc 0 0 0 - /var/lib/nfs/rpc_pipefs

3. Show Disk Space Usage in Human Readable Format

Have you noticed that above commands displays information in bytes, which is not readable yet all, because we are in a habit of reading the sizes in megabytes, gigabytes etc. as it makes very easy to understand and remember.

The df command provides an option to display sizes in Human Readable formats by using ‘-h’ (prints the results in human readable format (e.g., 1K 2M 3G)).

[root@tecmint ~]# df -h

Filesystem Size Used Avail Use% Mounted on
/dev/cciss/c0d0p2 75G 23G 49G 32% /
/dev/cciss/c0d0p5 24G 22G 1.2G 95% /home
/dev/cciss/c0d0p3 29G 25G 2.6G 91% /data
/dev/cciss/c0d0p1 289M 22M 253M 8% /boot
tmpfs 252M 0 252M 0% /dev/shm

4. Display Information of /home File System

To see the information of only device /home file system in human readable format use the following command.

[root@tecmint ~]# df -hT /home

Filesystem Type Size Used Avail Use% Mounted on
/dev/cciss/c0d0p5 ext3 24G 22G 1.2G 95% /home

5. Display Information of File System in Bytes

To display all file system information and usage in 1024-byte blocks, use the option ‘-k‘ (e.g. –block-size=1K) as follows.

[root@tecmint ~]# df -k

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/cciss/c0d0p2 78361192 23187212 51129216 32% /
/dev/cciss/c0d0p5 24797380 22273432 1243972 95% /home
/dev/cciss/c0d0p3 29753588 25503792 2713984 91% /data
/dev/cciss/c0d0p1 295561 21531 258770 8% /boot
tmpfs 257476 0 257476 0% /dev/shm

6. Display Information of File System in MB

To display information of all file system usage in MB (Mega Byte) use the option as ‘-m‘.

[root@tecmint ~]# df -m

Filesystem 1M-blocks Used Available Use% Mounted on
/dev/cciss/c0d0p2 76525 22644 49931 32% /
/dev/cciss/c0d0p5 24217 21752 1215 95% /home
/dev/cciss/c0d0p3 29057 24907 2651 91% /data
/dev/cciss/c0d0p1 289 22 253 8% /boot
tmpfs 252 0 252 0% /dev/shm

7. Display Information of File System in GB

To display information of all file system statistics in GB (Gigabyte) use the option as ‘df -h‘.

[root@tecmint ~]# df -h

Filesystem Size Used Avail Use% Mounted on
/dev/cciss/c0d0p2 75G 23G 49G 32% /
/dev/cciss/c0d0p5 24G 22G 1.2G 95% /home
/dev/cciss/c0d0p3 29G 25G 2.6G 91% /data
/dev/cciss/c0d0p1 289M 22M 253M 8% /boot
tmpfs 252M 0 252M 0% /dev/shm

8. Display File System Inodes

Using ‘-i‘ switch will display the information of number of used inodes and their percentage for the file system.

[root@tecmint ~]# df -i

Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/cciss/c0d0p2 20230848 133143 20097705 1% /
/dev/cciss/c0d0p5 6403712 798613 5605099 13% /home
/dev/cciss/c0d0p3 7685440 1388241 6297199 19% /data
/dev/cciss/c0d0p1 76304 40 76264 1% /boot
tmpfs 64369 1 64368 1% /dev/shm

9. Display File System Type

If you notice all the above commands output, you will see there is no file system type mentioned in the results. To check the file system type of your system use the option ‘T‘. It will display file system type along with other information.

[root@tecmint ~]# df -T

Filesystem Type 1K-blocks Used Available Use% Mounted on
/dev/cciss/c0d0p2 ext3 78361192 23188812 51127616 32% /
/dev/cciss/c0d0p5 ext3 24797380 22273432 1243972 95% /home
/dev/cciss/c0d0p3 ext3 29753588 25503792 2713984 91% /data
/dev/cciss/c0d0p1 ext3 295561 21531 258770 8% /boot
tmpfs tmpfs 257476 0 257476 0% /dev/shm

10. Include Certain File System Type

If you want to display certain file system type use the ‘-t‘ option. For example, the following command will only display ext3 file system.

[root@tecmint ~]# df -t ext3

Filesystem 1K-blocks Used Available Use% Mounted on
/dev/cciss/c0d0p2 78361192 23190072 51126356 32% /
/dev/cciss/c0d0p5 24797380 22273432 1243972 95% /home
/dev/cciss/c0d0p3 29753588 25503792 2713984 91% /data
/dev/cciss/c0d0p1 295561 21531 258770 8% /boot

11. Exclude Certain File System Type

If you want to display file system type that doesn’t belongs to ext3 type use the option as ‘-x‘. For example, the following command will only display other file systems types other than ext3.

[root@tecmint ~]# df -x ext3

Filesystem 1K-blocks Used Available Use% Mounted on
tmpfs 257476 0 257476 0% /dev/shm

=====================
[root@tecmint ~]# df
[root@tecmint ~]# df -h
[root@tecmint ~]# df -a
[root@tecmint ~]# df -hT /home
[root@tecmint ~]# df -k
[root@tecmint ~]# df -m
[root@tecmint ~]# df -h
[root@tecmint ~]# df -i
[root@tecmint ~]# df -T
[root@tecmint ~]# df -t ext3
[root@tecmint ~]# df -x ext3

[root@tecmint ~]# df -aihT
=====================

(Disk Usage) “du” is a standard Unix/Linux command

The Linux “du” (Disk Usage) is a standard Unix/Linux command, used to check the information of disk usage of files and directories on a machine. The du command has many parameter options that can be used to get the results in many formats. The du command also displays the files and directory sizes in a recursively manner.
Check Disk Usage In Linux

Check Disk Usage of Files and Folders In Linux

1. To find out the disk usage summary of a /home/server directory tree and each of its sub directories. Enter the command as:

[root@]# du /home/server

40 /home/server/downloads
4 /home/server/.mozilla/plugins
4 /home/server/.mozilla/extensions
12 /home/server/.mozilla
12 /home/server/.ssh
689112 /home/server/Ubuntu-12.10
689360 /home/server

The output of the above command displays the number of disk blocks in the /home/server directory along with its sub-directories.

2. Using “-h” option with “du” command provides results in “Human Readable Format“. Means you can see sizes in Bytes, Kilobytes, Megabytes, Gigabytes etc.

[root@server]# du -h /home/server

40K /home/server/downloads
4.0K /home/server/.mozilla/plugins
4.0K /home/server/.mozilla/extensions
12K /home/server/.mozilla
12K /home/server/.ssh
673M /home/server/Ubuntu-12.10
674M /home/server

3. To get the summary of a grand total disk usage size of an directory use the option “-s” as follows.

[root@server]# du -sh /home/server

674M /home/server

4. Using “-a” flag with “du” command displays the disk usage of all the files and directories.

[root@server]# du -a /home/server

4 /home/server/.bash_logout
12 /home/server/downloads/uploadprogress-1.0.3.1.tgz
24 /home/server/downloads/Phpfiles-org.tar.bz2
40 /home/server/downloads
12 /home/server/uploadprogress-1.0.3.1.tgz
4 /home/server/.mozilla/plugins
4 /home/server/.mozilla/extensions
12 /home/server/.mozilla
4 /home/server/.bashrc
689108 /home/server/Ubuntu-12.10/ubuntu-12.10-server-i386.iso
689112 /home/server/Ubuntu-12.10
689360 /home/server

5. Using “-a” flag along with “-h” displays disk usage of all files and folders in human readeable format. The below output is more easy to understand as it shows the files in Kilobytes, Megabytes etc.

[root@server]# du -ah /home/server

4.0K /home/server/.bash_logout
12K /home/server/downloads/uploadprogress-1.0.3.1.tgz
24K /home/server/downloads/Phpfiles-org.tar.bz2
40K /home/server/downloads
12K /home/server/uploadprogress-1.0.3.1.tgz
4.0K /home/server/.mozilla/plugins
4.0K /home/server/.mozilla/extensions
12K /home/server/.mozilla
4.0K /home/server/.bashrc
673M /home/server/Ubuntu-12.10/ubuntu-12.10-server-i386.iso
673M /home/server/Ubuntu-12.10
674M /home/server

6. Find out the disk usage of a directory tree with its subtress in Kilobyte blcoks. Use the “-k” (displays size in 1024 bytes units).

[root@server]# du -k /home/server
40 /home/server/downloads
4 /home/server/.mozilla/plugins
4 /home/server/.mozilla/extensions
12 /home/server/.mozilla
12 /home/server/.ssh
689112 /home/server/Ubuntu-12.10
689360 /home/server

7. To get the summary of disk usage of directory tree along with its subtrees in Megabytes (MB) only. Use the option “-mh” as follows. The “-m” flag counts the blocks in MB units and “-h” stands for human readable format.

[root@server]# du -mh /home/server

40K /home/server/downloads
4.0K /home/server/.mozilla/plugins
4.0K /home/server/.mozilla/extensions
12K /home/server/.mozilla
12K /home/server/.ssh
673M /home/server/Ubuntu-12.10
674M /home/server

8. The “-c” flag provides a grand total usage disk space at the last line. If your directory taken 674MB space, then the last last two line of the output would be.

[root@server]# du -ch /home/server

40K /home/server/downloads
4.0K /home/server/.mozilla/plugins
4.0K /home/server/.mozilla/extensions
12K /home/server/.mozilla
12K /home/server/.ssh
673M /home/server/Ubuntu-12.10
674M /home/server
674M total

9. The below command calculates and displays the disk usage of all files and directories, but excludes the files that matches given pattern. The below command excludes the “.txt” files while calculating the total size of diretory. So, this way you can exclude any file formats by using flag “-–exclude“. See the output there is no txt files entry.

[root@server]# du -ah --exclude="*.txt" /home/server

4.0K /home/server/.bash_logout
12K /home/server/downloads/uploadprogress-1.0.3.1.tgz
24K /home/server/downloads/Phpfiles-org.tar.bz2
40K /home/server/downloads
12K /home/server/uploadprogress-1.0.3.1.tgz
4.0K /home/server/.bash_history
4.0K /home/server/.bash_profile
4.0K /home/server/.mozilla/plugins
4.0K /home/server/.mozilla/extensions
12K /home/server/.mozilla
4.0K /home/server/.bashrc
24K /home/server/Phpfiles-org.tar.bz2
4.0K /home/server/geoipupdate.sh
4.0K /home/server/.zshrc
120K /home/server/goaccess-0.4.2.tar.gz.1
673M /home/server/Ubuntu-12.10/ubuntu-12.10-server-i386.iso
673M /home/server/Ubuntu-12.10
674M /home/server

10. Display the disk usage based on modification of time, use the flag “–time” as shown below.

[root@server]# du -ha --time /home/server

4.0K 2012-10-12 22:32 /home/server/.bash_logout
12K 2013-01-19 18:48 /home/server/downloads/uploadprogress-1.0.3.1.tgz
24K 2013-01-19 18:48 /home/server/downloads/Phpfiles-org.tar.bz2
40K 2013-01-19 18:48 /home/server/downloads
12K 2013-01-19 18:32 /home/server/uploadprogress-1.0.3.1.tgz
4.0K 2012-10-13 00:11 /home/server/.bash_history
4.0K 2012-10-12 22:32 /home/server/.bash_profile
0 2013-01-19 18:32 /home/server/xyz.txt
0 2013-01-19 18:32 /home/server/abc.txt
4.0K 2012-10-12 22:32 /home/server/.mozilla/plugins
4.0K 2012-10-12 22:32 /home/server/.mozilla/extensions
12K 2012-10-12 22:32 /home/server/.mozilla
4.0K 2012-10-12 22:32 /home/server/.bashrc
24K 2013-01-19 18:32 /home/server/Phpfiles-org.tar.bz2
4.0K 2013-01-19 18:32 /home/server/geoipupdate.sh
4.0K 2012-10-12 22:32 /home/server/.zshrc
120K 2013-01-19 18:32 /home/server/goaccess-0.4.2.tar.gz.1
673M 2013-01-19 18:51 /home/server/Ubuntu-12.10/ubuntu-12.10-server-i386.iso
673M 2013-01-19 18:51 /home/server/Ubuntu-12.10
674M 2013-01-19 18:52 /home/server

=================
[root@server]# du /home/server
[root@server]# du -h /home/server
[root@server]# du -sh /home/server
[root@server]# du -a /home/server
[root@server]# du -ah /home/server
[root@server]# du -k /home/server
[root@server]# du -mh /home/server
[root@server]# du -ch /home/server
[root@server]# du -ah --exclude="*.txt" /home/server
[root@server]# du -ha --time /home/server
[root@server]# du -sach *
=================