To Clear Linux Memory Cache

To free pagecache:

# sync; echo 1 > /proc/sys/vm/drop_caches

To free dentries and inodes:

# sync; echo 2 > /proc/sys/vm/drop_caches

To free pagecache, dentries and inodes:

# sync; echo 3 > /proc/sys/vm/drop_caches

==> sync - flush file system buffers

File Fragmentation checking on Linux

To find file fragmentation information for a specific file,we can use filefrag command.
filefrag reports on how badly fragmented a particular file. It makes allowances for indirect blocks for ext2 and ext3 filesystems, but can be used on files for any filesystem.

syntax:

filefrag -v (filename)

# filefrag -v /home/example/example.txt

-v   => verbose when checking for file fragmentation

ouptput:(for example)

Checking example.txt
Filesystem type is: ef53
Filesystem cylinder groups is approximately 606
Blocksize of file example.txt is 4096
File size of example.txt is 1194 (1 blocks)
First block: 7006588
Last block: 7006588
example.txt: 1 extent found

Command to check UUID

In your /etc/fstab file, you have have seen an entry that looks UUID=c81355eb-96d2-458a-8ce0-3fa12a04cb8e instead of a more familiar disk drive designation, such as /dev/hda1. Such entries are called universally unique identifiers (UUID). You can use these 128-bit numbers to make hard disk management easier.

This following command is used to print the UUID for a device. This may be used with UUID= in /etc/fstab to name devices that works even if disks are added and removed. redhat uses this in /etc/fstab file.

Print UUID to a selected  partition /dev/sda1

#blkid -o value -s UUID /dev/sda1

Print all UUIDs

#blkid -o value -s UUID