Drop all ping packets

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To drop all ping packets all together
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You can setup kernel variable to drop all ping packets.

# echo "1" > /proc/sys/net/ipv4/icmp_echo_ignore_all

This instructs the kernel to simply ignore all ping requests (ICMP type 0 messages).


To enable ping request type the command:

# echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_all

[or]

You can drop by adding following line to /etc/sysctl.conf file:

net.ipv4.icmp_echo_ignore_all = 1

Save and close the file.

To Find The Details Of The CPU

To Find The Details Of The CPU , Instead Of Opening The File cat /etc/cpuinfo

# dmidecode -t type

Type Information
----------------------------------------
0 BIOS
1 System
2 Base Board
3 Chassis
4 Processor
5 Memory Controller
6 Memory Module
7 Cache
8 Port Connector
9 System Slots
10 On Board Devices
11 OEM Strings
12 System Configuration Options
13 BIOS Language
14 Group Associations
15 System Event Log
16 Physical Memory Array
17 Memory Device
18 32-bit Memory Error
19 Memory Array Mapped Address
20 Memory Device Mapped Address
21 Built-in Pointing Device
22 Portable Battery
23 System Reset
24 Hardware Security
25 System Power Controls
26 Voltage Probe
27 Cooling Device
28 Temperature Probe
29 Electrical Current Probe
30 Out-of-band Remote Access
31 Boot Integrity Services
32 System Boot
33 64-bit Memory Error
34 Management Device
35 Management Device Component
36 Management Device Threshold Data
37 Memory Channel
38 IPMI Device
39 Power Supply

Linux Ext2,Ext3,Ext4 File systems

A LINUX file system is a collection of files and directories stored. Each file system is stored in a separate whole disk partition.here we see file system types

The ext2 (second extended file system) is a file system for the Linux kernel. It was initially designed by Remy Card as a replacement for the extended file system (ext).It was introduced with the 1.0 kernel in 1993.Ext2 is flexible,can handle file system up to 4 TB,and supports long file names up to 1012 characters,it has sparse super blocks feature which increase file system performance.In case any user processes fill up a file system,ext2 normally reserves about 5% of disk blocks for exclusive use by root so that root can easily recover from that situation.

The ext3 (third extended file system) is a journal ed file system that is commonly used by the Linux kernel. It is the default file system for many popular Linux distributions,Stephen Tweedie developed ext3.It provides all the features of ext2,and also features journaling and backward compatibility with ext2.The backward compatibility enables you to still run kernels that are only ext2-aware with ext3 partitions.we can also use all of the ext2 file system tuning,repair and recovery tools with ext3 also you can upgrade an ext2 file system to an ext3 file system without losing any of your data.
Ext3’s journaling feature speeds up the amount of time ,in ext2 when a file system is uncleanly mounted ,the whole file system must be checked.This takes a long time on large file systems.On an ext3 system ,the system keeps a record of uncommitted file transactions and applies only those transactions when the system is brought back up.So a complete system check is not required and the system will come back up much faster.

The ext4 (fourth extended file system) is a journaling file system for Linux,Ext4 is part of the Linux 2.6.28 kernel,Ext4 is the evolution of the most used Linux file system, Ext3. In many ways, Ext4 is a deeper improvement over Ext3 than Ext3 was over Ext2. Ext3 was mostly about adding journaling to Ext2, but Ext4 modifies important data structures of the file system such as the ones destined to store the file data. The result is a filesystem with an improved design, better performance, reliability and features.developed by Mingming Cao,Andreas Dilger,Alex Zhuravlev,Dave Kleikamp,Theodore Ts'o, Eric Sandeen,Sam Naghshineh and others.

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

Strange Linux Commands Stands For

awk = "Aho Weinberger and Kernighan"
            This language was named by its authors, Al Aho, Peter Weinberger and Brian Kernighan.

cat = "CATenate"
The cat command is a standard Unix program used to concatenate and display files. The name is from catenate, a synonym of concatenate.

grep = "Global Regular Expression Print"
    grep comes from the ed command to print all lines matching a certain pattern g/re/p where re is a regular expression.

    fgrep = "Fixed GREP"
    fgrep searches for fixed strings only. The "f" does not stand for "fast" - in fact, "fgrep foobar *.c" is usually slower than "egrep foobar *.c"
   
    egrep = "Extended GREP"
   
nroff = "New ROFF"
troff = "Typesetter new ROFF"
    These are descendants of "roff", which was a re-implementation of the Multics "runoff" program (a program that you'd use to "run off" a good copy of a document)

tee = T
    From plumbing terminology for a T-shaped pipe splitter.

Perl = "Practical Extraction and Report Language"
Perl = "Pathologically Eclectic Rubbish Lister"
    The Perl language is Larry Wall's highly popular freely-available completely portable text, process, and file manipulation tool that bridges the gap between shell and C programming.