Physical memory full issue: Create Linux swap file after installing the linux operating system step by step guide

November 19, 2018 Add Comment Edit

Physical memory full issue: Create Linux swap file after installing the linux operating system step by step guide

In this article we learn how to create linux swap file after installing linux operating system , how to activate swap file after installing the swap file and how to remove swap file from linux operating system.

What is SWAP in linux

SWAP file is a space on disk which is taking over the control that means all inactive pages are moved from the physical memory of the system to the SWAP space when all physical memory is consumed or full.

How to create and activate SWAP file on disk of linux system

To create SWAP file on disk of a linux system we need to execute the below command.

We want to create SWAP file named (swapfile) with size 2GB on / partition.To do this we execute the below command.

[root@techrideradmin ~]# dd if=/dev/zero of=/swapfile bs=1M count=2048

2048+0 records in

2048+0 records out

2147483648 bytes (2.1 GB) copied, 25.9823 s, 82.7 MB/s

Create Linux swap file after installing the linux operating system step by step guide

After creating this we need to format it into SWAP. To do this we execute the below command.

[root@techrideradmin ~]# mkswap /swapfile

Setting up swapspace version 1, size = 2097148 KiB

no label, UUID=3653e4ed-30fb-4c7d-971f-4fd3bc22396e

Now we need to change the permission of the SWAP file .Only root user can read and write the file. To do this we need to execute the below command.

[root@techrideradmin ~]# chmod 600 /swapfile

To activate the SWAP file and verify the SWAP file we need to execute the below commands.

[root@techrideradmin ~]# swapon -a

[root@techrideradmin ~]# swapon -s

To make change permanently we append the following line into the “/etc/fstab”.

/swapfile swap swap defaults 0 0

After doing all the above steps we finally verify the SWAP file to execute the below command.

[root@techrideradmin ~]# free –g

How to remove SWAP file from the linux system.

To remove the SWAP file from the linux system first we need to deactivate the SWAP file using the below command.

[root@techrideradmin ~]# swapoff -a

After that we remove the SWAP file entry from the “/etc/fstab”.

And finally we remove the /swapfile using the below command.

[root@techrideradmin ~]# rm /swapfile

rm: remove regular file `/swapfile'? y

Setup software RAID1(data mirroring) using mdadm tool on two disks in linux with step by step guide

November 11, 2018 Add Comment Edit

Setup software RAID1(data mirroring) using mdadm tool on two disks in linux with step by step guide

In this article we learn how to create software RAID1 using mdadm tool on two hard disks in linux operating system.

What is RAID1

It is called data mirroring because it read write the identical data among the multiple disks. While one disk is failure we can retrieve data from the other working disk. So it provides redundancy .while we replace the new disk in the place of failure disk data will automatically sync with each other.

Setup software RAID1(data mirroring) using mdadm tool

Step1: Before creating software RAID1 we need to verify the partition table. To verify it we need to execute the below command.

#fdisk -l

Disk /dev/sda: 8589 MB, 8589934592 bytes

255 heads, 63 sectors/track, 1044 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x000ef612

Device Boot Start End Blocks Id System

/dev/sda1 * 1 64 512000 83 Linux

Partition 1 does not end on cylinder boundary.

/dev/sda2 64 1045 7875584 8e Linux LVM

Disk /dev/sdb: 2147 MB, 2147483648 bytes

255 heads, 63 sectors/track, 261 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000

Disk /dev/sdc: 2147 MB, 2147483648 bytes

255 heads, 63 sectors/track, 261 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000

In the above output we saw that we have two disks that is /dev/sdb and /dev/sdc. Using these two disks we create RAID1.

Step2: Now we need to verify that is there existing raid is configured or not using the below command.

[root@localhost ~]# mdadm --examine /dev/sd[b-c]

mdadm: No md superblock detected on /dev/sdb.

mdadm: No md superblock detected on /dev/sdc.

There is no existing raid is configured.

Step3: Now creating(sdb and sdc) partition for RAID using fdisk command.

Instruction to create partition

[root@localhost ~]# fdisk /dev/sdb

Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel

Building a new DOS disklabel with disk identifier 0xc77fae91.

Changes will remain in memory only, until you decide to write them.

After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

WARNING: DOS-compatible mode is deprecated. It's strongly recommended to

switch off the mode (command 'c') and change display units to

sectors (command 'u').

Command (m for help): n

Command action

e extended

p primary partition (1-4)

Partition number (1-4): 1

First cylinder (1-261, default 1):

Using default value 1

Last cylinder, +cylinders or +size{K,M,G} (1-261, default 261):

Using default value 261

Command (m for help): p

Disk /dev/sdb: 2147 MB, 2147483648 bytes

255 heads, 63 sectors/track, 261 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0xc77fae91

Device Boot Start End Blocks Id System

/dev/sdb1 1 261 2096451 83 Linux

After that we press “L” key to list all available types. And then press “t” to choose the partition and then choose “fd” for linux auto raid.after that press “w” to write changes.

Command (m for help): l

0 Empty 24 NEC DOS 81 Minix / old Lin bf Solaris

1 FAT12 39 Plan 9 82 Linux swap / So c1 DRDOS/sec (FAT-

2 XENIX root 3c PartitionMagic 83 Linux c4 DRDOS/sec (FAT-

3 XENIX usr 40 Venix 80286 84 OS/2 hidden C: c6 DRDOS/sec (FAT-

4 FAT16 <32M 41 PPC PReP Boot 85 Linux extended c7 Syrinx

5 Extended 42 SFS 86 NTFS volume set da Non-FS data

6 FAT16 4d QNX4.x 87 NTFS volume set db CP/M / CTOS / .

7 HPFS/NTFS 4e QNX4.x 2nd part 88 Linux plaintext de Dell Utility

8 AIX 4f QNX4.x 3rd part 8e Linux LVM df BootIt

9 AIX bootable 50 OnTrack DM 93 Amoeba e1 DOS access

a OS/2 Boot Manag 51 OnTrack DM6 Aux 94 Amoeba BBT e3 DOS R/O

b W95 FAT32 52 CP/M 9f BSD/OS e4 SpeedStor

c W95 FAT32 (LBA) 53 OnTrack DM6 Aux a0 IBM Thinkpad hi eb BeOS fs

e W95 FAT16 (LBA) 54 OnTrackDM6 a5 FreeBSD ee GPT

f W95 Ext'd (LBA) 55 EZ-Drive a6 OpenBSD ef EFI (FAT-12/16/

10 OPUS 56 Golden Bow a7 NeXTSTEP f0 Linux/PA-RISC b

11 Hidden FAT12 5c Priam Edisk a8 Darwin UFS f1 SpeedStor

12 Compaq diagnost 61 SpeedStor a9 NetBSD f4 SpeedStor

14 Hidden FAT16 <3 63 GNU HURD or Sys ab Darwin boot f2 DOS secondary

16 Hidden FAT16 64 Novell Netware af HFS / HFS+ fb VMware VMFS

17 Hidden HPFS/NTF 65 Novell Netware b7 BSDI fs fc VMware VMKCORE

18 AST SmartSleep 70 DiskSecure Mult b8 BSDI swap fd Linux raid auto

1b Hidden W95 FAT3 75 PC/IX bb Boot Wizard hid fe LANstep

1c Hidden W95 FAT3 80 Old Minix be Solaris boot ff BBT

1e Hidden W95 FAT1

Command (m for help): t

Selected partition 1

Hex code (type L to list codes): fd

Changed system type of partition 1 to fd (Linux raid autodetect)

Command (m for help): p

Disk /dev/sdb: 2147 MB, 2147483648 bytes

255 heads, 63 sectors/track, 261 cylinders

Units = cylinders of 16065 * 512 = 8225280 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0xc77fae91

Device Boot Start End Blocks Id System

/dev/sdb1 1 261 2096451 fd Linux raid autodetect

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.

Same above steps we have to follow to create partition on /dev/sdc.

Step4: Once partitions has been created we need to verify the changes using the below command.

[root@localhost ~]# mdadm --examine /dev/sd[b-c]

/dev/sdb:

MBR Magic : aa55

Partition[0] : 4192902 sectors at 63 (type fd)

/dev/sdc:

MBR Magic : aa55

Partition[0] : 4192902 sectors at 63 (type fd)

Step5: creating RAID md devices using the below command.

[root@localhost ~]# mdadm --create /dev/md0 --level=mirror --raid-devices=2 /dev/sd[b-c]1

mdadm: Note: this array has metadata at the start and

may not be suitable as a boot device. If you plan to

store '/boot' on this device please ensure that

your boot-loader understands md/v1.x metadata, or use

--metadata=0.90

Continue creating array? y

mdadm: Defaulting to version 1.2 metadata

mdadm: array /dev/md0 started.

Step6: verify raid creation using the following command.

[root@localhost ~]# cat /proc/mdstat

Personalities : [raid0] [raid1]

md0 : active raid1 sdc1[1] sdb1[0]

2095424 blocks super 1.2 [2/2] [UU]

[==============>......] resync = 74.7% (1565888/2095424) finish=0.5min speed=16704K/sec

unused devices: <none>

Setup software RAID1(data mirroring) using mdadm tool on two disks in linux with step by step guide

you can also execute the below command to know the md details.

[root@localhost ~]# mdadm --detail /dev/md0

/dev/md0:

Version : 1.2

Creation Time : Fri Dec 31 21:00:39 2010

Raid Level : raid1

Array Size : 2095424 (2046.31 MiB 2145.71 MB)

Used Dev Size : 2095424 (2046.31 MiB 2145.71 MB)

Raid Devices : 2

Total Devices : 2

Persistence : Superblock is persistent

Update Time : Fri Dec 31 21:02:23 2010

State : clean, resyncing

Active Devices : 2

Working Devices : 2

Failed Devices : 0

Spare Devices : 0

Resync Status : 83% complete

Name : localhost.localdomain:0 (local to host localhost.localdomain)

UUID : 94fe9ea1:18bef4c8:d5cd7760:4af176a7

Events : 13

Number Major Minor RaidDevice State

0 8 17 0 active sync /dev/sdb1

1 8 33 1 active sync /dev/sdc1

Step7: now create a directory , assign a file system and mount on the creating directory.

[root@localhost ~]# mkdir /raid1

[root@localhost ~]# mkfs.ext4 /dev/md0

mke2fs 1.43-WIP (20-Jun-2013)

Filesystem label=

OS type: Linux

Block size=4096 (log=2)

Fragment size=4096 (log=2)

Stride=0 blocks, Stripe width=0 blocks

131072 inodes, 523856 blocks

26192 blocks (5.00%) reserved for the super user

First data block=0

Maximum filesystem blocks=536870912

16 block groups

32768 blocks per group, 32768 fragments per group

8192 inodes per group

Superblock backups stored on blocks:

32768, 98304, 163840, 229376, 294912

Allocating group tables: done

Writing inode tables: done

Creating journal (8192 blocks): done

Writing superblocks and filesystem accounting information: done

[root@localhost ~]# mount /dev/md0 /raid1

Step8: now check using df –h command.

[root@localhost ~]# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/mapper/VolGroup-lv_root

6.5G 862M 5.3G 14% /

tmpfs 244M 0 244M 0% /dev/shm

/dev/sda1 477M 72M 376M 17% /boot

/dev/md0 2.0G 3.0M 1.9G 1% /raid1

Brief Introduction of RAID and advantage and drawback of different types of RAID levels

November 11, 2018 Add Comment Edit

Brief Introduction of RAID and advantage and drawback of different types of RAID levels

In this article we learn about the definition of RAID, different categories of RAID and explained the advantage and drawback of different levels of RAID.

Brief Introduction of RAID-What is RAID

Full form of RAID is redundant array of independent disks that store data among the multiple disks to provide huge performance and to provide fault tolerance to the system.

Brief Introduction of RAID and advantage and drawback of different types of RAID levels

Different categories of RAID

There are two categories of RAID one is hardware RAID and other is software RAID.

Hardware RAID: Hardware RAID is managed by the RAID controller.

Software RAID: Software RAID is the part of os and it is very cost effective as we don’t need any additional hardware to configure the software RAID.

Different levels of RAID

RAID0: It is called data striping. RAID0 split data among the multiple disk to increase the performance. An individual data read from the multiple disk to increase performance and write the data on different disks to increase read write speed.It does not provide any redundancy while one of the disks is failed there will be a chance of data lose.

Advantage:Increase the performance.

Drawback: does not provide redundancy.

RAID1: It is called data mirroring because it read write the identical data among the multiple disks. While one disk is failure we can retrieve data from the other working disk. So it provides redundancy .while we replace the new disk in the place of failure disk data will automatically sync with each other.

Advantage: It provides redundancy as well as fault tolerance.

Drawback: gets less usable capacity.

RAID5: It is called striping with parity because it strip the data among the multiple disk to increase the performance just like RAID0 and also store the parity information to retrieve the data in case of failure any disk. When a disk is gone bad it uses the parity information to retrieve the data.

Advantage: Fault tolerance and good performance.

Drawback: Lower performance due to parity overhead.

RAID6: It is called striping with double parity. It store extra parity block to increase the fault tolerance than RAID5.

Advantage: Fault tolerance and good performance.

Drawback: Lower performance due to parity overhead.

RAID10: It is combination of RAID0(data striping) for increased performance and RAID1(data mirroring) for high redundancy.

Advantage: It provides high performance and high redundancy.

Drawback: gets less usable capacity .

Configure Cisco ASA security level with practical example

November 09, 2018 Add Comment Edit

Configure Cisco ASA security level with practical example

In the previous article we learned about about what is security level of cisco ASA firewall ,different types of security levels, different types of security zones and in this article we learn how to configure cisco ASA firewall security level and check the traffic from the interface.

Explain Cisco ASA security level with practical example

Types of Cisco ASA security levels

There are three types of security levels.

Security level 100 is the highest security level on the Cisco ASA firewall and by default it it assigned the inside interface of the cisco ASA firewall. As it has highest security level traffic from internal network can roam any where. As security level is higher for the inside zone than the other zone thus traffic from the inside zone move to the DMZ zone as well outside zone.

Security level 0 is the lowest security level on the cisco ASA firewall and by default it is assigned to the outside interface of the cisco ASA firewall. As it is lowest security level traffic from the outside interface can not reach the internal network unless we apply policy within the access-list. For the outside zone security level is lower than inside zone as well as DMZ zone therefore traffic from the outside zone can not move to inside zone as well as DMZ zone.

Security level<1-99> is the another security level you can create any security level. Lets take an example suppose we create a DMZ zone and give one security level which is 50.traffic from the DMZ zone move to outside interface as dmz security level is higher than outside security level and traffic from the inside interface move to DMZ zone because inside security level is higher than DMZ level but traffic from the DMZ zone can not reach to inside interface because inside interface has security level which is higher the security level of DMZ zone.

When we are going to configure security level of cisco ASA firewall security level 100 is automatically set for the inside zone and security level 0 is assigned for the DMZ zone and outside zone. We manually configured DMZ security level 50 to configure cisco ASA firewall.

Lab Diagram

Configure Cisco ASA security level with practical example

From the above diagram we configure cisco ASA firewall security level. Suppose in the inside zone we have network 192.168.3.0/24 , in the dmz zone we have network 192.168.4.0/24 and in the outside zone we have network 192.168.5.0/24.

How to Configure Cisco ASA security level

To configure cisco ASA security level we need to configure the interface using below commands.

For inside zone

Ciscoasa (config)#interface E0/0

Ciscoasa(config-if)#nameif INSIDE

Ciscoasa(config-if)#ip address 192.169.3.2 255.255.255.0

Ciscoasa(config-if)#no shutdown

For DMZ zone

Ciscoasa (config)#interface E0/1

Ciscoasa(config-if)#nameif DMZ

Ciscoasa(config-if)#ip address 192.169.4.2 255.255.255.0

Ciscoasa(config-if)#no shutdown

For outside zone

Ciscoasa (config)#interface E0/2

Ciscoasa(config-if)#nameif OUTSIDE

Ciscoasa(config-if)#ip address 192.169.5.2 255.255.255.0

Ciscoasa(config-if)#no shutdown

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