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


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

               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


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.


[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)
p
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
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


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
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


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
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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