Category Archives: Linux

Create Partition on New Disk using Parted on CentOS


Scenario: Create partition and Volume Group 60GB size from 100GB disk on new disk using Parted on CentOS
System: CentOS/RHEL 6 or 7

Steps:
Show new disk:
# fdisk -l | grep sd

[root@server ~]# fdisk -l | grep sd
Disk /dev/sda: 64.4 GB, 64424509440 bytes, 125829120 sectors
/dev/sda1   *        2048     2099199     1048576   83  Linux
/dev/sda2         2099200    81797119    39848960   8e  Linux LVM
Disk /dev/sdb: 107.4 GB, 107374182400 bytes, 209715200 sectors
[root@server ~]#

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Mount Windows Folder Sharing on RHEL 6/CentOS 6

Scenario:
-Mount Windows Folder Sharing (CIFS) on RHEL 6/CentOS 6.
-Set only Linux user >> user1 that have RWX access.
-Hide sharing credentials from other Linux users.
-Mount permanent at boot.

System: CentOS 6

Steps:
1) Edit /etc/fstab
# vi /etc/fstab
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Setup Virtual Domain Postfix

Scenario:
– Forward certain email recipient to another email address.
– Forward local Unix account email address to another email recipient because in the Postfix server don’t have mailbox.

System:
Postfix on CentOS 7/RHEL 7 (also work on CentOS 6/RHEL 6)

Steps:
– Edit main.cf
# vi /etc/postfix/main.cf
Edit the below parameter.

virtual_alias_domains = example1.com,example2.com
virtual_alias_maps = hash:/etc/postfix/virtual

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Setup Ethernet Bonding on RHEL 6

Scenario: Configure 4 ethernet into 2 ethernet bond0 and bond1 on RHEL 6/CentOS 6.
System: RHEL 6.9

Steps:
1) Create new file bond0 (Eth0+Eth1) with IP Address = 172.16.10.70
# vi /etc/sysconfig/network-scripts/ifcfg-bond0

DEVICE=bond0
IPADDR=172.16.10.70
NETMASK=255.255.255.0
TYPE=Bond
ONBOOT=yes
NM_CONTROLLED=no
BOOTPROTO=none
USERCTL=no
PEERDNS=yes
IPV6INIT=no

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Command to re-read new VM disk CentOS 6/RHEL 6

System: CentOS 6.9

Case:
Added new VM disk in CentOS 6 not showing the new VM disk when run fdisk -l.

Resolution:
Login as root, run this command to re-read the new VM disk without reboot the server.

ls /sys/class/scsi_host/ | while read host ; do echo "- - -" > /sys/class/scsi_host/$host/scan ; done

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Setup Banner on Console and Remote login CentOS/RHEL 6

Example add below banner.


********************************************************************
*                                                                  *
* This system is for the use of authorized users only.  Usage of   *
* this system may be monitored and recorded by system personnel.   *
*                                                                  *
* Unauthorized access to this machine is prohibited                *
* Press Ctrl+D if you are not an authorized user                   *
*                                                                  *
* Anyone using this system expressly consents to such monitoring   *
* and is advised that if such monitoring reveals possible          *
* evidence of criminal activity, system personnel may provide the  *
* evidence from such monitoring to law enforcement officials.      *
*                                                                  *
********************************************************************

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Command to re-read added new VM disk that not showing real size CentOS 6

System: CentOS 6.9

Case:
– User request in ESXi to add new 30 GB VM disk(2nd disk it mean sdb) but accidentally wrong added VM disk only 10 GB,after remove the 10 Gb and added 30 GB when run fdisk -l still showing 10 GB VM disk size.

Resolution:
Login as root, run this command to re-read the new disk size without reboot the server.

# echo 1 > /sys/block/sdb/device/rescan

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Increase or Decrease LV Swap in CentOS 6/RHEL 6

Scenario: How to increase or decrease swap space(logical volume swap) in CentOS 6/RHEL 6

System: CentOS 6/ RHEL 6

Steps increase Swap space
Example increase 1 GB swap space.

1) You must check the path of swap logical volume and the free space in the swap volume group before continue to step 2.
# free -m
# lvdisplay | grep swap
# vgs

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Fixing Postfix error unknown user name value: nobody

System: RHEL 6.9

Just got complain from App support Postfix was error.
Check on /var/log/maillog show this error
postfix[2319]: fatal: file /etc/postfix/main.cf: parameter default_privs: unknown user name value: nobody

The solution I did,check on /etc/passwd and found the user nobody in comment state.
Uncomment nobody and Postfix can start again.

# vi /etc/passwd
Uncomment nobody

# service postfix restart