How To Fix “Device eth0 does not seem to be present, delaying initialization” Error

This Ethernet card error is normally occur on Linux operating system like CentOS, Red Hat Linux etc. When you try to up the Ethernet card it is showing you the above topic error.

So in this post, we will provide you the step by step solutions and troubleshoot all the issue related this error.

In the initial step, you will check which Ethernet card is down , for this you can run the "ifconfig -a" command. Using this command you can check how many internet card is present on the server and on which Ethernet card used IP address.

Let's suppose you are using eth0 on your machine, and if this Ethernet card not taking any ip address and now show on your device that means it is down right now, so please try to start Eth0 device as given below command.

[root@localhost]# ifup eth0

Device eth0 does not seem to be present, delaying initialization

If your internet card show such issue that means you have an issue with MAC address. So in this post I would explain you how to resolve such issue.

1. In this step, please check the MAC Addresses are set correctly or not. For checking this you need to go the network card directory "/etc/sysconfig/network-scripts"

[root@localhost]# cd /etc/sysconfig/network-scripts

[root@localhost]# cat ifcfg-eth0

HWADDR=”00:15:5D:00:91:91”

In the configuration file, you can see the current hardware address of eth0 card, I have show you only HWADDR entry of my eth0 file. In this directory you can see if other Ethernet card is present or not. In my Linux machine i have two Ethernet card , please find the below second Ethernet card MAC address.

[root@localhost]# cat ifcfg-eth1

HWADDR=”00:15:5D:00:91:90”

2. Now we will see which link is present on the system currently and which is not active, for this you can use the below command to check the status.

[root@localhost]# ip -o link

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN \    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

2: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP qlen 1000\    link/ether 00:15:5D:00:91:90 brd ff:ff:ff:ff:ff:ff

3: eth2: mtu 1500 qdisc   pfifo_fast state UP qlen 1000\ link/ether 00:15:5D:00:91:91 brd ff:ff:ff:ff:ff:ff

Here, no eth1 but there is an eth2 present on the system, so might be problem is that the eth0 is renamed to eth2 but we will confirm with below command.

[root@localhost]# dmesg | grep eth0

udev: renamed network interface eth0 to eth2

udev: renamed network interface rename3 to eth0

From this command it shows that udev rename the network interface, so in the next step we will remove the wrong entry and configure the Ethernet card 

3. Now please open the network rules file to confirm the mac address. Please open this file "/etc/udev/rules.d/70-persistent-net.rules" 

[root@localhost]# cat /etc/udev/rules.d/70-persistent-net.rules

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:90", ATTR{type}=="1", KERNEL=="eth*", NAME="eth1"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:91", ATTR{type}=="1", KERNEL=="eth*", NAME="eth2"

SUBSYSTEM=="net", ACTION=="add", DRIVERS=="?*", ATTR{address}=="00:15:5d:00:91:91", ATTR{type}=="1", KERNEL=="eth*", NAME="eth0"

Looks like there are multiple entries for the same MAC address. Removed the incorrect entry and restart the interface using below command.

[root@localhost]# ifup eth0

Now you eth0 card is up and if you are running "ifconfig -a" command you can see the eth0 card with mac address. 

Hope you are get the solution of the above issue, also please let me know if you have any other issue.

How to Create Local YUM Repository on CentOS 7 / RHEL 7

In this post, I describes how to setup a local Yum repository on CentOS 7 & RHEL 7 server operating system.

The local YUM repository is the most significant way to perform any type of package installation without any internet connection. If you have to install software, security updates and fixes often in multiple systems in your local network, then having a local repository is an efficient way. 

All required packages are downloaded over the fast LAN connection from your local server, so that it will save your Internet bandwidth and reduces your annual cost of Internet.

Now, please find the step by step method to create a YUM repository on RHEL 7 & CentOS 7.

Mount the Local Media:

In this step we mount our CentOS 7 / RHEL 7 installation DVD. For example, let us mount the installation media on /mnt directory.

#mount -o loop /dev/cdrom /mnt

In my Linux machine i will insert the ISO on cdrom and mount it on /mnt directory.

Copy or Extract the Media:

In this step, we will extract or copy iso files to local machine. For this work we will create a one mount point directory and copy all the packages files from /mnt.

#mkdir /centos

#cp -rvf /mnt/* /centos

So all the packages are copied on the "/centos" directory.

Install repository packages:

In this step, we will create repository but before this we need to install the "createrepo" rpm on the YUM server.

For createrepo, you need to install some dependency rpm which are listed in "Packages" folder.

#rpm -ivh libxml2-python-2.9.1-5.el7_0.1.x86_64.rpm

#rpm -ivh python-deltarpm-3.6-3.el7.x86_64.rpm

#rpm -ivh deltarpm-3.6-3.el7.x86_64.rpm

#rpm -ivh createrepo-0.9.9-23.el7.noarch.rpm

Once these required packages is installed we create the repo using createrepo command.

#createrepo -v /centos/Packages

Remove the Online Repository:

Please remove the old repository from /etc/yum.repos.d directory. In this directory all the default local centOS / RHEL repository are exist.

#rm -rf /etc/yum.repos.d/*

Create Local Repository:

In this step we will create the local repostiory which is always kept as a local. Using this local repo we can install all the packages and their dependency.

#vi /etc/yum.repos.d/local.repo

[Packages]

baseurl=file:///centos/Packages

gpgcheck=0

enable=1

After save the file your local.repo repository has been created. In next step we will enable it.

Enable Local Repository:

After successfully creation of YUM repository we will enable it.

#yum clean all

#yum repolist all

Using this repolist command you can check the newly created and existing repository on the server. After that you can easily install the pacakges using YUM in RHEL 7 & CentOS 7.

How to setup NFS Server on CentOS 7 / RHEL 7

In this post, I would explain you , how to setup NFS server on CentOS 7 & RHEL 7. This step by step installation and configuration method of NFS server is work in Fedora 22 version also.

Network File System is used for to share files and folders between Linux / Unix systems. NFS enables you to mount a remote share locally as well as it allows to have updated files across the share.

Before starting the setup method , we need to understand which service and files are used for NFS setup.

Please find the below services which are used for NFS setup. its must be always runs on operating system.

rpcbind service: The rpcbind server is used to converts RPC program numbers into universal addresses.

nfs-server service:  Its enables the NFS clients to access NFS shares.

nfs-lock / rpc-statd service: these are the recovery services when an NFS server crashes and reboots.

nfs-idmap service: It translates user and group ids into names, and to translate user and group names

into ids.

The mail configuration file for NFS server and client is "/etc/exports". It controls which file systems are exported to remote hosts and specifies options.

Now, we will start the step by step process for setup of NFS server on CentOS 7 / RHEL 7.

NFS Server Setup:

1. First we need to install the NFS packages on the server where we want to setup of NFS server. We can install the required NFS packages using YUM.

#yum install nfs-utils libnfsidmap

It's installed all the required packages on NFS server.

2. Once the packages are installed we will enable and start all the above services which we explain in my post.

#systemctl enable rpcbind

#systemctl enable nfs-server

#systemctl start rpcbind

#systemctl start nfs-server

#systemctl start rpc-statd

#systemctl start nfs-idmapd

You can check the status of all these service by using this command "systemctl status service_name" to ensure all are working fine.

3. Now we will created the shared directory which we want to share for client.

#mkdir /backup

#chmod -R 777 /backup

We can change the permission of NFS folder as per your requirement. In my case I'll provide the read write permession to all NFS client on this shared folder, so they can easily copy and remove the files. Ideally for security purpose we never provide 777 permission.

4. In this step we will make an entry of shared folder and client information , what permission we give to client to access the folder and which client can access the NFS shared folder.

# vi /etc/exports

/backup 10.135.0.27(rw,sync,no_root_squash)

In above command output, you can see the "/backup" is shared NFS server folder and "10.135.0.27" user client have rights to access this shared folder.

Also in brackets if you see the permission parameter which is very important when we setup the NFS setup. Please find the small idea about these permission parameteres.

rw: Writable permission to shared folder

sync:  all changes to the according filesystem are immediately flushed to disk.

no_root_squash: By default, any file request made by user root on the client machine is treated as by user nobody on the server. If no_root_squash is selected, then root on the client machine will have the same level of access to the files on the system as root on the server

5. Now, we will export the shared directories using following command.

# exportfs -r

We can use other syntax as well for this, which is listed below.

exportfs -v : Displays a list of shares files and export options on a server
exportfs -a : Exports all directories listed in /etc/exports
exportfs -u : Unexport one or more directories
exportfs -r : Reexport all directories after modifying /etc/exports

6. Now in above step 5, we configured and installed the NFS server but if firewall is running on your machine then we need to add NFS services in firewall as well.

#firewall-cmd --permanent --zone public --add-service mountd
#firewall-cmd --permanent --zone public --add-service rpc-bind
#firewall-cmd --permanent --zone public --add-service nfs
#firewall-cmd --reload

NFS Client Steup:

1. Once we installed the NFS server, now we will mount the remote file system on NFS client machine. So for this , on client machine we will install the same NFS packages which we installed during NFS server setup.

#yum install nfs-utils libnfsidmap

It's installed all the required packages on NFS client. Once the packages is installed on NFS client machine we will start the "rpcbind" services on client machine.

#systemctl enable rpcbind

#systemctl start rpcbind

2. Now we will mount the NFS shared folder on client machine but before doing that we will check on client machine which NFS server is available.

client# showmount -e 10.135.0.27    (10.135.0.2 is myserver machine IP)

Export list for 10.135.0.27:

/backup      10.135.0.2

So you can able to see on client machine our NFS shared folder is available on 10.135.0.27 NFS server. 

3. In this step , now we will mount this NFS shared folder on NFS client machine, for this we will create a mount point on client machine where we mount the server shared folder.

client# mkdir /mnt/backup

client#mount 10.135.0.27:/backup /mnt/backup

So you can check the mount folder using "df -h" command.

4. To make a permanent entry on client machine so that once you take a reboot of client machine , the shared folder is not umount.

client# vi /etc/fstab

10.135.0.27:/backup/ /mnt/backup nfs rw,sync,hard,intr 0 0

Please make an entry permanent on client machine and save it and take a restart of machine , after reboot once you login you will see the shared folder still available on the client machine.

5. For testing of shared folder, you can create a one file on client machine then check on the server this newly created file is shown on the server folder also.

So, using all these steps you can easily setup the NFS server and client on your machine.

How To Install VNC Server On CentOS 7 & RHEL 7

In this post, you can find the step by step method of installation and configuration of VNC server on CentOS 7 / RHEL 7. VNC server installation on CentOS 7 / RHEL 7 is quite different from older version of linux.

Before moving to installation part, first we need to know what is VNC server and how it is works on Linux environment.

VNC (Virtual Network Computing):

VNC stands for Virtual Network Computing server which allows for remote desktop connection in graphical GUI mode by using their remote client. For VNC client we can use VNC viewer. We can use other VNC client as wll for taking a remote connection of VNC server.  Some packages is required for installation and configuration which we explain during the post.

Step by Step Installation and Configuration method for VNC Server:

First we need to install the required packages on the server. You can install the packages using "YUM" command and if you have source package you can install it. On my machine I have yum repo , so we can install the rpm using YUM.

1. In my machine I am using GNOME desktop, if GNOME desktop is not installed on your machine then you need to install it by using below command.

#yum groupinstall "GNOME Desktop"

Using above command you can install all the packages which are required for desktop version. When you run the above command you can see all listed packages before installation.

2. After installation of GNOME packages we will install tigervnc-server packages which is mandatory for VNC server installation.

#yum install tigervnc-server*

here, "*" sign is used for all dependency, if you use this sign it is automatically installed all dependency. Using above command we can install all the VNC server rpm's.

3. Now we will add VNC user on the server.

#useradd vibhor

In my case I used my name but you can use any name.

4. In CentOS 7,there is change in the vncserver configuration file, becuase in older version of CentOS it was /etc/sysconfig/vncservers and now it have changed in /lib/systemd/system/vncserver@.service

#cp /lib/systemd/system/vncserver@.service /etc/systemd/system/vncserver@:2.service

5. Now we will edit the vncserver file as describe below.

#vi /etc/systemd/system/vncserver@:2.service

[...]

[Service]

Type=forking

# Clean any existing files in /tmp/.X11-unix environment

ExecStartPre=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'

#ExecStart=/sbin/runuser -l <USER> -c "/usr/bin/vncserver %i"

#PIDFile=/home/<USER>/.vnc/%H%i.pid

ExecStart=/sbin/runuser -l vibhor -c "/usr/bin/vncserver %i"

PIDFile=/home/vibhor/.vnc/%H%i.pid

ExecStop=/bin/sh -c '/usr/bin/vncserver -kill %i > /dev/null 2>&1 || :'

In the above file, you need to set the user name which use add on the server for access the VNC server. You can add more user on the server but for each user you need to create new service file and in each file you will change the user string.

6. If your firewall is enable on your machine then you need to add VNC server service on the firewall and make a permanent, in my machine it is enable so i will use it.

#firewall-cmd --permanent --zone=public --add-service vnc-server

#firewall-cmd --reload

7.  Now please switch the user from root and start the vnc server for vnc user.

#su - vibhor

vibhor@localhost~]$ vncserver

You will require a password to access your desktops.

Password:<--yourvncpassword

Verify:<--yourvncpassword

xauth:  file /home/vibhor/.Xauthority does not exist

New 'localhost:2 (vibhor)' desktop is localhost:2

Creating default startup script /home/vibhor/.vnc/xstartup

Starting applications specified in /home/vibhor/.vnc/xstartup

Log file is /home/vibhor/.vnc/localhost:2.log

It is creating the file in your home direcotory , if you see the service is startup and working fine.

8. Now please start the all required services for vnc server and make it permanent so once you take a reboot of machine it is not disable. All the service start and enable through root user.

#systemctl daemon-reload

#systemctl enable vncserver@:2.service

#systemctl start vncserver@:2.service

9. Now  go to your workstation or laptop and install the VNC client and connect the server using "vibhor" vnc user. when you run the client it is asking for host name so you will enter the host name and enter the vncuser password after that you can connect the server graphically.

How to add a fake dummy null printer in centos 7

Please find the below step by step simple method to add tge fake , dummy or Null printer on Centos7

1. Install the rpm packages for configuration of printer

#yum install system-config-printer*

2. Install cups printer packages

#yum install cups*

3. start the cups services on the centos 7

# systemctl status cups

cups.service - CUPS Printing Service

   Loaded: loaded (/usr/lib/systemd/system/cups.service; enabled; vendor preset: enabled)

   Active: inactive (dead)

# systemctl restart cups

# systemctl status cups

cups.service - CUPS Printing Service

   Loaded: loaded (/usr/lib/systemd/system/cups.service; enabled; vendor preset: enabled)

   Active: active (running) since Mon 2017-01-23 09:23:11 GMT; 4s ago

 Main PID: 6121 (cupsd)

   CGroup: /system.slice/cups.service

           └─6121 /usr/sbin/cupsd -f

Jan 23 09:23:11 linux systemd[1]: Started CUPS Printing Service.

Jan 23 09:23:11 linux systemd[1]: Starting CUPS Printing Service...

Please add below line in cupsd.conf if doesn't exist.

# vi /etc/cups/cupsd.conf

FileDevice yes

Command to add a printer-

# lpadmin -p myprinter -E -v file:///dev/null

To check the default printer status-

# lpstat -s

no system default destination

device for myprinter: ///dev/null

ifconfig command not found in centos 7 minimal installation

By default in Centos 7 minimal installation , ifconfig command is not found, so for obtenining this command , first you need to check which packages yum provide for this.

[root@localhost]# yum provides ifconfig

Loaded plugins: fastestmirror
Repository 'Packages' is missing name in configuration, using id
Loading mirror speeds from cached hostfile
Packages/filelists_db                                                                                                                              
No matches found

Note: here no packages is installed on the system.

So, using yum we will install the net-tool rpm which is required for ifconfig command

[root@localhost]# yum install net-tools*

Loaded plugins: fastestmirror
Repository 'Packages' is missing name in configuration, using id
Loading mirror speeds from cached hostfile
Resolving Dependencies
--> Running transaction check
---> Package net-tools.x86_64 0:2.0-0.17.20131004git.el7 will be installed
--> Finished Dependency Resolution

Dependencies Resolved

 Package                  Arch           Version                                   Repository                    Size

Installing:
 net-tools                x86_64         2.0-0.17.20131004git.el7         Packages                        304 k

Transaction Summary
========================================================================
Install  1 Package

Total download size: 304 k
Installed size: 917 k
Is this ok [y/d/N]: y
Downloading packages:
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : net-tools-2.0-0.17.20131004git.el7.x86_64                                                                     1/1
Verifying  : net-tools-2.0-0.17.20131004git.el7.x86_64                                                                    1/1

Installed:
net-tools.x86_64 0:2.0-0.17.20131004git.el7

Complete!

Now run the ifconfig command after successfully installed the packages.

[root@localhost]# ifconfig -a
ens33: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 192.26.12.1  netmask 255.255.0.0  broadcast 192.26.255.255
        inet6 fe80::250:56ff:febf:f6  prefixlen 64  scopeid 0x20<link>
        ether 00:50:56:bf:00:f6  txqueuelen 1000  (Ethernet)
        RX packets 18939  bytes 1251073 (1.1 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 433  bytes 63109 (61.6 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 0  (Local Loopback)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0


[root@localhost]# yum provides ifconfig

Loaded plugins: fastestmirror
Repository 'Packages' is missing name in configuration, using id
Loading mirror speeds from cached hostfile
net-tools-2.0-0.17.20131004git.el7.x86_64 : Basic networking tools
Repo: @Packages
Matched from:
Filename: /usr/sbin/ifconfig