June 2017 - Linux Book Center

Configuring SAMBA Server in RHEL7/ Cent OS 7

We are going to learn how to configure SAMBA Server in RHEL7 / Cent OS 7. Its used to share file and printer sharing over the network.

Now a days its used as Domain controller like Windows Active Directory.

Will integrate SAMBA Server with Windows Domain as a Primary domain controller or as a domain member.

Operating System: RHEL7
Host Name: server
IP Address: 192.168.43.226 / 255.255.255.0

Port numbers for Samba server :

137/tcp
137/udp
138/tcp
138/udp
139/tcp
139/udp
445/tcp
445/udp

Daemons:

smbd: This is for file and printer sharing services
nmbd: This is for NetBIOS to IP Address service and Mapping NetBIOS Compluter Name to the TCP/IP IP Addresses.

Installing SAMBA Server:

#yum install –y samba samba–commons cups–libs policycoreutils–python samba–client

Below command will install all the packages which is required for samba server configuration.

 [[email protected] ~]# yum install -y samba

Create directory for sharing:

[[email protected] ~]# mkdir /sharedir

Create a new group called samba

#groupadd samba

 [[email protected] ~]# groupadd samba

change the group and permission for the directory which we are going to share using samba

[[email protected] ~]# chgrp -R samba /sharedir
[[email protected] ~]# chmod -R 777 /sharedir

check for the existing group and permission details for the directory.

[[email protected] ~]# ll / | grep sharedir
drwxrwxrwx. 2 root samba 6 Nov 11 08:59 sharedir

Now change the group and permission for the directory

Now again check for the group and permission for the directory and it’s changed.

Create a new user called test and add it to our newly created group which is called samba. Then set the samba password for the user.


[[email protected] ~]# useradd smbuser
[[email protected] ~]# usermod -G samba smbuser
[[email protected] ~]# smbpasswd -a smbuser
New SMB password:
Retype new SMB password:
Added user smbuser.

For samba default configuration file is /etc/samba/smb.conf

We are going to edit this configuration file. Before that its advisable to take backup of configuration file.

#cp -p /etc/samba/smb.conf /etc/samba/smb.conf.bkp

now we will edit the smb.conf file

[[email protected] ~]# vi /etc/samba/smb.conf

make the below entries at end of line.

Comment: This will explain the operation what we are doing like sharing directory or sharing printer.

Path: We are going to share a directory. So, here we should mention the directory with absolute path

Valid users: Here we can mention the users and groups who has permission to access this directory.

Writeable: i am giving yes, because i need read and write both permission.

browseable: If you want to access the shared things using browser, we can make it as yes

Public: We are not going to share this directory for all users. So, we should use no option.

[sharedir]
 comment = shared-directory
 path = /sharedir
 valid users = smbuser, @samba
 writeable = yes
 browseable = yes
 read only = no
 inherit acls = Yes

In the same smb.conf file we should add our interface name and IP Address to allow the network in samba server.

And one more entry is very important that we need to mention our windows machines workgroup name. First we will use default one. If the windows machines are falling under different workgroup name. Then we have to change the workgroup name in this configuration file.

WORKGROUP = MYGROUP

We can add the services in /etc/services file.

[[email protected] ~]# vi /etc/services
netbios-ns 137/tcp # netbios name service
netbios-ns 137/udp # netbios name service
netbios-dgm 138/tcp # netbios datagram service
netbios-dgm 138/udp # netbios datagram service
netbios-ssn 139/tcp # netbios session service
netbios-ssn 139/udp # netbios session service

Now start the samba service and enable the service permanently on this run level.

[[email protected] ~]# systemctl start smb.service
[[email protected] ~]# systemctl enable smb.service
Created symlink from /etc/systemd/system/multi-user.target.wants/smb.service to /usr/lib/systemd/system/smb.service.

Same like that start and enable nmb service.

#systemctl start nmb.service
#systemctl enable nmb.service

Add the firewall rule to allow the samba service via firewall.
In RHEL 7 firewall has been shipped from iptables to firewalld.

[[email protected] ~]# systemctl start firewalld
[[email protected] ~]# firewall-cmd --permanent --add-rich-rule='rule family="ipv4" source address="192.168.56.0/24" service name="samba" log prefix="samba" level="info" limit value="1/m" accept'
success
[[email protected] ~]# systemctl enable firewalld Created symlink from /etc/systemd/system/dbus-org.fedoraproject.FirewallD1.service to /usr/lib/systemd/system/firewalld.service.
Created symlink from /etc/systemd/system/basic.target.wants/firewalld.service to /usr/lib/systemd/system/firewalld.service.

Then reload the firewall configuration using below command

[[email protected] ~]# firewall-cmd --reload
success

Now all the configuration has been completed and will check in windows machine whether the samba is working well or not.

Connecting SAMBA server from linux client machine.

samba client should be installed in linux client machine.

Package: samba-client-4.4.4-9.el7.x86_64

#yum install samba-client*

[[email protected] ~]# smbclient -L 192.168.43.126 -U test

-L : This option will list the shared directories
192.168.43.226 : IP Address of samba server
-U : Option to mention the user name next to this which has access to this shared directory.

Output should be like below

Accessing via samba console:

#smbclient //192.168.43.226/sharedir -U test

above command will help you to show the content of shared directory and to do operations over their.

We successfully configure SAMBA server. Thanks for the support.

Configuring DHCP Server in RHEL7/ Cent OS 7

DHCP – Dynamic host configuration protocol

We are going to configure DHCP Server in RHEL7

It’s a network protocol used to assign IP’s to the client dynamically over the network.

DHCP Workflow:

Required Package installation:

#yum install dhcp

Now we should assign a insterface in DHCPDARGS in /etc/sysconfig/dhcpd

 [[email protected] ~]# vi /etc/sysconfig/dhcpd
 
  DHCPDARGS=enp0s3

After installing package it will create one empty configuration file /etc/dhcp/dhcpd.conf and we have one sample configuration file under /usr/share/doc/dhcp-4.2.15/dhcpd.conf.exmaple.

So as first, append the content from example file to original file using cat command.

[[email protected] ~]# cat /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example >> /etc/dhcp/dhcpd.conf

Open the configuration file to configure DHCP Server:

First will give basic configuration which will be common for your network.

[[email protected] ~]# vi /etc/dhcp/dhcpd.conf

Make the below entries

 option domain-name "lbcdomain.com";
 option domain-name-servers server.lbcdomain.com;
 default-lease-time 600;
 max-lease-time 7200;
 authoritative;
 log-facility local7;

Now make subnet details in same configuration file.

subnet 192.168.1.0 netmask 255.255.255.0 {
 option routers 192.168.1.254;
 option subnet-mask 255.255.255.0;
 option domain-search "lbcdomain.com";
 option domain-name-servers 192.168.1.1;
 option time-offset -18000; # Eastern Standard Time
 range 192.168.1.10 192.168.1.100;
}

Optional(To reserve IP for a dhcp client machine) :

If you wan to assign a static IP to a client using DHCP service, use the below command.

host station1 {
 option host-name "node11.lbcdomain.com";
 hardware ethernet 00:12:2A:2B:3C:AB;
 fixed-address 192.168.1.100;
}

Restart the dhcp service now to complete the DHCP server configuration.

[[email protected] ~]# systemctl restart dhcp

To check dhcp we should login in client machine which is in same network physically and edit the interface configuration file to make dhcp ip assigned.

#vi /etc/sysconfig/network-scripts/ifcfg-eth0

change the entry for BOOTPROTO as dhcp

DEVICE=eth0

BOOTPROTO=dhcp

TYPE=Ethernet

ONBOOT=yes

Save and quit.

Now restart the network service.

 #service network restart

now check for the ip and it should be assigned in between 192. 168.1.50 to 192.168.1.254

DHCP Configuration has been done.

Do practice well. All the best.

Bash Shell Script – 2

Today we are going to see how to use if statement in bash shell scripting.

before going to work with if statement, we should know the options which will be used in if statement to compare conditions.

-gt : greater than
-lt : less than
-eq : equal too
-ge : greater than or equal
-le : less than or equal

We are going to see a script with a simple if statement.

From the below script we are going to check given number is equal to 100 or not and using read command to get keyboard interaction while running the script.
It will read the number from our keyboard interaction and store it in a variable called number. Then will check for the condition, which we mentioned in if statement and display the string.

create a file called ifstat.sh using vi

#vi ifstat.sh

#!/bin/bash
echo “Enter a numeric value”
read number
if [ $number -eq 100 ]
then
echo “Numeric value is 100”
else
echo “Numeric values is not equal to 100”
fi

We can use elif, if we need to execute more than one statement for if condition.

For the same numeric value validation we are going to change use this elif option.

#vi ifstat1.sh

#!/bin/bash
echo “Enter a numeric value”
read number
if [ $number -eq 100 ]
then
echo “Numeric value is 100”
elif [ $number -gt 100 ]
then
echo “Numeric values is greater then 100”
elif [ $number -lt 100 ]
then
echo “Numeric values is less then 100”
fi

and we have nested if statement to validate the sme numeric values.
nested if is nothing but we are using if statement inside of if statement.

#vi ifstat2.sh

#!/bin/bash
echo “Enter a numeric value”
read number
if [ $number -eq 100 ]
then
echo “Numeric value is 100”
else
if[ $number -gt 100 ]
then
echo “Numeric values is greater then 100”
else
echo “Numeric values is less then 100”
fi
fi

Working with firewalld in RHEL 7/ Cent OS 7

First we make sure the firewall service is running before going to do any work related to ports.

Use the command to check the firewall service status:

[[email protected] ~]# systemctl status firewalld
● firewalld.service - firewalld - dynamic firewall daemon
 Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled; vendor preset: enabled)
 Active: active (running) since Sun 2017-10-29 08:46:09 IST; 4min 23s ago
 Docs: man:firewalld(1)
 Main PID: 523 (firewalld)
 CGroup: /system.slice/firewalld.service
 └─523 /usr/bin/python -Es /usr/sbin/firewalld --nofork --...

Oct 29 08:46:07 server systemd[1]: Starting firewalld - dynamic fir....
Oct 29 08:46:09 server systemd[1]: Started firewalld - dynamic fire....
Hint: Some lines were ellipsized, use -l to show in full.

Now we came to know that currently firewall is running and will check what are all the zone’s available and in public zone what are all the ports enabled/Listening, using below commands.

Command to check the available zone’s:


[[email protected] ~]# firewall-cmd --get-zones
work drop internal external trusted home dmz public block

Command to check the listening ports in public zone:

 [[email protected] ~]# firewall-cmd --zone=public --list-all
public (active)
 target: default
 icmp-block-inversion: no
 interfaces: enp0s8
 sources:
 services: dhcpv6-client mountd nfs rpc-bind ssh
 ports:
 protocols:
 masquerade: no
 forward-ports:
 sourceports:
 icmp-blocks:
 rich rules:

From the output we came to know that there are none ports enabled. So, will see how to enable a port.

For example i’m going to show you how to enable 8080(TCP Traffic) port.

[[email protected] ~]# firewall-cmd --zone=public --add-port=8080/tcp --permanent
success

–permanent: This is used to make the change permanent after rebooting the system.

–zone=public: We are enabling the port in public zone.

–add-port=8080/tcp: port number which we are going to enable.

We must reload the firewall configuration to make the changes effect in current session. However it will take the effect by next booting.

[[email protected] ~]# firewall-cmd --reload
success

Again will check for the enabled ports status in public zone after this changes.

[[email protected] ~]# firewall-cmd --zone=public --list-all
public (active)
 target: default
 icmp-block-inversion: no
 interfaces: enp0s8
 sources:
 services: dhcpv6-client mountd nfs rpc-bind ssh
 ports: 8080/tcp
 protocols:
 masquerade: no
 forward-ports:
 sourceports:
 icmp-blocks:
 rich rules:

It shows that 8080 port has been enabled.

I am going to show you how to remove the enabled port in firewall and as i said will reload the firewall configuration to make effect in this session. Then check for the status.

[[email protected] ~]# firewall-cmd --zone=public --remove-port=8080/tcp --permanent
success
[[email protected] ~]# firewall-cmd --reload
success
[[email protected] ~]# firewall-cmd --zone=public --list-all
public (active)
 target: default
 icmp-block-inversion: no
 interfaces: enp0s8
 sources:
 services: dhcpv6-client mountd nfs rpc-bind ssh
 ports:
 protocols:
 masquerade: no
 forward-ports:
 sourceports:
 icmp-blocks:
 rich rules:

We can get the list of zones where we have assigned interfaces and sources.

[[email protected] ~]# firewall-cmd --get-active-zone
external
 interfaces: enp0s3
public
 interfaces: enp0s8

To get the which zone is associate with a interface. Here i’m taking enp0s3 interface for test.

[[email protected] ~]# firewall-cmd --get-zone-of-interface=enp0s3
external

Command to get the permanent configuration of a zone. Here i’m taking public zone to test.

[[email protected] ~]# firewall-cmd --permanent --zone=public --list-all
public
 target: default
 icmp-block-inversion: no
 interfaces:
 sources:
 services: dhcpv6-client mountd nfs rpc-bind ssh
 ports:
 protocols:
 masquerade: no
 forward-ports:
 sourceports:
 icmp-blocks:
 rich rules:

Command to get the default zone:

[[email protected] ~]# firewall-cmd --get-default-zone
public

Command to set the default zone:

[[email protected] ~]# firewall-cmd --set-default-zone=home
success

Docker installation in RHEL7/ Cent OS 7

We are going to see Docker installation in RHEL7/ Cent OS 7.

Docker packages are available for RedHat Servers and RHEL Atomic Host editions alone not for other workstations or other variants of RHEL.

In this installation method internet is mandatory.

Docker installation using native docker script is straight forward method. Using “curl” will install the docker. Before installing docker, first check curl package is installed on your system.

#curl –version

[[email protected] ~]# curl --version
curl 7.29.0 (x86_64-redhat-linux-gnu) libcurl/7.29.0 NSS/3.21 Basic ECC zlib/1.2.7 libidn/1.28 libssh2/1.4.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtsp scp sftp smtp smtps telnet tftp
Features: AsynchDNS GSS-Negotiate IDN IPv6 Largefile NTLM NTLM_WB SSL libz unix-sockets

Installing Docker using curl command

Use the below command to install the docker.

#curl -SSL https://get.docker.com/ | sh

Now will enable the docker permanently in this runlevel and will start docker.

Command to enable the docker in this runlevel

#systemctl enable docker

Command to start the docker

#systemctl start docker

command to check the docker status

#systemctl status docker

Command to restart the docker

#systemctl restart docker

Docker has been installed and now will check the docker installation here.

#docker run hello-world

Will list the new containers with below command

#docker ps -a

Bash Shell Script – 1

Bash shell scripting is collections of Linux commands in a single file and we should know where and when to use the command. Its mandatory to know all the basic commands for bash shell scripting.

Execute permission is must to run the script.

Using below command will add the execute permission to a file.

#chmod +x testscript.sh

Here am using testscript.sh file for simple script.

Now check using “ll” command whether the permission has been added or not.

#ll | grep -i testscript.sh

We can use three methods to execute the bash shell script.

1. ./testscript.sh
2. sh testscript.sh
3. bash testscript.sh

Here am writing script to display a string.
Echo command will do simple printing whatever we are giving with double quotes.

Already i have created testscript file using vi editor.

#vi testscript.sh

Now will write a script to display Current logged in user, date and Count of users logged in.
Use the vi editor to create script file.

#vi testscript1.sh

type the below set off commands to create this script.

Save and exit from the file.

change the permission using chmod command.

#chmod +x testscript1.sh

Now run the script and check for the output.

like above will create bash shell scripts for our requirements.
Will see some other examples in next post.

DNS Configuration on RHEL7/ Cent OS 7

Domain Naming System is a naming convention for computers, which is connected to the internet. Its not possible to remember all the web server IP Address. So, here its comes as a resolution for this. Because, It will translate from the IP Address to Name and Name to IP Address.

We are going to see how to setup DNS in RHEL 7 and Cent OS 7.

Requirement:

Host Name: server.linuxbookcenter.com
IP Address: 192.168.43.226

Packages:
1. bind
2. bind-utils

Installing bind packages:

[[email protected]]# yum -y install bind*

BIND Configuring:

We are going to configure the “/etc/named.conf” file for BIND configuration.
open the file using vi editor and comment out two lines like shown below. This lines allow your DNS to listen all the IP Address.

Add your network by modifying “allow-query” line in the named.conf file to all the computers to do name transition which connected in this network

#vi /etc/named.conf

[[email protected] ~]# vi /etc/named.conf 

options {
 #listen-on port 53 { 127.0.0.1; };
 #listen-on-v6 port 53 { ::1; };

 directory "/var/named";
 dump-file "/var/named/data/cache_dump.db";
 statistics-file "/var/named/data/named_stats.txt";
 memstatistics-file "/var/named/data/named_mem_stats.txt";

 allow-query { localhost; 192.168.43.226/24;};

And the zone file information will be available in “/etc/named/rfc1912.zones” file by default. Here we should modify the entry based on our requirement.

Note: This entry contains the forward and reverse zone file names.

This file location included in “/etc/named.conf” file. Find the below screenshot.

Now save and exit from the “/etc/named.conf” file.

Provide zone file information entry:

edit the “/etc/named.rfc1912.zones” file to provide the zone file information entries.

[[email protected] ~]# vi /etc/named.rfc1912.zones

And make the below entries or modify the existing one based on our requirement.

zone "localhost.localdomain" IN {
 type master;
 file "named.localhost";
 allow-update { none; };
};

zone "lbcdomain.com" IN {
 type master;
 file "fwd.lbcdomain.com.db";
 allow-update { none; };
};

zone "1.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.ip6.arpa" IN {
 type master;
 file "named.loopback";
 allow-update { none; };
};

zone "1.0.0.127.in-addr.arpa" IN {
 type master;
 file "named.loopback";
 allow-update { none; };
};

zone "226.43.168.192.in-addr.arpa" IN {
 type master;
 file "43.168.192.db";
 allow-update { none; };
};

Create and Configure the Zone files:

Default location for the zone file’s : /var/named

create a forward zone file with “fwd.lbcdomain.com.db” name.

[[email protected] named]# vi /var/named/fwd.lbcdomain.com.db

Provide the below entries to complete the forward zone configuration.

keywords for Zone Files

A – A record

NS – Name Server

MX – Mail for Exchange

CN – Canonical Name

$TTL 86400
@ IN SOA server.lbcdomain.com. root.lbcdomain.com. (
                            20171129 ; serial
                            3600     ; refresh
                            1800 ; retry
                            604800 ; expire
                            86400 ) ; minimum
;Name server info
@ IN NS server.lbcdomain.com.

;Name server Ip info
server IN A 192.168.43.226

;Mail exchanger
lbcdomain.com. IN MX 10 mail.lbcdomain.com.

;A - Record Hostname to IP Address
www IN A 192.168.43.10
mail IN A 192.168.43.15

;CNAME Record
ftp IN CNAME www.lbcdomain.com.

Save and exit from the file and create reverse zone file with the name of “43.168.192.db”

PTR – Pointer

SOA – Start of Authority

[[email protected] ~]# vi /var/named/43.168.192.db

make the below entries in reverse zone file like below.

$TTL 86400
@ IN SOA server.lbcdomain.com. root.lbcdomain.com. (
                        20171129 ; serial
                        3600 ; refresh
                        1800 ; retry
                        604800 ; expire
                        86400 ) ; minimum

;Name server info
@ IN NS server.lbcdomain.com.

;Reverse lookup info
226 IN PTR server.lbcdomain.com.

;PTR Record for IP to Hostname
10 IN PTR www.lbcdomain.com.
15 IN PTR mail.lbcdomain.com.

Save and exit from the file.

We completed all the configuration and we should restart the bind service.

[[email protected] ~]# systemctl restart named

Make it enabled in system startup.

[[email protected] ~]# systemctl enable named

Now login in any client system which is already connected in same network and make DNS entries in

/etc/resolv.conf file like below.

#vi /etc/resov.conf

Save and exit from the file and if NM is managing the network, make DNS entry in /etc/sysconfig/network-scripts/ifcfg-eth0

Note: In my infra i took this network adapter configuration file for this ifcfg-eth0. This might vary in your systems.

#vi /etc/sysconfig/network-scripts/ifcfg-eth0

Save and exit after making the entry and restart the network service.

#service network restart

Will check the DNS connection from the client to DNS servers using dig command. Use the below command to check forward lookup

#dig www.lbcomain.com

Will receive the below output if working good.

Check in reverse from IP to Hostname to confirm whether the reverse lookup is working fine not.

#dig -x 192.168.43.226

Output:

We completely done on DNS configuration now:)

Changing/ Recovering root user password in RHEL7/ Cent OS 7

We are going to see How to Changing/ Recovering root user password in RHEL7/ CentOS 7 in this post

Boot the system and wait for GRUB menu. On some Operating systems, you need to disturb the booting by pressing any keys in your system.

Highlight the first line which is pointing the Operating System entry like showed in the above image and press “e” key in your keyboard to edit manually.

Then will get the below screen.

Using up/down, left/right arrow keys move the cursor to the “rhgb quiet” which is in kernel line starting with “linux16”

Using delete/backspace keys manually delete “rhgb quiet” entry and append “init=/bin/bash” entry like below.

Than press Ctrl+x to reboot your OS with specified option. Once rebooted, will get a shell prompt without credentials.

check whether the root filesystem has been mounted or not.

Mount the root filesystem with RW permission.

Now issue the “passwd” command to recover/change the root password. It will ask for the new password and re-enter the password for confirmation. Once provided the new password will receive the “Authentication token successfully updated”

Relabel the SELinux content using below command.

Restart the machine using the below command.

Finally, we recovered the root password. Now will restart the machine and login with a new root password.

Changing hostname in RHEL7 / CentoS 7

Hostname is like labeling for Computers/ Other devices which is connected in internet/network.
hostname is used to identify/access the computers/devices easily in network.

Will see how to check and change the hostname in RHEL 7/ Cent OS 7

Using “hostname” command will check the existing hostname.

nmtui:

Will use this Network managet tool to set the hostname and it will edit the “/etc/hostname” in background.

Now the hostname has been changed from “localhost.localdomain” to “server.localdomain” and by issueing “hostname” command will check whether the change has been implemented or not. If the hostname still shows the “localhost.localdomain” old one, we should restart the hostnamed to force the change in hostnamectl.

Will check the hostname now.

Successfully hostname has been changed.

Failed to start docker.service: Unit not found / Installation of docker in RHEL7.x / CentOS 7.x

Will see how to fix Failed to start docker.service: Unit not found / Installation of docker in RHEL7.x / CentOS 7.x.

Docker is open source and it will help us to deploy applications over the Linux containers.
Docker CLI command line tool will help to manage the lifecycle management of image based containers.

Linux container will enable fast application deployment, simplest testing, troubleshooting and maintenance.

Check for the installed docker details and remove the docker which is already installed.