Configuring sudo Access

  1. Log in to the system as the root user.
  2. Create a normal user account using the useradd command. Replace USERNAME with the user name that you wish to create.
    # useradd USERNAME
  3. Set a password for the new user using the passwd command.
    # passwd USERNAME Changing password for user USERNAME. New password: Retype new password: passwd: all authentication tokens updated successfully.
  4. Run the visudo to edit the /etc/sudoers file. This file defines the policies applied by the sudo command.
    # visudo
  5. Find the lines in the file that grant sudo access to users in the group wheel when enabled.
    ## Allows people in group wheel to run all commands
    # %wheel        ALL=(ALL)       ALL
  6. Remove the comment character (#) at the start of the second line. This enables the configuration option.
  7. Save your changes and exit the editor.
  8. Add the user you created to the wheel group using the usermod command.
    # usermod -aG wheel USERNAME
  9. Test that the updated configuration allows the user you created to run commands using sudo.
    1. Use the su to switch to the new user account that you created.
      # su USERNAME -
    2. Use the groups to verify that the user is in the wheel group.
      $ groups USERNAME wheel
    3. Use the sudo command to run the whoami command. As this is the first time you have run a command using sudo from this user account the banner message will be displayed. You will be also be prompted to enter the password for the user account.
      $ sudo whoami We trust you have received the usual lecture from the local System Administrator. It usually boils down to these three things: #1) Respect the privacy of others. #2) Think before you type. #3) With great power comes great responsibility. [sudo] password for USERNAME: root
      The last line of the output is the user name returned by the whoami command. If sudo is configured correctly this value will be root.
You have successfully configured a user with sudo access. You can now log in to this user account and use sudo to run commands as if you were logged in to the account of the root user

Install SVN (Subversion) Server on Linux

Install SVN (Subversion) Server on Fedora 20/19, CentOS/Red Hat (RHEL) 6.5/5.10

This is guide, howto install SVN (Subversion) server on Fedora 20/19/18/17/16/15/14, CentOS 6.5/6.4/6.3/6.2/6.1/6/5.10, Red Hat (RHEL) 6.5/6.4/6.3/6.2/6.1/6/5.10.

What is SVN (Subversion)?
Subversion is a free/open-source version control system. Subversion manages files and directories, and the changes made to them, over time. This allows you to recover older versions of your data, or examine the history of how your data changed. In this regard, many people think of a version control system as a sort of “time machine”.

Install SVN (Subversion) Server on Fedora 20/19/18, CentOS 6.5/5.10, Red Hat (RHEL) 6.5/5.10

1. Change root user
su –
## OR ##
sudo -i

2. Install needed packages (mod_dav_svn and subversion)
#yum install mod_dav_svn subversion
Note: If you don’t have Apache installed already, this command installs it also. Read more about installing Apache and PHP >>

3. Modify Subversion config file /etc/httpd/conf.d/subversion.conf
Add following config to /etc/httpd/conf.d/subversion.conf file:
LoadModule dav_svn_module modules/
LoadModule authz_svn_module modules/

<Location /svn>
DAV svn
SVNParentPath /var/www/svn
AuthType Basic
AuthName “Subversion repositories”
AuthUserFile /etc/svn-auth-users
Require valid-user

4. Add SVN (Subversion) users
Use following command:

## Create testuser ##
htpasswd -cm /etc/svn-auth-users testuser
New password:
Re-type new password:
Adding password for user testuser

## Create testuser2 ##
htpasswd -m /etc/svn-auth-users testuser2
New password:
Re-type new password:
Adding password for user testuser2
Note: Use exactly same file and path name as used on subversion.conf file.

This example use /etc/svn-auth-users file.

5. Create and configure SVN repository
#mkdir /var/www/svn
#cd /var/www/svn

#svnadmin create testrepo
#chown -R apache.apache testrepo

## If you have SELinux enabled (you can check it with “sestatus” command) ## then change SELinux security context with chcon command ##

#chcon -R -t httpd_sys_content_t /var/www/svn/testrepo

## Following enables commits over http ##
#chcon -R -t httpd_sys_rw_content_t /var/www/svn/testrepo

#Restart Apache:
## Fedora ##
systemctl restart httpd.service
## OR ##
#service httpd restart

## CentOS / RHEL ##
/etc/init.d/httpd restart
## OR ##
service httpd restart

Goto http://localhost/svn/testrepo address and you should see something like following, write username and password:

SVN testrepo revision 0:

6. Configure repository
To disable anonymous access and enable access control add following rows to testrepo/conf/svnserve.conf file:

## Disable anonymous access ##
anon-access = none

## Enable access control ##
authz-db = authz

7. Create trunk, branches and tags structure under testrepo
Create “template” directories with following command:
#mkdir -p /tmp/svn-structure-template/{trunk,branches,tags}

Then import template to project repository using “svn import” command:
#svn import -m ‘Initial import’ /tmp/svn-structure-template/

Adding /tmp/svn-structure-template/trunk
Adding /tmp/svn-structure-template/branches
Adding /tmp/svn-structure-template/tags

Committed revision 1.
Check results on browser and see testrepo revision 1:

OpenLDAP Server Configuration on CentOS 7 / RHEL 7

OpenLDAP is an open-source implementation of Lightweight Directory Access Protocol developed by OpenLDAP project. LDAP is an Internet protocol that email and other programs use to look up contact information from a server. It is released under OpenLDAP public license; it is available for all major Linux distributions, AIX, Android, HP-UX, OS X, Solaris, Windows and z/OS.

It functions like a relational database in certain ways and can be used to store any information. LDAP is not limited to store the information; it is also used as a backend database for “single sign-on” where one password for a user is shared between many services.

We will configure OpenLDAP for centralized login where the users use the single account to log in on multiple servers.


Make sure both LDAP server “master.atlas.local” (192.168.xx.xx).

Make an entry for each machine in /etc/hosts for name resolution

vi /etc/hosts master.atlas.local server

Here I will use IP address for all the configuration.

Install the following LDAP RPM packages to get started. Run below command on LDAP server (master.atlas.local).

yum -y install openldap compat-openldap openldap-clients openldap-servers openldap-servers-sql openldap-devel

Start the LDAP service and enable it for the auto start of service on system boot.

#systemctl start slapd.service
#systemctl enable slapd.service

Verify the LDAP.

#netstat -antup | grep -i 389

tcp        0      0   *               LISTEN      1520/slapd
tcp6       0      0 :::389                  :::*                    LISTEN      1520/slapd

Setup LDAP root password:

Run below command to create an LDAP root password; we will use this root password throughout this article. So make a note of this and keep it aside.

[root@server ~]# slappasswd

New password:
Re-enter new password:

[root@server ~]#
Configure OpenLDAP server:

OpenLDAP servers configuration files are found in /etc/openldap/slapd.d/. To start with the configuration of LDAP, we would need to update the variables “olcSuffix” and “olcRootDN“.

olcSuffix –  Database Suffix, it is the domain name for which the LDAP server provides the information. In simple words, it should be changed to your domain name.

olcRootDN – Root Distinguished Name (DN) entry for the user who has the unrestricted access to perform all administration activities on LDAP, like a root user.

olcRootPW – Password for the above RootDN.

Please create a .ldif file and add the below entries.

# vi db.ldif
dn: olcDatabase={2}hdb,cn=config
changetype: modify
replace: olcSuffix
olcSuffix: dc=atlas,dc=local
dn: olcDatabase={2}hdb,cn=config

changetype: modify
replace: olcRootDN
dn: olcDatabase={2}hdb,cn=config
changetype: modify
replace: olcRootPW

Once you are done with the ldif file, send the configuration to the LDAP server.

ldapmodify -Y EXTERNAL  -H ldapi:/// -f db.ldif

Make a changes to /etc/openldap/slapd.d/cn=config/olcDatabase={1}monitor.ldif (Do not edit manually) file to restrict the monitor access only to ldap root (ldapadm) user not to others.

# vi monitor.ldif
dn: olcDatabase={1}monitor,cn=config
changetype: modify
replace: olcAccess
olcAccess: {0}to * by dn.base=”gidNumber=0+uidNumber=0,cn=peercred,cn=external, cn=auth” read by dn.base=”cn=ldapadm,dc=atlas,dc=local” read by * none

Once you have updated the file, send the configuration to the LDAP server.
ldapmodify -Y EXTERNAL  -H ldapi:/// -f monitor.ldif

Create LDAP certificate:

Let’s create a self-signed certificate for our LDAP server, below command, generates both certificate and private key in /etc/openldap/certs/ directory.

openssl req -new -x509 -nodes -out /etc/openldap/certs/Filenamecert.pem -keyout /etc/openldap/certs/Filenamekey.pem -days 365

Generating a 2048 bit RSA private key

writing new private key to ‘/etc/openldap/certs/Filenamekey.pem’
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank

For some fields there will, be a default value,

If you enter ‘.’, the field will be left blank.
Country Name (2 letter code) [XX]: XX
State or Province Name (full name) []: XX
Locality Name (eg, city) [Default City]: XXXXXX
Organization Name (eg, company) [Default Company Ltd]:MaddySystems
Organizational Unit Name (eg, section) []:IT Infra
Common Name (eg, your name or your server’s hostname) []:server.atlas.local
Email Address []

Set the owner and group permissions to ldap.
chown -R ldap:ldap /etc/openldap/certs/*.pem

Verify the created LDAP certificate under /etc/openldap/certs/.

ll /etc/openldap/certs/*.pem

-rw-r–r–. 1 ldap ldap 1440 Oct 10 02:31 /etc/openldap/certs/Filenameert.pem
-rw-r–r–. 1 ldap ldap 1704 Oct 10 02:31 /etc/openldap/certs/Filenamekey.pem

Create certs.ldif file to configure LDAP to use secure communication using a self-signed certificate.

# vi certs.ldif
dn: cn=config
changetype: modify
replace: olcTLSCertificateFile
olcTLSCertificateFile: /etc/openldap/certs/Filenamecert.pem
dn: cn=config
changetype: modify
replace: olcTLSCertificateKeyFile
olcTLSCertificateKeyFile: /etc/openldap/certs/Filenamekey.pem

Import the configurations to LDAP server.
ldapmodify -Y EXTERNAL  -H ldapi:/// -f certs.ldif

Verify the configuration:

slaptest -u
You should get the following message confirms the verification is complete.
config file testing succeeded

Set up LDAP database:

Copy the sample database configuration file to /var/lib/ldap and update the file permissions.
cp /usr/share/openldap-servers/DB_CONFIG.example /var/lib/ldap/DB_CONFIG

chown ldap:ldap /var/lib/ldap/*
Add the cosine and nis LDAP schemas.
ldapadd -Y EXTERNAL -H ldapi:/// -f /etc/openldap/schema/cosine.ldif
ldapadd -Y EXTERNAL -H ldapi:/// -f /etc/openldap/schema/nis.ldif
ldapadd -Y EXTERNAL -H ldapi:/// -f /etc/openldap/schema/inetorgperson.ldif

Generate base.ldif file for your domain.

# vi base.ldif

dn: dc=atlas,dc=local
dc: atlas
objectClass: top
objectClass: domain
dn: ,dc=atlas,dc=local
objectClass: organizationalRole
description: LDAP Manager

dn: ou=People,dc=atlas dc=local
objectClass: organizationalUnit
ou: People
dn: ou=Group,dc=atlas,dc=local
objectClass: organizationalUnit
ou: Group

Build the directory structure.

ldapadd -x -W -D “,dc=atlas,dc=local” -f base.ldif
ldapadd command will prompt you for the password of (LDAP root user).
Enter LDAP Password:

adding new entry “dc=atlas,dc=local”
adding new entry “,dc=atlas,dc=local”
adding new entry “ou=People,dc=atlas,dc=local”
adding new entry “ou=Group,dc=atlas,dc=local”

Let’s create an LDIF file for a new user called raj

vi raj.ldif

Paste the below lines to above LDIF file.

dn: uid=raj,ou=People,dc=atlas,dc=local
objectClass: top
objectClass: account
objectClass: posixAccount
objectClass: shadowAccount
cn: raj
uid: raj
uidNumber: 9999
gidNumber: 100
homeDirectory: /home/raj
loginShell: /bin/bash
gecos: Raj [Admin (at) AtlasSystems]
userPassword: {crypt}x
shadowLastChange: 17058
shadowMin: 0
shadowMax: 99999
shadowWarning: 7

Use the ldapadd command with the above file to create a new user called “raj” in OpenLDAP directory.

ldapadd -x -W -D “,dc=atlas,dc=local” -f raj.ldif
Enter LDAP Password:
adding new entry “uid=raj,ou=People,dc=atlas,dc=local”
Assign a password to the user.
ldappasswd -s password123 -W -D “,dc=atlas,dc=local” -x “uid=raj,ou=People,dc=atlas,dc=local”

-s specify the password for the username
-x username for which the password is changed
-D Distinguished name to authenticate to the LDAP server
Verify LDAP entries.

ldapsearch -x cn=raj -b dc=atlas,dc=local
# extended LDIF
# LDAPv3
# base <dc=atlas,dc=local> with scope subtree
# filter: cn=raj
# requesting: ALL
# raj, People, atlas.local
dn: uid=raj,ou=People,dc=atlas,dc=local
objectClass: top
objectClass: account
objectClass: posixAccount
objectClass: shadowAccount
cn: raj
uid: raj
uidNumber: 9999
gidNumber: 100
homeDirectory: /home/raj
loginShell: /bin/bash
gecos: Raj [Admin (at) AtlasSystems]
shadowLastChange: 17058
shadowMin: 0
shadowMax: 99999
shadowWarning: 7
userPassword:: e1NTSEF9MkE2eUhIS0pJQVRnMHBCdkpVWjR5Q3JvTkJLTzdBTWY=

# search result
search: 2
result: 0 Success
# numResponses: 2
# numEntries: 1
To delete an entry from LDAP (Optional).

ldapdelete -W -D “,dc=atlas,dc=local” “uid=raj,ou=People,dc=atlas,dc=local”


firewall-cmd –permanent –add-service=ldap
firewall-cmd –reload

Enable LDAP logging:

Configure Rsyslog to log a LDAP events to log file /var/log/ldap.log.
Add below line to /etc/rsyslog.conf file.

local4.* /var/log/ldap.log

Restart the rsyslog service.

systemctl restart rsyslog

LDAP client configuration to use LDAP Server:

Install the necessary LDAP client packages on the client machine.

# yum install -y openldap-clients nss-pam-ldapd

Execute the below command to add the client machine to LDAP server for single sign on. Replace “” with your LDAP server’s IP address or hostname.

# authconfig –enableldap –enableldapauth –ldapserver= –ldapbasedn=”dc=atlas,dc=local” –enablemkhomedir –update

Restart the LDAP client service.

# systemctl restart  nslcd

Verify LDAP Login:

Use getent command to get the LDAP entries from the LDAP server

# getent passwd raj

raj:x:9999:100:Raj [Admin (at) AtasSystem]:/home/raj:/bin/bash


Installing Java on Linux

Installing Java on Linux


Download the latest version of JDK from I have downloaded jdk-1_5_0_01-Linux-i586.bin for this tutorial.
Change to the directory where you downloaded the JDK ( I downloaded it in my home directory /home/maddy) and make the self-extracting binary executable:
chmod +x jdk-1_5_0_01-Linux-i586.bin

Run the self-extracting binary, this will display the License agreement text and will ask you to accept the agreement:
Above command should create a directory called jdk1.5.0_01 in the /home/maddy directory. Move the JDK directory to /opt . Here is the command used:
mv jdk1.5.0_01 /opt
Set the JAVA_HOME environment variable, by modifying /etc/profile so it includes the following:

export JAVA_HOME

save /etc/profile file. Then run following command to take effect.
source /etc/profile
Check to make sure JAVA_HOME is defined correctly using the command below. You should see the path to your Java JDK.
Output should be
Now need to set out new Java by default through the alternative utility. First, we will install alternative java then we will configure it make it as default java.
To install java using the alternative command:
alternatives –install /usr/bin/java java /opt/jdk1.5.0_01/bin/java 2
Now need to configure it to make it as default Java location:

alternatives -config java

Above command will given output. There we will have to select latest java location.
[root@alpeshpc opt]#alternatives –config java

There are 3 programs which provide ‘java’.

Selection Command
* 1 /usr/lib/jvm/jre-1.4.2-gcj/bin/java
2 /opt/jdk1.5.0_01/bin/java

Give there number 2, then press enter.

Thats it.