Installing Tomcat on Centos and Ubuntu

• Searching Java 8

# Create a Centos Machine
sudo yum update

sudo yum search jdk


sudo apt-get update
sudo apt-cache search jdk

• Repeat the same process to search for tomcat

sudo yum search tomcat

sudo apt-cache search tomcat

Findout Version of the Software to be installed

• Ubuntu: Also refer a article from here

sudo apt-cache madison <package-name>

• Exercise: Try installing older version of Jenkins on ubuntu
• Try doing the same exercise on centos

Uninstalling Software from Linux

• APT:

apt-get remove <package-name>
apt-get purge <package-name>

• YUM:

yum remove <package-name>

Important References

• Package Management

Users and Groups in Linux

• Linux is a multi-user OS
• Since multiple users are involved, managing permissions for user w.r.t any devices/folders etc.. is must to understand/

User-Creation

• To create user in linux we have useradd and adduser
• So lets try to create user1 and user2 in both centos and ubuntu.

# become root (sudo -i)
adduser user1
useradd user2

• Observe the contents of /etc/passwd

cat /etc/passwd

• Centos Users

• Ubuntu Users

• Passwd file in /etc folders shows the username, userid, groupid, home directory and default prompt

• Useradd command behavior

  • Centos:
    • Creates home directory
    • Password is not set
  • Ubuntu:
    • Doesn’t create the home directory
    • Password is not set

• adduser command behavior

  • Centos
    • Creates home directory
    • Password is not set
  • Ubuntu:
    • Creates home directory
    • Password is set when user enters password as part of the user creation

• Whenever a user is created , a group with same name as user name will also be created

• groups can be created using groupadd & deleted using group del

• To Set Password

passwd <username>

• To set basic permissions linux adopts numbering
  • Read = 4
  • Write = 2
  • Exectue = 1
• Now navigate to /home and execute

ls -la /home and check the permissions

# Sample
total 28
drwxr-xr-x  2 test    test    4096 Dec 23 02:32 test
drwxr-xr-x  5 ubuntu  ubuntu  4096 Dec 23 02:37 ubuntu
drwxr-xr-x  8 jenkins jenkins 4096 Dec 26 02:53 jenkins
drwxr-xr-x 23 root    root    4096 Dec 28 02:28 ..
drwxr-xr-x  2 user1   user1   4096 Dec 28 04:01 user1
drwxr-xr-x  2 root    root    4096 Dec 28 04:12 user2
drwxr-xr-x  7 root    root    4096 Dec 28 04:12 .

• Lets understand permissions, basic pattern is

d<User permission in rwx><group permission in rwx><others permission in rwx>

#sample
rw- => read write => 6
r-- => read 4
r-x => read execute => 5
rwx => read write execut => 7

• Changing permissions require numbering
• Whenver user is added a unique user id (uid) is created, when the user is deleted (userdel) the user name will be removed from /etc/passwd, but the uid will not be allocated to any other user
• The users created over here are local to the machine in which they are created.
• Exercise: Examine /etc/passwd file for Jenkins Master.