Installing Jenkins on Centos 7

I set up a Jenkins server on a brand new Centos 7 VPS. In the following the instructions for doing this in case you are looking at doing the same:

Setting up Jenkins Server

sudo yum install java-1.8.0-openjdk
sudo wget -O /etc/yum.repos.d/jenkins.repo http://pkg.jenkins-ci.org/redhat/jenkins.repo
sudo rpm --import https://jenkins-ci.org/redhat/jenkins-ci.org.key
sudo yum install jenkins

Or for stable version (link did not work for me when I tried it)

sudo wget -O /etc/yum.repos.d/jenkins.repo https://pkg.jenkins.io/redhat-stable/jenkins.repo
sudo rpm --import https://pkg.jenkins.io/redhat-stable/jenkins.io.key
yum install jenkins
  • Start Jenkins server
sudo systemctl start jenkins

You should now be able to access Jenkins at yourserver.com:8080 (if not, see troubleshooting steps at the bottom).

If you want to access your server more securely on port 80, you can do so by installing ngnix as outlined in this article in step 4: How to Install Jenkins on CentOS 7.

Connecting to a Git Repo

You will probably want to connect to a git repository next. This is also somewhat dependent on the operating system you use, so I provide the steps to do this on CentOS as well:

  • Install git
sudo yum install git
  • Generate an SSH key on the server
ssh-keygen -t rsa
  • When prompted, save the SSH key under the following path (I got this idea from reading the comments here)
/var/lib/jenkins/.ssh
  • Assure that the .ssh directory is owned by the Jenkins user:
sudo chown -R jenkins:jenkins /var/lib/jenkins/.ssh
  • Copy the public generated key to your git server (or add it in the GitHub/BitBucket web interface)
  • Assure your git server is listed in the known_hosts file. In my case, since I am using BitBucket my /var/lib/jenkins/.ssh/known_hosts file contains something like the following
bitbucket.org,104.192.143.3 ssh-rsa [...]
  • You can now create a new project and use Git as the SCM. You don’t need to provide any git credentials. Jenkins pulls these automatically form the /var/lib/jenkins/.ssh directory. There are good instructions for this available here.

Connecting to GitHub

  • In the Jenkins web interface, click on Credentials and then select the Jenkins Global credentials. Add a credential for GitHub which includes your GitHub username and password.
  • In the Jenkins web interface, click on Manage Jenkins and then on Configure System. Then scroll down to GitHub and then under GitHub servers click the Advanced Button. Then click the button Manage additional GitHub actions.

additional actions

  • In the popup select Convert login and password to token and follow the prompts. This will result in a new credential having been created. Save and reload the page.
  • Now go back to the GitHub servers section and now click to add an additional server. As credential, select the credential which you have just selected.
  • In the Jenkins web interface, click on New Item and then select GitHub organisation and connect it to your user account.

Any of your GitHub projects will be automatically added to Jenkins, if they contain a Jenkinsfile. Here is an example.

Connect with BitBucket

  • First, you will need to install the BitBucket plugin.
  • After it is installed, create a normal git project.
  • Go to the Configuration for this project and select the following option:

BitBucket trigger

  • Log into BitBucket and create a webhook in the settings for your project pointing to your Jenkins server as follows: http://youserver.com/bitbucket-hook/ (note the slash at the end)

Testing a Java Project

Chances are high you would like to run tests against a Java project, in the following, some instructions to get that working:

Troubleshooting

  • If you cannot open the Jenkins web ui, you most likely have a problem with your firewall. Temporarily disable your firewall with: `sudo systemctl stop iptables` and see if it works then.
  • If it does, you might want to check your rules in `/etc/sysconfig/iptables` and assure that port 8080 is open
  • Check the log file at:
sudo cat /var/log/jenkins/jenkins.log

 

Upgrade MySQL 5.5 to 5.6 on EC2/CentOS/RHEL

Problem

You would like to upgrade MySQL 5.5 to MySQL 5.6 on an existing server that uses the YUM software package manager.

Solution

Just enter the following few simple commands and you should be good to go. But, please, do a thorough full backup of your system before you do the upgrade just in case.

[1] Create a MySQL dump from which you will load the data into the upgraded server:

mysqldump -u root -p –add-drop-table –routines –events –all-databases –force > data-for-upgrade.sql

[2] Stop your MySQL server

sudo service mysqld stop

[3] Remove MySQL 5.5

yum remove mysql55-server mysql55-libs mysql55-devel mysql55-bench mysql55

[4] Clear the MySQL data directory

sudo rm -r /var/lib/mysql/*

[5] Install MySQL 5.6

sudo yum install mysql56 mysql56-devel mysql56-server mysql56-libs

[6] Start MySQL server

sudo service mysqld start

[7] Set the root password

/usr/libexec/mysql56/mysqladmin -u root password ‘xxx’

[8] Import your data

mysql -u root -p –force < data-for-upgrade.sql

[9] Verify all tables will work in 5.6

sudo mysql_upgrade -u root -p –force

All done!

Notes

  • Upgrade to 5.7 should work in a similar way, once 5.7 is available on your RPM repos (it isn’t by the time of the writing for the Amazon Linux Repo).

Sources

 

 

 

 

Cannot Install VirtualBox Guest Additions: Installer Hangs

Problem

For a CentOS based guest, the update of the VirtualBox Guest Additions hangs after the step: “Removing exiting VirtualBox non-DKMS kernel modules”

install

Solutions

  • Check the log file in /var/log/VBoxGuestAdditions-uninstall.log. See if there is anything obvious reported there you can fix.
  • Check if your RAM disks are valid by running the command `sudo lsinitrd`.
    • If they are not, try rebuilding broken images with `sudo dracut -f [broken-image].img [kernel version]`
  • Verify you have all dependencies installed:
    • yum install dkms
    • yum groupinstall “Development Tools”
    • yum install kernel-devel
  • Reinstall your Kernel image
  • Verify that you have the correct version of kernel-devel installed
    • yum remove kernel-devel
    • yum install kernel-devel-`uname -r`
    • Restart system!
  • Wait!
    • Let the installation run for a while, at least 15-20 min. It might do something!

newrelic service doesn’t start on CentOS: Solution Run as Root

Today one of my virtual servers suddenly showed up as offline in my New Relic console (Which is an amazing tool and free by the way).

I checked the log file /var/log/newrelic/nrsysmond.log and it had these contents:

2015-08-15 02:06:04.512 (915) error: nria_context_create(): SIGAR_OK != status; goto error; status=13

2015-08-15 02:06:04.512 (915) error: nria_context_create(): in error label

2015-08-15 02:06:04.512 (915) error: failed to create sampling context

2015-08-15 02:06:04.512 (913) info: worker process exited with 1 – NOT restarting

I found a post on the New Relic forum which provided the solution:

-> Run the newrelic service as root

This can be done by editing /etc/sysconfig/newrelic-sysmond and uncommenting the option RUNAS:

# User to run the Server Monitor as

# RUNAS=newrelic

Not a perfect solution since ideally this should run with the newrelic user but at least it got the server online on my console again.

Access Apache on VirtualBox OS from Host OS

Problem

You have a RHEL or CentOS 6 VirtualBox Virtual Machine and a Windows or other host and would like to access a web server on the VM from the Host OS.

Solution

Assure that the Apache Web Server is available and started on the guest OS:

`sudo httpd start`

Assure that firewall allows the guest OS to handle web requests.

Type ` sudo system-config-firewall` and enable the WWW service.

Configure port forwarding for the VM. Go to the VM settings in the Oracle VM VirtualBox Manager / Page ‘Network’.

Click on the button [Port Forwarding] and add an entry such as the following:

Now, on your host OS, you should be able to see the Apache Server test page when opening `http://localhost:8080` in a browser.

Troubleshooting

Since every system is configured differently there might be some problems you encounter. If you don’t see the test page, you could try the following:

  • Disable SELinux by opening the file ` /etc/selinux/config` and setting the configuration to ` SELINUX=disabled` (see a more detailed guide here)
  • This tutorial assumes that you use the default NAT network adapter for you VM. If you use a ‘host-only’ or ‘bridged’ connection, the process will be a bit different.

References

Stackoverflow – How to SSH to a VirtualBox guest externally through a host? Very helpful, also read the comments

Stackoverflow – Apache restart causes DocumentRoot must be a directory, even though it is a directory and there seem to be no privilege issues

CentOS Board – Basic firewall config (just port 80 and ssh 22)