Upgrading CentOS 6.5 to CentOS 7.2

Upgrading CentOS 6.5 to CentOS 7.2

I just recently had the job of upgrading a clients CentOS server from 6.5 to 7.2, this can be a little daunting at first but running some tests first in a VM worked well so I was OK to go. Here's how I did it.

Please note that major upgrades can cause data loss, or things can go wrong so before you start make a backup of your server. Then if things go wrong you can revert to save point.

WARNING! Do not use this method to upgrade from CentOS 6.7 or higher as several system critical packages are of a higher version number than they are in centos 7 so those do not get upgraded correctly. This renders the system broken and several system tools non-functional. You will not be able to login in or use networking.Also CentOS 6.6 fails now with the upgrade with error "Downloading failed: invalid data in .treeinfo: No section: 'checksums'" so this is also broken on CentOS 6.6 now and can ONLY be done on CentOS 6.5.

Step 1: Backup and update

In the past to update like this you had to reinstall the new CentOS then restore all your programs and data but now with CentOS 7 we can do an inlace upgrade, that being said thing can still go wrong so first make a backup of your sever once that is done we can proceed.

After you have made your backup run an update

Since the release of CentOS 6.7 and 6.8 this method is broken. If you are on CentOS 6.6 or lower then DO NOT UPDATE YOUR SYSTEM BEFORE UPGRADING this will break the upgrade process. To check your version do

CentOS 6.6 fails on upgrade to. Use this method at your own risk. The best solution is to fresh install.

cat /etc/redhat-release

If your release is CentOS 6.6 or lower then you may proceed. If you have CentOS 6.7 or 6.8 then the only way to upgrade to CentOS 7 will be to do a fresh install.

I had problems with getting Apache and MySQL and PHP to start after the upgrade so I would remove them now and reinstall them after the upgrade so in a terminal

sudo yum remove httpd httpd-tools apr apr-util mysql mysql-client compat-mysql51.x86_64 mysql-libs.x86_64 php*

Don't forget to save your configs files to restore them after the upgrade.

Step 2: Add the prerequisites

First thing to do is install the upgrade repo so as the root user you need to make a new file in '/etc/yum.repos.d/upgradetool.repo' I use nano but you can use whatever text editor you are used to:

sudo nano /etc/yum.repos.d/upgradetool.repo

Then add these line to the file

name=CentOS-$releasever - Upgrade Tool

Once done save this file. First we are going to install the pre-upgrade tool and run it to show us any potential problems, so in your terminal

Before doing this we have to openscap-1.0.8-1.0.1 thanks to Alan for this so first

sudo yum install http://dev.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm


sudo yum install preupgrade-assistant-contents redhat-upgrade-tool preupgrade-assistant

Step 3: Verifying the upgrade

Once that has installed run the pre-upgrade check to look for any potential problems, now you don't have to do this be it's better to check than not to. So in your terminal

sudo preupg

Which gives you a warning and confirmation like

Preupg tool doesn't do the actual upgrade.
Please ensure you have backed up your system and/or data in the event of a failed upgrade
 that would require a full re-install of the system from installation media.
Do you want to continue? y/n

So as we have already make a backup we would type 'y' to proceed. Next it will run some checks and give us a out like:

Result table with checks and their results for main contents:
|Bacula Backup Software                                                                    |notapplicable     |
|PostgreSQL upgrade content                                                                |notapplicable     |
|GNOME Desktop Environment underwent several design modifications in CentOS 7 release      |notapplicable     |
|KDE Desktop Environment underwent several design modifications in CentOS 7 release        |notapplicable     |
|several graphic drivers not supported in CentOS 7                                         |notapplicable     |
|several input drivers not supported in CentOS 7                                           |notapplicable     |
|Names, Options and Output Format Changes in arptables                                     |notapplicable     |
|BIND9 running in a chroot environment check.                                              |notapplicable     |
|BIND9 configuration compatibility check                                                   |notapplicable     |
|Move dhcpd/dhcprelay arguments from /etc/sysconfig/* to *.service files                   |notapplicable     |
|DNSMASQ configuration compatibility check                                                 |notapplicable     |
|Dovecot configuration compatibility check                                                 |notapplicable     |
|Net-SNMP check                                                                            |notapplicable     |
|Squid configuration compatibility check                                                   |notapplicable     |
|Added and extended options for BIND9 configuration                                        |notapplicable     |
|Added options in DNSMASQ configuration                                                    |notapplicable     |
|w3m not available in CentOS 7                                                             |notapplicable     |
|report incompatibilities between CentOS 6 and 7 in qemu-guest-agent package               |notapplicable     |
|Removed options in quota tools                                                            |notapplicable     |
|restore custom selinux configuration                                                      |notapplicable     |
|samba shared directories selinux                                                          |notapplicable     |
|CUPS Browsing/BrowsePoll configuration                                                    |notapplicable     |
|FreeRADIUS Upgrade Verification                                                           |notapplicable     |
|bind-dyndb-ldap                                                                           |notapplicable     |
|Identity Management Server compatibility check                                            |notapplicable     |
|IPA Server CA Verification                                                                |notapplicable     |
|OpenLDAP /etc/sysconfig and data compatibility                                            |notapplicable     |
|Configuration for quota_nld service                                                       |notapplicable     |
|Disk quota netlink message daemon moved into quota-nld package                            |notapplicable     |
|SSSD compatibility check                                                                  |notapplicable     |
|Clvmd and cmirrord daemon management.                                                     |notapplicable     |
|Removal of scsi-target-utils                                                              |notapplicable     |
|Configuration for warnquota tool                                                          |notapplicable     |
|Disk quota tool warnquota moved into quota-warnquota package                              |notapplicable     |
|Quorum implementation                                                                     |notapplicable     |
|fix krb5kdc config file                                                                   |notapplicable     |
|cgroups configuration compatibility check                                                 |notapplicable     |
|Ruby 2.0.0                                                                                |notapplicable     |
|SCL collections                                                                           |notapplicable     |
|NIS ypbind config files back-up                                                           |notapplicable     |
|NIS Makefile back-up                                                                      |notapplicable     |
|NIS server maps check                                                                     |notapplicable     |
|NIS server MAXUID and MAXGID limits check                                                 |notapplicable     |
|NIS server config file back-up                                                            |notapplicable     |
|several kernel networking drivers not available in CentOS 7                               |pass              |
|several kernel storage drivers not available in CentOS 7                                  |pass              |
|Reusable Configuration Files                                                              |pass              |
|NTP configuration                                                                         |pass              |
|Information on time-sync.target                                                           |pass              |
|OpenSSH sshd_config migration content                                                     |pass              |
|Luks encrypted partition                                                                  |pass              |
|Architecture Support                                                                      |pass              |
|Debuginfo packages                                                                        |pass              |
|Cluster and High Availability                                                             |pass              |
|Read Only FHS directories                                                                 |pass              |
|In-place Upgrade Requirements for the /usr/ Directory                                     |pass              |
|CA certificate bundles modified                                                           |pass              |
|Developer Tool Set packages                                                               |pass              |
|Hyper-V                                                                                   |pass              |
|Check for ethernet interface naming                                                       |pass              |
|User modification in /etc/rc.local and /etc/rc.d/rc.local                                 |pass              |
|Plugable authentication modules (PAM)                                                     |pass              |
|Python 2.7.5                                                                              |pass              |
|System kickstart                                                                          |pass              |
|Check for usage of dangerous range of UID/GIDs                                            |pass              |
|Incorrect usage of reserved UID/GIDs                                                      |pass              |
|MySQL configuration                                                                       |informational     |
|Migration of the MySQL data stack                                                         |informational     |
|Compatibility Between iptables and ip6tables                                              |informational     |
|VCS repositories                                                                          |informational     |
|Removed options in coreutils binaries                                                     |informational     |
|Removed options in gawk binaries                                                          |informational     |
|Removed options in netstat binary                                                         |informational     |
|GMP library incompatibilities                                                             |informational     |
|CVS Package Split                                                                         |informational     |
|httpd configuration compatibility check                                                   |informational     |
|File Systems, Partitions and Mounts Configuration Review                                  |informational     |
|Sonamebumped libs                                                                         |informational     |
|SonameKept Reusable Dynamic Libraries                                                     |informational     |
|Removed .so libs                                                                          |informational     |
|Foreign Perl modules                                                                      |informational     |
|YUM                                                                                       |informational     |
|Replaced rpms                                                                             |fixed             |
|package downgrades                                                                        |fixed             |
|OpenSSH sysconfig migration content                                                       |fixed             |
|State of LVM2 services.                                                                   |fixed             |
|device-mapper-multipath configuration compatibility check                                 |fixed             |
|Configuration Files to Review                                                             |needs_inspection  |
|File Lists for Manual Migration                                                           |needs_inspection  |
|Changes related to moving from MySQL to MariaDB                                           |needs_inspection  |
|Obsoleted rpms                                                                            |needs_inspection  |
|Binary rebuilds                                                                           |needs_inspection  |
|Packages not signed by CentOS                                                             |needs_action      |
|Removed rpms                                                                              |needs_action      |
|General                                                                                   |needs_action      |
|Content for enabling and disabling services based on CentOS 6 system                      |needs_action      |
Tarball with results is stored here /root/preupgrade-results/preupg_results-160124125957.tar.gz .
The latest assessment is stored in directory /root/preupgrade .
Summary information:
We found some potential in-place upgrade risks.
Read the file /root/preupgrade/result.html for more details.
Upload results to UI by command:
e.g. preupg -u -r /root/preupgrade-results/preupg_results-*.tar.gz .

Now you can read the file with the potential upgrade risks but I didn't all seemed to go well but it doesn't do any harm as you might have custom programs that will cause problems as all mine were installed from the repos I just went on to the next step which is to import the CentOS 7 repo key so in your terminal

sudo rpm --import http://mirror.centos.org/centos/RPM-GPG-KEY-CentOS-7

Step 4: Starting the upgrade

Then we have to run the upgrade tool, which doesn't do the upgrade it just downloads the updates needed to do the upgrade, that happens when we reboot the server so in your terminal

sudo /usr/bin/redhat-upgrade-tool-cli --force --network 7 --instrepo=http://mirror.centos.org/centos/7/os/x86_64

Step 5: Reboot the server

Once that has finished we are ready to do the upgrade so bit can be a bit hairy because if you are doing this on a remote server then you might not be able to see the boot process unless you have access a online console. The applying of updates will happen while the server is booting and can take 10-15 minutes so if you are doing this blind it can be a bit of a nail biting moment, but if you have already practised this like I did in a VM then you should have confidence in it working OK. That said if your machine doesn't come back online in 30 minutes then you may need to restore from your backup (you did do that backup now didn't you?). So in your terminal

sudo reboot

After waiting for about 10 minutes try logging in, if you can't try again in 10 more minutes and if you still can't in 30 minutes then you may have to restore to your save point and start again.

Step 6: Check for post upgrade problems

OK if you are still reading this you made it and have successfully logged into your server lets check our version with

sudo cat /etc/centos-release

And you should see

CentOS Linux release 7.2.1511 (Core)

Run a update

sudo yum update

if you get errors saying 'libpcre.so.0 is missing' then try reinstalling pcre.

yum reinstall pcre

and if that didn't work then try symlinking the newer pcre file to the old one with

ln -s /lib64/libpcre.so.1 /lib64/libpcre.so.0

Reinstall all Apache, MySQL and PHP. Now I didn't do this, I took the opportunity to install Nginx and MariaDB and compile my own PHP so I will do this in the next few posts.

I have to go now so I hope this has helped someone.

If you want to leave a comment please do and I will try my best at answering.

Watch on youtube: Upgrading CentOS 6.5 to 7.2

24/01/2016 14:17:00 Shaun Freeman Filed Under: Linux CentOS, Linux, Server

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