Upgrading CentOS 6 to CentOS 7

PRE TASKS

There are some tasks you can do to prevent from unwanted results. Like:

• Disable selinux
• Remove unnecessary repositories
• Take a recent backup!

CENTOS UPGRADE REPOSITORY

Create a new centos repository:

cat > /etc/yum.repos.d/centos-upgrade.repo <<EOF
[centos-upgrade]
name=centos-upgrade
baseurl=https://buildlogs.centos.org/centos/6/upg/x86_64/
enabled=1
gpgcheck=0
EOF

INSTALL PRE-UPGRADE TOOL

First install the openscap version from dev.centos.org:

# yum -y install https://buildlogs.centos.org/centos/6/upg/x86_64/Packages/openscap-1.0.8-1.0.1.el6.centos.x86_64.rpm

then install the redhat upgrade tool:

# yum -y install redhat-upgrade-tool preupgrade-assistant-*

IMPORT CENTOS 7 PGP KEY

# rpm --import http://mirror.centos.org/centos/7/os/x86_64/RPM-GPG-KEY-CentOS-7

NOTE:

to bypass errors like:

Downloading failed: invalid data in .treeinfo: No section: ‘checksums’

append CentOS Mirror under mirrorlist:

mkdir -pv /var/tmp/system-upgrade/base/ /var/tmp/system-upgrade/extras/ /var/tmp/system-upgrade/updates/

echo http://mirror.centos.org/centos/7/os/x86_64/ >> /var/tmp/system-upgrade/base/mirrorlist.txt
echo http://mirror.centos.org/centos/7/extras/x86_64/ >> /var/tmp/system-upgrade/extras/mirrorlist.txt
echo http://mirror.centos.org/centos/7/updates/x86_64/ >> /var/tmp/system-upgrade/updates/mirrorlist.txt

PRE-UPGRADE

preupg is actually a python script!

# yes | preupg -v
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
Gathering logs used by preupgrade assistant:
All installed packages : 01/11 ...finished (time 00:00s)
All changed files : 02/11 ...finished (time 00:18s)
Changed config files : 03/11 ...finished (time 00:00s)
All users : 04/11 ...finished (time 00:00s)
All groups : 05/11 ...finished (time 00:00s)
Service statuses : 06/11 ...finished (time 00:00s)
All installed files : 07/11 ...finished (time 00:01s)
All local files : 08/11 ...finished (time 00:01s)
All executable files : 09/11 ...finished (time 00:01s)
RedHat signed packages : 10/11 ...finished (time 00:00s)
CentOS signed packages : 11/11 ...finished (time 00:00s)
Assessment of the system, running checks / SCE scripts:
001/096 ...done (Configuration Files to Review)
002/096 ...done (File Lists for Manual Migration)
003/096 ...done (Bacula Backup Software)
...
./result.html
/bin/tar: .: file changed as we read it
Tarball with results is stored here /root/preupgrade-results/preupg_results-180508202952.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 http://127.0.0.1:8099/submit/ -r /root/preupgrade-results/preupg_results-*.tar.gz .
this must finish without any errors.

CENTOS UPGRADE TOOL

We need to find out what are the possible problems when upgrade:

# centos-upgrade-tool-cli --network=7 --instrepo=http://vault.centos.org/7.0.1406/os/x86_64/

Then by force we can upgrade to it’s latest version:

# centos-upgrade-tool-cli --force --network=7 --instrepo=http://vault.centos.org/7.0.1406/os/x86_64/ --cleanup-post

Output:

setting up repos...
base | 3.6 kB 00:00
base/primary_db | 4.9 MB 00:04
centos-upgrade | 1.9 kB 00:00
centos-upgrade/primary_db | 14 kB 00:00
cmdline-instrepo | 3.6 kB 00:00
cmdline-instrepo/primary_db | 4.9 MB 00:03
epel/metalink | 14 kB 00:00
epel | 4.7 kB 00:00
epel | 4.7 kB 00:00
epel/primary_db | 6.0 MB 00:04
extras | 3.6 kB 00:00
extras/primary_db | 4.9 MB 00:04
mariadb | 2.9 kB 00:00
mariadb/primary_db | 33 kB 00:00
remi-php56 | 2.9 kB 00:00
remi-php56/primary_db | 229 kB 00:00
remi-safe | 2.9 kB 00:00
remi-safe/primary_db | 950 kB 00:00
updates | 3.6 kB 00:00
updates/primary_db | 4.9 MB 00:04
.treeinfo | 1.1 kB 00:00
getting boot images...
vmlinuz-redhat-upgrade-tool | 4.7 MB 00:03
initramfs-redhat-upgrade-tool.img | 32 MB 00:24
setting up update...
finding updates 100% [=========================================================]
(1/323): MariaDB-10.2.14-centos6-x86_64-client.rpm | 48 MB 00:38
(2/323): MariaDB-10.2.14-centos6-x86_64-common.rpm | 154 kB 00:00
(3/323): MariaDB-10.2.14-centos6-x86_64-compat.rpm | 4.0 MB 00:03
(4/323): MariaDB-10.2.14-centos6-x86_64-server.rpm | 109 MB 01:26
(5/323): acl-2.2.51-12.el7.x86_64.rpm | 81 kB 00:00
(6/323): apr-1.4.8-3.el7.x86_64.rpm | 103 kB 00:00
(7/323): apr-util-1.5.2-6.el7.x86_64.rpm | 92 kB 00:00
(8/323): apr-util-ldap-1.5.2-6.el7.x86_64.rpm | 19 kB 00:00
(9/323): attr-2.4.46-12.el7.x86_64.rpm | 66 kB 00:00
...
(320/323): yum-plugin-fastestmirror-1.1.31-24.el7.noarch.rpm | 28 kB 00:00
(321/323): yum-utils-1.1.31-24.el7.noarch.rpm | 111 kB 00:00
(322/323): zlib-1.2.7-13.el7.x86_64.rpm | 89 kB 00:00
(323/323): zlib-devel-1.2.7-13.el7.x86_64.rpm | 49 kB 00:00
testing upgrade transaction
rpm transaction 100% [=========================================================]
rpm install 100% [=============================================================]
setting up system for upgrade
Finished. Reboot to start upgrade.

REBOOT

The upgrade procedure, will download all rpm packages to a directory and create a new grub entry. Then on reboot the system will try to upgrade the distribution release to it’s latest version.

# reboot

When this error appears :

/bin/grep: error while loading shared libraries: libpcre.so.0: cannot open shared object file: No such file or directory

Run the following command:

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

Disclaimer : Create a recent backup of the system. This is an unofficial , unsupported procedure !

After reboot you may need to upgrade bootloader into grub2, you can follow this link

source: http://fsfe.soup.io/post/651104763/Evaggelos-Balaskas-System-Engineer-CentOS-Dist-Upgrade