diff --git a/tests/ci_build/CentOS-Base.repo b/tests/ci_build/CentOS-Base.repo
deleted file mode 100644
index 41fb3c1f..00000000
--- a/tests/ci_build/CentOS-Base.repo
+++ /dev/null
@@ -1,37 +0,0 @@
-[base]
-name=CentOS-$releasever - Base
-baseurl=http://vault.centos.org/centos/$releasever/os/$basearch/
-gpgcheck=1
-gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
-
-#released updates 
-[updates]
-name=CentOS-$releasever - Updates
-baseurl=http://vault.centos.org/centos/$releasever/updates/$basearch/
-gpgcheck=1
-gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
-
-#additional packages that may be useful
-[extras]
-name=CentOS-$releasever - Extras
-baseurl=http://vault.centos.org/centos/$releasever/extras/$basearch/
-gpgcheck=1
-gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
-
-#additional packages that extend functionality of existing packages
-[centosplus]
-name=CentOS-$releasever - Plus
-mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=centosplus&infra=$infra
-#baseurl=http://mirror.centos.org/centos/$releasever/centosplus/$basearch/
-gpgcheck=1
-enabled=0
-gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
-
-#contrib - packages by Centos Users
-[contrib]
-name=CentOS-$releasever - Contrib
-mirrorlist=http://mirrorlist.centos.org/?release=$releasever&arch=$basearch&repo=contrib&infra=$infra
-#baseurl=http://mirror.centos.org/centos/$releasever/contrib/$basearch/
-gpgcheck=1
-enabled=0
-gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-6
diff --git a/tests/ci_build/Dockerfile.cpu b/tests/ci_build/Dockerfile.cpu
index ad62039e..4e55d565 100644
--- a/tests/ci_build/Dockerfile.cpu
+++ b/tests/ci_build/Dockerfile.cpu
@@ -1,21 +1,12 @@
-FROM centos:6
+FROM centos:7
 LABEL maintainer "DMLC"
 
-# Environment
-ENV DEBIAN_FRONTEND noninteractive
-ENV DEVTOOLSET_URL_ROOT http://vault.centos.org/6.9/sclo/x86_64/rh/devtoolset-4/
-
-COPY CentOS-Base.repo /etc/yum.repos.d/
-
 # Install all basic requirements
 RUN \
+    yum install -y epel-release centos-release-scl && \
+    yum-config-manager --enable centos-sclo-rh-testing && \
     yum -y update && \
-    yum install -y tar unzip wget xz git yum-utils && \
-    yum install -y $DEVTOOLSET_URL_ROOT/devtoolset-4-gcc-5.3.1-6.1.el6.x86_64.rpm \
-                   $DEVTOOLSET_URL_ROOT/devtoolset-4-gcc-c++-5.3.1-6.1.el6.x86_64.rpm \
-                   $DEVTOOLSET_URL_ROOT/devtoolset-4-binutils-2.25.1-8.el6.x86_64.rpm \
-                   $DEVTOOLSET_URL_ROOT/devtoolset-4-runtime-4.1-3.sc1.el6.x86_64.rpm \
-                   $DEVTOOLSET_URL_ROOT/devtoolset-4-libstdc++-devel-5.3.1-6.1.el6.x86_64.rpm && \
+    yum install -y tar unzip wget xz git yum-utils which ninja-build devtoolset-8-gcc devtoolset-8-binutils devtoolset-8-gcc-c++ && \
     # Python
     wget https://repo.anaconda.com/miniconda/Miniconda3-latest-Linux-x86_64.sh && \
     bash Miniconda3-latest-Linux-x86_64.sh -b -p /opt/python && \
@@ -24,9 +15,9 @@ RUN \
     bash cmake-3.16.0-Linux-x86_64.sh --skip-license --prefix=/usr
 
 ENV PATH=/opt/python/bin:$PATH
-ENV CC=/opt/rh/devtoolset-4/root/usr/bin/gcc
-ENV CXX=/opt/rh/devtoolset-4/root/usr/bin/c++
-ENV CPP=/opt/rh/devtoolset-4/root/usr/bin/cpp
+ENV CC=/opt/rh/devtoolset-8/root/usr/bin/gcc
+ENV CXX=/opt/rh/devtoolset-8/root/usr/bin/c++
+ENV CPP=/opt/rh/devtoolset-8/root/usr/bin/cpp
 
 # Install Python packages
 RUN \
diff --git a/tests/ci_build/build_via_cmake.sh b/tests/ci_build/build_via_cmake.sh
index 7f66c4fd..0f5c41b7 100755
--- a/tests/ci_build/build_via_cmake.sh
+++ b/tests/ci_build/build_via_cmake.sh
@@ -5,6 +5,6 @@ set -x
 rm -rf build
 mkdir build
 cd build
-cmake .. "$@"
-make -j$(nproc)
+cmake .. -GNinja "$@"
+ninja -v
 cd ..