CentOS Server Operations Practices

Compiled from the “Development Tips” series, collecting common problems and solutions in CentOS server operations.

1. Upgrading the Docker Version

Uninstall the old version of Docker

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$yum remove docker \
            docker-common \
            container-selinux \
            docker-selinux \
            docker-engine \
            docker-engine-selinux

Images, containers, data, and networks stored in /var/lib/docker/ are all preserved.

Install dependencies

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yum install -y yum-utils device-mapper-persistent-data lvm2

Install Docker

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yum-config-manager \
  --add-repo \
  https://download.docker.com/linux/centos/docker-ce.repo

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yum makecache fast

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yum install docker-ce

2. Adding a Swap Partition File

Check the current partition situation:

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free -m

Increase the swap size, around 2G:

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dd if=/dev/zero of=/var/swap bs=1024 count=2048000

Set up the swap file:

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mkswap /var/swap

Activate and enable the swap partition immediately:

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swapon /var/swap

To start it automatically at system boot, edit /etc/fstab and add a line:

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/var/swap       swap      swap     defaults   0   0

Reclaim the swap space:

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swapoff /var/swap
rm /var/swap

3. Installing minikube

Add the installation source:

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cat <<'EOF' > /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-$basearch
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOF

Start the installation:

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yum -y install kubectl
wget https://storage.googleapis.com/minikube/releases/latest/minikube-linux-amd64 -O minikube
chmod +x minikube
mv minikube  /usr/local/bin/

On Linux, minikube supports two kinds of virtual machines, VirtualBox and KVM. But if you are using a cloud server, where CPU virtualization cannot be enabled, you can use the host machine’s Docker environment:

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minikube start --vm-driver=none

See this article.

4. Installing a Specific Docker Version

Add Aliyun’s docker-ce repository:

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yum install -y yum-utils
yum-config-manager --add-repo https://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo

List the available docker-ce versions:

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yum list docker-ce --showduplicates

docker-ce.x86_64                                                                                                           17.03.3.ce-1.el7                                                                                                                   docker-ce-stable
docker-ce.x86_64                                                                                                           18.06.3.ce-3.el7                                                                                                                   docker-ce-stable
docker-ce.x86_64                                                                                                           3:18.09.9-3.el7                                                                                                                    docker-ce-stable
docker-ce.x86_64                                                                                                           3:19.03.8-3.el7                                                                                                                    docker-ce-stable

Install a specific version of docker-ce:

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yum install  -y docker-ce-19.03.8-3.el7

Start it:

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systemctl start docker
systemctl enable docker

5. Building and Installing Python 3.7

Install dependencies:

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yum install -y make build-essential libssl-dev zlib1g-dev libbz2-dev libreadline-dev libsqlite3-dev wget curl llvm libncurses5-dev libncursesw5-dev xz-utils libffi-devel

Download the source package:

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cd /usr/src
wget https://www.python.org/ftp/python/3.7.0/Python-3.7.0.tgz

Start the installation:

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tar xzf Python-3.7.0.tgz
cd Python-3.7.0
./configure --enable-optimizations
make altinstall

Check the version information:

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python3.7 -V

Install pip:

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wget https://bootstrap.pypa.io/get-pip.py -O - | python3.7
pip3 -V

6. Upgrading and Installing Git 2

Remove the old version:

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yum remove git

Install the epel-release repository:

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yum install epel-release

Install the IUS repository:

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yum install https://centos7.iuscommunity.org/ius-release.rpm

Install git2u:

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yum install git2u

7. /etc/rc.local Does Not Run Automatically at Boot

Inspecting the contents of /etc/rc.local reveals:

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# Please note that you must run 'chmod +x /etc/rc.d/rc.local' to ensure
# that this script will be executed during boot.

On CentOS 7 it is recommended to create a systemd unit for auto-start at boot.

If you need to use the old approach, you must add it to /etc/rc.d/rc.local. At the same time, run chmod +x /etc/rc.d/rc.local to grant executable permissions.

8. Checking Port Usage

Using lsof

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yum install -y lsof
lsof -i:30948

Using netstat

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yum install -y net-tools
netstat -apn | grep 30948

9. Using tcpdump to Inspect Data on a Specific Port from a Specific Source IP

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yum install -y tcpdump
tcpdump -i eth0 -nnA 'port 30948 and src host 192.168.10.3' -vv

10. Installing GLIBC 2.18

Check the installed GLIBC version:

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strings /lib64/libc.so.6 |grep GLIBC_*

GLIBC_2.2.5
GLIBC_2.2.6
GLIBC_2.3
GLIBC_2.3.2
GLIBC_2.3.3
GLIBC_2.3.4
GLIBC_2.4
GLIBC_2.5
GLIBC_2.6
GLIBC_2.7
GLIBC_2.8
GLIBC_2.9
GLIBC_2.10
GLIBC_2.11
GLIBC_2.12
GLIBC_2.13
GLIBC_2.14
GLIBC_2.15
GLIBC_2.16
GLIBC_2.17

Install GLIBC 2.18:

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wget http://ftp.gnu.org/gnu/glibc/glibc-2.XX.tar.gz
tar -xvf glibc-2.18.tar.gz
cd glibc-2.18
mkdir build && cd build
../configure --prefix=/usr
make -j4
make install