Mastering YUM: Build Local & Network Repositories and Install Packages on CentOS

1. Introduction to YUM

YUM is a package manager that automatically resolves dependencies when installing RPM packages from a repository.

YUM configuration files are usually located in /etc/yum.repos.d directory.

# cd /etc/yum.repos.d/
# ll
-rw-r--r--. 1 root root 1664 Sep 5 21:05 CentOS-Base.repo
-rw-r--r--. 1 root root 1309 Sep 5 21:05 CentOS-CR.repo
-rw-r--r--. 1 root root  649 Sep 5 21:05 CentOS-Debuginfo.repo
-rw-r--r--. 1 root root  314 Sep 5 21:05 CentOS-fasttrack.repo
-rw-r--r--. 1 root root  630 Sep 5 21:05 CentOS-Media.repo
-rw-r--r--. 1 root root 1331 Sep 5 21:05 CentOS-Sources.repo
-rw-r--r--. 1 root root 6639 Sep 5 21:05 CentOS-Vault.repo

2. Installing YUM

CentOS ships with YUM preinstalled. Verify the installed YUM packages:

# rpm -qa | grep yum
yum-metadata-parser-1.1.4-10.el7.x86_64
yum-plugin-fastestmirror-1.1.31-52.el7.noarch
yum-3.4.3-163.el7.centos.noarch

3. Setting up a Local CD‑ROM YUM Repository

Mount the ISO image in a virtual machine and create a mount point:

mkdir /mnt/mytest
mount /dev/sr0 /mnt/mytest   # read‑only mount
df -h                         # verify mount

Result of df -h shows the ISO is mounted at /mnt/mytest:

/dev/sr0                 4.4G  4.4G     0  100% /mnt/mytest

Make the mount permanent by adding a line to /etc/fstab:

echo "/dev/sr0 /mnt/mytest iso9660 defaults 0 0" >> /etc/fstab

Backup existing repo files and create a new local.repo:

# cd /etc/yum.repos.d/
# mkdir repo_bak
# mv *.repo repo_bak/
# touch local.repo

Example local.repo content:

[name]
name=my new repo
baseurl=file:///mnt/mytest
gpgcheck=0
enabled=1

4. Configuring a Network YUM Repository (Aliyun Mirror)

Backup current repos, then download the appropriate Aliyun repo file for the system version:

# mkdir repo_bak
# mv *.repo repo_bak/
# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

If wget is missing, install it via the local YUM repository first:

# yum -y install wget

Clean cache and rebuild the metadata:

# yum clean all
Loaded plugins: fastestmirror
Cleaning repos: base extras updates
Cleaning up everything
Cleaning up list of fastest mirrors
# yum makecache
# yum list | wc -l
10564

5. Using YUM

Basic syntax: yum [options] [command] [package…]. Common option -y answers “yes” to all prompts.

Typical commands:

# yum clean all                     # clear cache
# yum makecache                    # rebuild cache
# yum -y install httpd             # install Apache
# yum remove httpd                  # remove package
# yum update                       # update all packages
# yum list | grep httpd            # list installed/available httpd packages
# yum -y install wget && reboot    # install wget and reboot
# yum -y install net-tools         # install ifconfig
# yum -y install iputils           # install ping
# yum provides `which ifconfig`    # find which package provides a command

Common error: “Another program is locking yum; waiting for it to exit…”. Resolve by removing the lock file:

# rm -f /var/run/yum.pid

After removing the lock, YUM commands run normally.