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$ sudo yum install epel-release
$ sudo yum install https://rpms.remirepo.net/enterprise/remi-release-7.rpm
$ sudo yum install --enablerepo=remi-php74 php php-mbstring

$ php -v
PHP 7.4.33 (cli) (built: Jun  5 2024 05:05:14) ( NTS )
Copyright (c) The PHP Group
Zend Engine v3.4.0, Copyright (c) Zend Technologies

　OSインストール時の標準リポジトリ「/etc/yum.repos.d/CentOS-Base.repo」は、サポートが終わりアーカイブを見るように次のように変更済。

[base]
name=CentOS-$releasever - Base
baseurl=http://vault.centos.org/7.9.2009/os/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

[updates]
name=CentOS-$releasever - Updates
baseurl=http://vault.centos.org/7.9.2009/updates/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

[extras]
name=CentOS-$releasever - Extras
baseurl=http://vault.centos.org/7.9.2009/extras/$basearch/
gpgcheck=1
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

[centosplus]
name=CentOS-$releasever - Plus
baseurl=http://vault.centos.org/7.9.2009/centosplus/$basearch/
gpgcheck=1
enabled=0
gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-CentOS-7

$ yum repolist
...
リポジトリー ID リポジトリー名                                                                 状態
base/x86_64     CentOS-7 - Base                                                                10,072
epel/x86_64     Extra Packages for Enterprise Linux 7 - x86_64                                 13,791
extras/x86_64   CentOS-7 - Extras                                                                 526
ius-vault       IUS for CentOS 7 - Vault Archive                                               11,345
remi-safe       Safe Remi's RPM repository for Enterprise Linux 7 - x86_64                      5,596
updates/x86_64  CentOS-7 - Updates                                                              6,173
repolist: 47,503

●Remiリポジトリ更新

$ sudo yum update https://rpms.remirepo.net/enterprise/remi-release-7.rpm

●インストールできるphp確認

$ yum --enablerepo=remi-safe search php

$ yum info php83

●既存 PHP 削除

$ sudo yum remove php*

●PHP 8 インストール

$ sudo yum install --enablerepo=remi-php83 php php-mbstring

▼

$ php -v
PHP 8.3.8 (cli) (built: Jun  4 2024 14:53:17) (NTS gcc x86_64)
Copyright (c) The PHP Group
Zend Engine v4.3.8, Copyright (c) Zend Technologies