RHEL9下dnf安装nginx-module-otel报错：找不到libcares.so.2

在RHEL9系统（UBI9容器环境）中安装nginx-module-otel时，因系统无法提供libcares.so.2()(64bit)依赖而失败，具体报错如下：

[root@6c96e0f290a0 c-ares-1.34.4]# dnf install nginx-module-otel
Updating Subscription Management repositories.
Unable to read consumer identity
Subscription Manager is operating in container mode.

This system is not registered with an entitlement server. You can use subscription-manager to register.

nginx stable repo                                                              56 kB/s |  41 kB     00:00    
Error: 
 Problem: cannot install the best candidate for the job
  - nothing provides libcares.so.2()(64bit) needed by nginx-module-otel-1:1.26.2+0.1.0-1.el9.ngx.x86_64
(try to add '--skip-broken' to skip uninstallable packages or '--nobest' to use not only best candidate packages)

已通过源码编译安装c-ares并更新了库缓存，但DNF依然无法识别该共享库。调试信息显示库文件已存在，以下是完整复现步骤及调试细节。

复现步骤 #

1. 启动UBI镜像 #

docker run -it --name ubi registry.access.redhat.com/ubi9/ubi:9.0.0-1703 /bin/bash

2. 容器内执行命令 #

# 安装开发工具
dnf install -y wget gcc gcc-c++ make

# 从源码构建c-ares
wget "https://github.com/c-ares/c-ares/releases/download/v1.34.4/c-ares-1.34.4.tar.gz"
tar xzf c-ares-1.34.4.tar.gz
cd c-ares-1.34.4
./configure --prefix=/usr --libdir=/lib64
make
make install
ldconfig

# [可选] 安装re2
dnf install -y https://dl.fedoraproject.org/pub/epel/epel-release-latest-9.noarch.rpm
dnf config-manager --set-enabled epel
/usr/bin/crb enable
dnf install -y re2-devel

# 创建nginx仓库文件
cat > /etc/yum.repos.d/nginx.repo << 'EOF'
[nginx-stable]
name=nginx stable repo
baseurl=http://nginx.org/packages/rhel/$releasever/$basearch/
gpgcheck=1
enabled=1
gpgkey=https://nginx.org/keys/nginx_signing.key
module_hotfixes=true
EOF

# 导入nginx签名密钥
rpm --import https://nginx.org/keys/nginx_signing.key

# 安装otel
dnf install nginx-module-otel

调试信息 #

[root@6c96e0f290a0 c-ares-1.34.4]# ls -l /lib64/*ares*
-rw-r--r-- 1 root root 2808910 Jan 20 08:49 /lib64/libcares.a
-rwxr-xr-x 1 root root     959 Jan 20 08:49 /lib64/libcares.la
lrwxrwxrwx 1 root root      18 Jan 20 08:49 /lib64/libcares.so -> libcares.so.2.19.3
lrwxrwxrwx 1 root root      18 Jan 20 08:49 /lib64/libcares.so.2 -> libcares.so.2.19.3
-rwxr-xr-x 1 root root 1179640 Jan 20 08:49 /lib64/libcares.so.2.19.3

[root@6c96e0f290a0 c-ares-1.34.4]# ls -l /usr/lib64/*ares*
-rw-r--r-- 1 root root 2808910 Jan 20 08:49 /usr/lib64/libcares.a
-rwxr-xr-x 1 root root     959 Jan 20 08:49 /usr/lib64/libcares.la
lrwxrwxrwx 1 root root      18 Jan 20 08:49 /usr/lib64/libcares.so -> libcares.so.2.19.3
lrwxrwxrwx 1 root root      18 Jan 20 08:49 /usr/lib64/libcares.so.2 -> libcares.so.2.19.3
-rwxr-xr-x 1 root root 1179640 Jan 20 08:49 /usr/lib64/libcares.so.2.19.3

[root@6c96e0f290a0 c-ares-1.34.4]# ldconfig -p | grep ares
        libcares.so.2 (libc6,x86-64) => /lib64/libcares.so.2
        libcares.so (libc6,x86-64) => /lib64/libcares.so

[root@6c96e0f290a0 c-ares-1.34.4]# ldconfig -v | grep ares
ldconfig: Can't stat /libx32: No such file or directory
ldconfig: Path `/usr/lib' given more than once
(from <builtin>:0 and <builtin>:0)
ldconfig: Path `/usr/lib64' given more than once
(from <builtin>:0 and <builtin>:0)
ldconfig: Can't stat /usr/libx32: No such file or directory
        libcares.so.2 -> libcares.so.2.19.3

DNF的依赖检查基于RPM包的元数据，手动编译安装的库不会被DNF识别为已提供的依赖，因此即使文件存在，依然会报错。以下是两种解决方法：

方法一：创建本地RPM包提供依赖（推荐） #

1. 安装rpm构建工具：

dnf install -y rpm-build

2. 创建spec文件~/rpmbuild/SPECS/libcares.spec：

Name:           libcares
Version:        1.34.4
Release:        1%{?dist}
Summary:        Asynchronous DNS resolver library

License:        MIT
URL:            https://c-ares.org/

%description
Asynchronous DNS resolver library.

%files
/lib64/libcares.so.2
/lib64/libcares.so.2.19.3

3. 构建RPM包：

mkdir -p ~/rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
rpmbuild -bb ~/rpmbuild/SPECS/libcares.spec

4. 安装构建好的RPM包：

rpm -ivh ~/rpmbuild/RPMS/x86_64/libcares-1.34.4-1.el9.x86_64.rpm

完成后再执行dnf install nginx-module-otel即可成功安装。

方法二：强制跳过依赖检查（仅测试环境使用） #

如果只是临时测试，可以直接用rpm强制安装，跳过依赖检查：

dnf download nginx-module-otel
rpm -ivh --nodeps nginx-module-otel-*.rpm

这种方法可能导致运行时依赖缺失，生产环境禁止使用。

内容的提问来源于stack exchange，提问作者kaushal agrawal