CentOS身为企业级Linux发行版, 它的版本演进对服务器选型以及运维策略有着直接影响, 从CentOS 6到CentOS Stream, 各个版本在生命周期方面、软件包管理方面以及内核特性方面都有非常明显的差异, 可掌握系统信息查询技能却是日常管理的基础；本文依据实际运维经验来梳理版本特性和关键查询命令。
版本迭代的核心变化
CentOS 8是从CentOS 6升级跨度最大的版本, CentOS 6是基于RHEL 6而成, 且采用ext4文件系统以及SysVinit初始化系统, 还支持Xen虚拟化, 它在2020年结束了生命周期, 当前仅有少量遗留系统仍在运行。CentOS 7全面转换到了systemd和XFS文件系统 , 默认情形下用firewalld替换了iptables, 对Docker容器的支持更为完善, 成为过去五年里最主流的服务器版本。CentOS 8时, dnf替代yum成了包管理器, 模块化流也就是AppStream, 它能让不同版本的软件同时进行安装, 然而在2021年底就早早地停止维护了, 这让众多运维人员毫无防备, 十分突然。
CentOS Stream的定位有着更为特别之处, 它并非是对RHEL的全然克隆, 而是属于滚动更新的那种“上游预览版”, 处于Fedora和RHEL两者之间, 这就表明你没法获取到长期稳定的API和ABI, 不过能够提前去体验新特性, 适宜用于开发测试环境而非生产服务器, 要是你需要长期的稳定, 倒不如直接去考虑Rocky Linux或者AlmaLinux这类替代品。
系统信息查询的关键命令
用lscpu查看CPU信息最为直接, 它能够让你知悉架构、核心数、线程数以及虚拟化支持情况。在内存方面, free -h用来展示总量与使用量, 然而更细致的缓存以及缓冲区信息得查看cat /proc/meminfo。借助lsblk可对磁盘分区进行查看, 从而了解设备树结构, df -hT则会告知你挂载点、文件系统类型以及剩余空间状况。将这些命令组合起来, 在一两分钟之内便能够摸清楚服务器硬件的底细。
关于内核与发行版信息, 存在专门的工具, uname -a会输出内核版本、主机名以及硬件架构, cat /etc/os-release或者hostnamectl会显示CentOS的具体版本号, 要是你想知道某个软件包版本, 在CentOS 7上rpm -qa | grep包名仍然可以使用, 在CentOS 8及以上, 则需使用dnf list installed。在网络配置相关领域, 通过ip addr去查看IP地址, 借助ss -tlnp来查看监听端口, 这二者取代了以往老旧的ifconfig以及netstat。
运行时长以及系统启动的时间, 借助应用uptime便可查看得到, 并且还会附带负载均衡方面的数据。要是对系统之中存有疑问觉得拥有异常进程情况, top 或者 htop 则能够实时监控 CPU方面以及内存的情况, 知晓哪组进程占用情况是最高的。日志查询这一行为离开了journalctl那是不行的, 可以使用journalctl -u服务名来精确地过滤某一个服务之中的日志，这种方式比去翻/var/log/messages要高效出许多。
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