yum check-update && yum update 的显示页面

当您在终端执行 `yum check-update && yum update` 命令时，会出现以下类似的显示页面：

Loaded plugins: langpacks, product-id, search-disabled-repos, subscription-manager
epel/x86_64/metalink                                    |  20 kB  00:00:00     
 * base: mirrors.neusoft.edu.cn
 * epel: ftp.cuhk.edu.hk
 * extras: mirrors.neusoft.edu.cn
 * updates: mirrors.neusoft.edu.cn
base                                                     | 3.6 kB  00:00:00     
epel                                                     | 4.7 kB  00:00:00     
extras                                                   | 3.4 kB  00:00:00     
updates                                                  | 3.4 kB  00:00:00     
(1/6): base/7/x86_64/group_gz                            | 165 kB  00:00:00     
(2/6): epel/x86_64/group_gz                              |  95 kB  00:00:00     
(3/6): extras/7/x86_64/primary_db                        | 152 kB  00:00:00     
(4/6): updates/7/x86_64/primary_db                       | 2.5 MB  00:00:01     
(5/6): base/7/x86_64/primary_db                          | 6.0 MB  00:00:02     
(6/6): epel/x86_64/primary_db                            | 6.8 MB  00:00:04     
No packages needed for security; 3 packages available
Resolving Dependencies
--> Running transaction check
---> Package openssl.x86_64 1:1.0.2k-16.el7_6.1 will be updated
---> Package openssl.x86_64 1:1.0.2k-19.el7 will be an update
---> Package openssl-devel.x86_64 1:1.0.2k-16.el7_6.1 will be updated
---> Package openssl-devel.x86_64 1:1.0.2k-19.el7 will be an update
---> Package openssl-libs.x86_64 1:1.0.2k-16.el7_6.1 will be updated
---> Package openssl-libs.x86_64 1:1.0.2k-19.el7 will be an update
--> Finished Dependency Resolution

Dependencies Resolved

================================================================================
 Package              Arch            Version                 Repository  Size
================================================================================
Updating:
 openssl              x86_64          1:1.0.2k-19.el7         base       492 k
 openssl-devel        x86_64          1:1.0.2k-19.el7         base       1.5 M
 openssl-libs         x86_64          1:1.0.2k-19.el7         base       1.2 M

Transaction Summary
================================================================================
Upgrade  3 Packages

Total download size: 3.2 M
Is this ok [y/d/N]: 

此时，`yum check-update` 命令会检查可用的软件包更新，并显示可用更新的软件包列表。`yum update` 命令则会执行软件包更新操作。在这个例子中，系统检查到有三个软件包可以更新，分别是 `openssl`、`openssl-devel` 和 `openssl-libs`。更新前，系统会提示您下载更新的软件包的大小，并询问您是否要执行更新操作。