Update centos 7 on hardware-and-software-requirements.md (#20020)

Co-authored-by: Daniël van Eeden <[email protected]>
Co-authored-by: Aolin <[email protected]>

Author: 3 people

hardware-and-software-requirements.md

@@ -62,8 +62,10 @@ In v8.5 LTS, TiDB ensures multi-level quality standards for various combinations
 
     > **Warning:**
     >
-    > - According to [CentOS Linux EOL](https://blog.centos.org/2023/04/end-dates-are-coming-for-centos-stream-8-and-centos-linux-7/), the upstream support for CentOS Linux 7 ends on June 30, 2024. TiDB ends the support for CentOS 7 starting from the 8.4 DMR version. It is recommended to use Rocky Linux 9.1 or a later version. Upgrading a TiDB cluster on CentOS 7 to v8.4.0 or later will cause the cluster to become unavailable. Before upgrading TiDB, make sure to check your operating system version.
-    > - According to [Red Hat Enterprise Linux Life Cycle](https://access.redhat.com/support/policy/updates/errata/#Life_Cycle_Dates), the maintenance support for Red Hat Enterprise Linux 7 ends on June 30, 2024. TiDB ends the support for Red Hat Enterprise Linux 7 starting from the 8.4 DMR version. It is recommended to use Rocky Linux 9.1 or a later version. Upgrading a TiDB cluster on Red Hat Enterprise Linux 7 to v8.4.0 or later will cause the cluster to become unavailable. Before upgrading TiDB, make sure to check your operating system version.
+    > - According to [CentOS Linux EOL](https://blog.centos.org/2023/04/end-dates-are-coming-for-centos-stream-8-and-centos-linux-7/), the upstream support for CentOS Linux 7 ended on June 30, 2024.
+    >     - Before upgrading TiDB, make sure to check your operating system version. TiDB v8.4.0 DMR and v8.5.0 removed the support of glibc 2.17, and dropped support and testing with CentOS Linux 7. It is recommended to use Rocky Linux 9.1 or a later version. Upgrading a TiDB cluster on CentOS 7 to v8.4.0 or v8.5.0 will cause the risk of cluster unavailability.
+    >     - Starting from v8.5.1, to assist users still using CentOS Linux 7, TiDB resumes the support of glibc 2.17, resumes testing of CentOS Linux 7, and is now compatible with CentOS Linux 7. However, due to the EOL status of CentOS Linux, it is strongly recommended that you review the [official announcements and security guidance](https://www.redhat.com/en/blog/centos-linux-has-reached-its-end-life-eol) for CentOS Linux 7 and migrate to an operating system supported by TiDB for production use, such as Rocky Linux 9.1 or later.
+    > - According to [Red Hat Enterprise Linux Life Cycle](https://access.redhat.com/support/policy/updates/errata/#Life_Cycle_Dates), the maintenance support for Red Hat Enterprise Linux 7 ended on June 30, 2024. TiDB ends the support for Red Hat Enterprise Linux 7 starting from the 8.4 DMR version. It is recommended to use Rocky Linux 9.1 or a later version. Upgrading a TiDB cluster on Red Hat Enterprise Linux 7 to v8.4.0 or later will cause the cluster to become unavailable. Before upgrading TiDB, make sure to check your operating system version.
 
 + For the following combinations of operating systems and CPU architectures, you can compile, build, and deploy TiDB. In addition, you can also use the basic features of OLTP, OLAP, and the data tools. However, TiDB **does not guarantee enterprise-level production quality**:
 
@@ -120,8 +122,6 @@ In v8.5 LTS, TiDB ensures multi-level quality standards for various combinations
 
 + Other operating system versions not mentioned above might work but are not officially supported.
 
-+ Starting from v8.4.0, TiDB requires glibc 2.28. If your glibc version does not meet this requirement, it is recommended to use an operating system listed in the preceding table or upgrade the operating system to a version that supports glibc 2.28.
-
 ### Libraries required for compiling and running TiDB
 
 |  Libraries required for compiling and running TiDB |  Version   |

upgrade-tidb-using-tiup.md

@@ -9,7 +9,7 @@ This document applies to upgrading to TiDB v8.5.x from the following versions: v
 
 > **Warning:**
 >
-> 1. Starting from v8.4.0, TiDB no longer supports CentOS 7 and Red Hat Enterprise Linux 7. It is recommended to use Rocky Linux 9.1 or later. Upgrading a TiDB cluster running on CentOS 7 or Red Hat Enterprise Linux 7 to v8.4.0 or later will cause the cluster to become unavailable. Before upgrading TiDB, ensure that your operating system version meets the [OS and platform requirements](/hardware-and-software-requirements.md#os-and-platform-requirements).
+> 1. Before upgrading TiDB, ensure that your operating system version meets the [OS and platform requirements](/hardware-and-software-requirements.md#os-and-platform-requirements). If you plan to upgrade your cluster running on CentOS Linux 7 to v8.5, ensure you use TiDB v8.5.1 or a later version to avoid the risk of cluster unavailability. For more information, see [TiDB v8.5.1 Release Notes](/releases/release-8.5.1.md).
 > 2. You cannot upgrade TiFlash online from versions earlier than 5.3 to 5.3 or later. Instead, you must first stop all the TiFlash instances of the early version, and then upgrade the cluster offline. If other components (such as TiDB and TiKV) do not support an online upgrade, follow the instructions in warnings in [Online upgrade](#online-upgrade).
 > 3. **DO NOT** run DDL statements during the upgrade process. Otherwise, the issue of undefined behavior might occur.
 > 4. **DO NOT** upgrade a TiDB cluster when a DDL statement is being executed in the cluster (usually for the time-consuming DDL statements such as `ADD INDEX` and the column type changes). Before the upgrade, it is recommended to use the [`ADMIN SHOW DDL`](/sql-statements/sql-statement-admin-show-ddl.md) command to check whether the TiDB cluster has an ongoing DDL job. If the cluster has a DDL job, to upgrade the cluster, wait until the DDL execution is finished or use the [`ADMIN CANCEL DDL`](/sql-statements/sql-statement-admin-cancel-ddl.md) command to cancel the DDL job before you upgrade the cluster.