RHEL6误使用了RHEL7的光盘源，安装了某个RPM包之后，导致glibc被升级，进而导致系统崩溃。
[root@rhel65 ~]# yum install ftp
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
This system is not registered to Red Hat Subscription Management. You can use subscription-manager to register.
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package ftp.x86_64 :0.17-.el7 will be installed
--> Processing Dependency: libc.so.(GLIBC_2.)(64bit) for package: ftp-0.17-.el7.x86_64
--> Running transaction check
---> Package glibc.x86_64 :2.12-1.132.el6 will be updated
--> Processing Dependency: glibc = 2.12-1.132.el6 for package: glibc-headers-2.12-1.132.el6.x86_64
--> Processing Dependency: glibc = 2.12-1.132.el6 for package: glibc-common-2.12-1.132.el6.x86_64
--> Processing Dependency: glibc = 2.12-1.132.el6 for package: glibc-devel-2.12-1.132.el6.x86_64
---> Package glibc.x86_64 :2.17-.el7 will be an update
--> Running transaction check
---> Package glibc-common.x86_64 :2.12-1.132.el6 will be updated
---> Package glibc-common.x86_64 :2.17-.el7 will be an update
--> Processing Dependency: /usr/bin/bash for package: glibc-common-2.17-.el7.x86_64
---> Package glibc-devel.x86_64 :2.12-1.132.el6 will be updated
---> Package glibc-devel.x86_64 :2.17-.el7 will be an update
---> Package glibc-headers.x86_64 :2.12-1.132.el6 will be updated
---> Package glibc-headers.x86_64 :2.17-.el7 will be an update
--> Running transaction check
---> Package bash.x86_64 :4.1.-.el6_4 will be updated
---> Package bash.x86_64 :4.2.-.el7_2 will be an update
--> Processing Conflict: bash-4.2.-.el7_2.x86_64 conflicts filesystem <
--> Restarting Dependency Resolution with new changes.
--> Running transaction check
---> Package filesystem.x86_64 :2.4.-.el6 will be updated
---> Package filesystem.x86_64 :3.2-.el7 will be an update
--> Finished Dependency Resolution Dependencies Resolved ===========================================================================================================
Package Arch Version Repository Size
===========================================================================================================
Installing:
ftp x86_64 0.17-.el7 rhel73-iso k
Updating:
filesystem x86_64 3.2-.el7 rhel73-iso 1.0 M
Updating for dependencies:
bash x86_64 4.2.-.el7_2 rhel73-iso 1.0 M
glibc x86_64 2.17-.el7 rhel73-iso 3.6 M
glibc-common x86_64 2.17-.el7 rhel73-iso M
glibc-devel x86_64 2.17-.el7 rhel73-iso 1.1 M
glibc-headers x86_64 2.17-.el7 rhel73-iso k Transaction Summary
===========================================================================================================
Install Package(s)
Upgrade Package(s) Total download size: M
Is this ok [y/N]: y
Downloading Packages:
-----------------------------------------------------------------------------------------------------------
Total MB/s | MB :
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Updating : glibc-2.17-.el7.x86_64 /
Updating : bash-4.2.-.el7_2.x86_64 /
Updating : glibc-common-2.17-.el7.x86_64 /
Updating : glibc-headers-2.17-.el7.x86_64 /
Updating : glibc-devel-2.17-.el7.x86_64 /
Updating : filesystem-3.2-.el7.x86_64 /
Error unpacking rpm package filesystem-3.2-.el7.x86_64
error: unpacking of archive failed on file /bin: cpio: rename
Installing : ftp-0.17-.el7.x86_64 /
Cleanup : glibc-devel-2.12-1.132.el6.x86_64 /
Cleanup : glibc-headers-2.12-1.132.el6.x86_64 /
Cleanup : bash-4.1.-.el6_4.x86_64 /
Non-fatal POSTUN scriptlet failure in rpm package bash
Cleanup : glibc-common-2.12-1.132.el6.x86_64 /
warning: %postun(bash-4.1.-.el6_4.x86_64) scriptlet failed, exit status
Cleanup : glibc-2.12-1.132.el6.x86_64 /
warning: /etc/localtime saved as /etc/localtime.rpmsave
Non-fatal <unknown> scriptlet failure in rpm package glibc
rhel65-iso/productid | 1.7 kB : ...
rhel73-iso/productid | 1.6 kB : ...
Verifying : glibc-devel-2.17-.el7.x86_64 /
Verifying : bash-4.2.-.el7_2.x86_64 /
Verifying : glibc-2.17-.el7.x86_64 /
Verifying : glibc-common-2.17-.el7.x86_64 /
Verifying : ftp-0.17-.el7.x86_64 /
Verifying : glibc-headers-2.17-.el7.x86_64 /
Verifying : glibc-2.12-1.132.el6.x86_64 /
Verifying : glibc-devel-2.12-1.132.el6.x86_64 /
Verifying : bash-4.1.-.el6_4.x86_64 /
filesystem-2.4.-.el6.x86_64 was supposed to be removed but is not!
Verifying : filesystem-2.4.-.el6.x86_64 /
Verifying : glibc-common-2.12-1.132.el6.x86_64 /
Verifying : glibc-headers-2.12-1.132.el6.x86_64 /
Verifying : filesystem-3.2-.el7.x86_64 / Installed:
ftp.x86_64 :0.17-.el7 Dependency Updated:
bash.x86_64 :4.2.-.el7_2 glibc.x86_64 :2.17-.el7 glibc-common.x86_64 :2.17-.el7
glibc-devel.x86_64 :2.17-.el7 glibc-headers.x86_64 :2.17-.el7 Failed:
filesystem.x86_64 :2.4.-.el6 filesystem.x86_64 :3.2-.el7 Complete!
查看yum install升级记录日志
此时系统已经不能正常执行reboot命令重启了，只能强制按电源重启机器。重启之后，原系统已经崩溃，进不去系统了，停在下面的界面：
然后使用RHEL6的光盘引导机器，选择rescue，进入到shell之后提示无法chroot到/mnt/sysimage，无解。
然后重启，用RHEL6安装光盘引导机器，选择Install or Update系统，进入图形后选择update已有系统，失败，如下图。
然后按ctrl+alt+F2切换到第2个console，发现原系统已经被自动挂载到/mnt/sysimage目录，尝试chroot到/mnt/sysimage，由于bash被上面依赖更新了，所以会提示找不到/bin/sh，手动把/mnt/sysimage/usr/bin/sh 拷到 /mnt/sysimage/bin/sh，再次chroot成功。
手工挂载RHEL6的ISO到/mnt/rhel65并cd到Packages目录，强制将上面更新过的几个包更新回到RHEL6的版本：
# rpm --force --nodeps -Uvh [RPM包名]
分别把bash/glibc/glibc-common/glibc-devel/glibc-headers这几个包装回去。
重启系统，发现已经可以正常进入到原系统了，最后使用yum remove把最开始安装的RHEL7的包给remove掉，问题全部解决。