如何在CentOS 7上重置丟失的根密碼？

要重置CentOS 7的root密碼，可進入GRUB菜單並啟動單用戶模式。 1. 開機時反复按方向鍵中斷啟動過程以進入GRUB菜單；2. 選擇內核並按“e”編輯啟動參數；3. 在linux16行末添加rd.break，然後啟動；4. 進入initramfs shell後，重新掛載根文件系統為讀寫模式；5. 使用chroot切換至真實根環境並用passwd root修改密碼；6. 創建.autorelabel文件以確保SELinux正確重標籤；7. 輸入exit退出並重啟系統。此方法需物理或控制台訪問權限，遠程服務器需注意使用正確的控制台方式。完成後即可用新密碼登錄。

If you've lost the root password on a CentOS 7 system, don't panic — it's possible to reset it without reinstalling the OS. The process involves booting into single-user mode via the GRUB menu and changing the password from there. It's straightforward but requires physical or console access.

Accessing the GRUB Menu

CentOS 7 uses GRUB2 as its bootloader, and the first step is interrupting the boot process so you can enter the GRUB menu.

• As the system boots up, start tapping the arrow keys (usually any arrow key works) before the boot countdown finishes.
• This will stop the automatic boot and bring up the GRUB menu.
• If your system boots too fast, try holding down the arrow key during startup.

Once in the GRUB menu, select the kernel you want to boot (probably the top one), then press "e" to edit the boot configuration.

Editing the Kernel Command Line

Inside the GRUB editor, you'll see several lines of configuration. You need to modify the kernel line:

• Find the line that starts with linux16 , usually around the middle of the screen.
• At the end of that line, add rd.break — this tells the system to pause before mounting the root filesystem.
• Then press Ctrl X or F10 to boot with this modified setting.

This will drop you into a minimal shell called the "emergency mode" or initramfs shell.

Remounting Root Filesystem Read-Write

At this point, the root filesystem is mounted read-only. You need to remount it with write access:

• Run:

   mount -o remount,rw /sysroot

• Then use the chroot command to switch into the real root environment:

   chroot /sysroot

Now you're inside the system's environment and can change the root password using the standard passwd command:

 passwd root

You'll be prompted to type and confirm the new password.

After setting the password, it's important to relabel SELinux contexts, otherwise the system might get stuck on reboot:

 touch /.autorelabel

Exit the chroot environment by typing exit , then reboot the system with reboot .

Final Notes

The system should now boot normally, and you can log in with the new root password.

One thing people often forget is that if the system doesn't have a graphical interface or if you're connecting via a remote console, getting into GRUB can feel unfamiliar. Make sure you know how your system boots — for example, cloud VMs might require using a serial console instead of a regular keyboard.

Also, keep in mind that this method requires local access, which is why physical security matters for servers.

基本上就這些— once you've done it once, it becomes second nature.

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