How to boot into rescue mode from installation DVD/ISO CentOS / RHEL 7 ?

Updated: 28 September 2026 · Applies to: AlmaLinux 9 / Rocky Linux 9

CentOS/RHEL 7 are end of life; the rescue mode of the AlmaLinux 9 / Rocky Linux 9 installation ISO works as follows. Use it when the system no longer boots from its own disk, for example after a broken kernel or boot loader update.

Boot from the installation ISO

• Ucartz VPS: in the VPS dashboard (client area › your VPS service), add the AlmaLinux 9 / Rocky Linux 9 ISO in the ISO section, set the boot order to CD Drive first, then Stop and Start the VPS and open VNC. If ISO support is not available for your VPS, ask our support team.
• Dedicated server: attach the ISO with the server's remote console, or ask our support team.

Start the rescue environment

1. In the ISO boot menu choose Troubleshooting, then Rescue a … system.
2. Choose 1) Continue so the rescue environment mounts your installed system read-write under /mnt/sysroot.
3. Press Enter for a shell, then run chroot /mnt/sysroot to work inside your installed system.

When you are done, type exit twice, remove the ISO, set the boot order back to Hard Disk and restart.

Typical repairs

• Reinstall the boot loader: dnf reinstall grub2-common grub2-tools (plus grub2-efi-x64 shim-x64 on UEFI), then grub2-mkconfig -o /boot/grub2/grub.cfg.
• Repair a file system (it must not be mounted): xfs_repair /dev/sdXN or fsck /dev/sdXN.
• Correct /etc/fstab or reset the root password with passwd.