title: “Boot RHEL in Emergency Mode”
date: 2016-01-18T12:15:32
slug: boot-rhel-in-emergency-mode

In emergency mode, you are booted into the most minimal environment possible. The root file system is mounted read-only and almost nothing is set up. The main advantage of emergency mode over single-user mode is that the init files are not loaded. If init is corrupted or not working, you can still mount file systems to recover data that could be lost during a re-installation.

To change kernel parameters only during a single boot process, proceed as follows:

1.

Start the system and, on the GRUB 2 boot screen, move the cursor to the menu entry you want to edit, and press the e key for edit.

2.

Move the cursor down to find the kernel command line. The kernel command line starts with linux on 64-Bit IBM Power Series, linux16 on x86-64 BIOS-based systems, or linuxefi on UEFI systems.

3.

Move the cursor to the end of the line.

Press Ctrl+a and Ctrl+e to jump to the start and end of the line, respectively. On some systems, Home and End might also work.

4.

Edit the kernel parameters as required. For example, to run the system in emergency mode, add the emergency parameter at the end of the linux16 line:

linux16 /vmlinuz-3.10.0-0.rc4.59.el7.x86\_64 root=/dev/mapper/rhel-root ro rd.md=0 rd.dm=0 rd.lvm.lv=rhel/swap crashkernel=auto rd.luks=0 vconsole.keymap=us rd.lvm.lv=rhel/root rhgb quiet emergency

The rhgb and quiet parameters can be removed in order to enable system messages.

rhgb = redhat graphical boot – This is a GUI mode booting screen with most of the information hidden while the user sees a rotating activity icon spining and brief information as to what the computer is doing.

quiet = hides the majority of boot messages before rhgb starts. These are supposed to make the common user more comfortable. They get alarmed about seeing the kernel and initializing messages, so they hide them for their comfort.

Remount the root Filesystem RW:

mount -o remount,rw /