What is rescue mode in linux

What is rescue mode in linux

Rescue mode is a term used to describe a method of booting a small Linux environment completely from diskettes.

What follows in this section may help you recover from a problem at some point. A copy of these instructions is also available as rescue.txt on your Red Hat Linux 6.0 CD-ROM.

As the name implies, rescue mode is there to rescue you from something. In normal operation, your Red Hat Linux system uses files located on your system’s hard drive to do everything — run programs, store your files, and more.

However, there may be times when you are unable to get Linux running completely enough to access its files on your system’s hard drive. By using rescue mode, it’s possible to access the files stored on your system’s hard drive, even if you can’t actually run Linux from that hard drive.

Normally, you’ll need to get into rescue mode for one of two reasons:

You are unable to boot Linux, and you’d like to fix it.

You are having hardware or software problems, and you want to get a few important files off your system’s hard drive.

Let’s take a closer look at each these scenarios.

Unable to boot Linux

Hardware/software problems

What do you need to get into rescue mode?

To get into rescue mode, you’ll need a rescue disk set. These are two diskettes that contain the files necessary to boot into rescue mode.

If you elected to make a boot diskette while you were installing Red Hat Linux, you’re halfway there! The first diskette in a rescue disk set is this boot diskette.

Now on to the second diskette.

The second diskette is called the rescue diskette. It is produced by writing an image file onto a diskette. The image file is called rescue.img, and is located in the images directory on the first Red Hat Linux CD-ROM.

To gain access to this file, you’ll first need to mount your Red Hat Linux CD-ROM.

Start by inserting the CD-ROM in your system’s CD-ROM drive. You’ll need to do this while logged in as root.

Type the following command:

You may get an error message from the first command saying that the file exists. That’s fine; we just want to make sure that there is a /mnt/cdrom directory on your system. The second command should issue an informational message that /dev/cdrom is being mounted read-only.

Please Note: Some systems may not recognize /dev/cdrom. If this is your case, you’ll have to replace /dev/cdrom in the command with the appropriate device name for your CD-ROM.

Next, issue the following command (again, while logged in as root):

to list the contents of the images directory.

You should see a file named rescue.img. This is the rescue diskette image file. Next, put a diskette in your first diskette drive, and enter the following command:

Your system’s diskette drive should start writing to the diskette. After a minute or so, the dd command will complete, and you’ll get your shell prompt back.

Wait for your diskette drive’s access light to go out, and that’s it!

You now have a rescue disk set. Label this diskette something like «Red Hat Linux 6.0 rescue diskette» and store it someplace safe.

Let’s hope you never have to use it.

If you should ever need to use rescue mode, here’s how.

Boot your system with the boot diskette in the first diskette drive. At the LILO Boot: prompt, enter the word rescue. You will see the usual kernel messages as the Linux kernel starts up.

Eventually, it will ask you to insert the next diskette, and press [Enter]. Remove the boot diskette, insert the rescue diskette, and press [Enter].

The rescue diskette will be read into memory. After a minute or so, you should see the shell prompt. That’s it — you’re in rescue mode!

When it comes to rescue mode, that’s a bit like asking, «how long is a piece of string?» What you require depends a great deal on what your system’s problem is, your level of Linux expertise, and several variables we haven’t even thought of yet. So we can’t give you explicit instructions.

But we can tell you what programs you have access to while in rescue mode.

You’re likely to be unfamiliar with most, if not all of these commands. However, the commands do have man pages. Once you begin to feel more comfortable with commands, you should consider familiarizing yourself them through the man pages. (You may not have that luxury if you have to use these commands. )

You’ve worked with some pretty useful commands for your Red Hat Linux system so far. You may not have known much about where those files were in the directory, however.

For more information about the Linux filesystem, including navigation and working with other useful commands to help you understand your system, turn to the next chapter.

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How to Boot into Rescue Mode Or Emergency Mode In Ubuntu 20.04 / 18.04

It’s not uncommon for users to forget their login passwords or have their system suffer a corrupt filesystem. When that happens, the recommended solution is to boot into rescue or emergency mode and apply the required fixes.

The rescue mode is also referred to as the single-user mode. As the name suggests, the rescue mode is used when you want to salvage your system from a system failure, for example, boot failure or reset a password. In rescue mode, all the local filesystems are mounted. However, only salient services are started. Normal services such as network services will not be started.

Emergency mode provides a minimal bootable environment and enables you to repair your Linux system even when rescue mode is not available. In emergency mode, only the root file system is mounted, and in read-only mode. Just as with rescue mode, only the essential services are activated in emergency mode.

In this guide, you will learn how to boot into rescue mode or emergency mode in Ubuntu 20.04 / 18.04.

On this page

Booting Ubuntu 20.04 in Rescue Mode

To get started, boot, or reboot your system. You will get the grub menu with options listed as shown. If you are running Ubuntu as a VM in VirtualBox, press the ESC button.

By default, the first option is selected. With the first option selected, press the ‘e’ key on the keyboard to access the grub parameters.

Ubuntu Grub Menu

Scroll and locate the line that starts with ‘linux’ . Go to the very end of the line by pressing ctrl + e and delete the string “$vt_handoff” .

Edit Grub Parameters

Next, append ‘systemd.unit=rescue.target’ at the end of the line.

Enable Rescue Mode in Ubuntu

To boot the system into rescue mode, press ctrl + x . Proceed and press ENTER on your keyboard to gain access to the rescue mode. From there you can perform operations such as changing a user’s password. In the example below, I have managed to reset my password.

In rescue mode, all filesystems are mounted in read & write mode and you can run almost any commands just as you would in a normal session. Once you are done, reboot the system to save the changes using the command:

Reset Password in Ubuntu

Booting Ubuntu 20.04 in Emergency Mode

As we mentioned earlier, in emergency mode, all files are mounted in read-only mode. The emergency mode comes in handy especially when it’s not possible to boot into rescue mode due to file system corruption.

To boot into emergency mode, reboot or boot your system. On the grub menu, ensure that the first option is highlighted and press the ‘e’ key on the keyboard to access the grub parameters.

Ubuntu Grub Menu

Once again, navigate to the end of the line by pressing ctrl + e and delete the string “$vt_handoff” .

Edit Grub Parameters

Next, append the ‘systemd.unit=emergency.target’ string at the end of the line.

Enable Emergency Mode in Ubuntu

Thereafter, press ctrl + x to reboot into emergency mode. Hit ENTER to access the root filesystem. From here you can view various files on your Linux system. In this example, we are viewing the contents of the /etc/fstab to see the mount points that are defined.

Emergency Mode in Ubuntu

To make any changes to the system, you need to mount it in read and write mode as shown.

From here, you can perform any troubleshooting tasks such as changing the root password as shown. Once you are done, reboot for the changes to come into effect.

This draws the curtain on this article. Hopefully, you can now access both the rescue and emergency mode and fix system issues in the Ubuntu system.

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What is rescue mode in linux

When things go wrong, there are ways to fix problems. However, these methods require that you understand the system well. This chapter describes how to boot into rescue mode, single-user mode, and emergency mode, where you can use your own knowledge to repair the system.

You might need to boot into one of these recovery modes for any of the following reasons:

You are unable to boot normally into Red Hat Linux runlevel(3 or 5).

You are having hardware or software problems, and you want to get a few important files off of your system’s hard drive.

You forgot the root password.

Unable to Boot into Red Hat Linux

This problem is often caused by the installation of another operating system after you have installed Red Hat Linux. Some other operating systems assume that you have no other operating systems on your computer. They overwrite the Master Boot Record (MBR) that originally contained the GRUB or LILO boot loader. If the boot loader is overwritten in this manner, you will not be able to boot Red Hat Linux unless you can get into rescue mode and reconfigure the boot loader.

Another common problem occurs when using a partitioning tool to resize a partition or create a new partition from free space after installation, and it changes the order of your partitions. If the partition number of your / partition changes, the boot loader might not be able to find it to mount the partition. To fix this problem, boot in rescue mode and modify /boot/grub/grub.conf if you are using GRUB or /etc/lilo.conf if you are using LILO. You must also run the /sbin/lilo command anytime you modify the LILO configuration file.

Hardware/Software Problems

This category includes a wide variety of different situations. Two examples include failing hard drives and specifying an invalid root device or kernel in the boot loader configuration file. If either of these occur, you might not be able to reboot into Red Hat Linux. However, if you boot into one of the system recovery modes, you might be able to resolve the problem or at least get copies of your most important files.

Root Password

What can you do if you forget your root password? To reset it to a different password, boot into rescue mode or single-user mode and use the passwd command to reset the root password.

Booting into Rescue Mode

Rescue mode provides the ability to boot a small Red Hat Linux environment entirely from a diskette, CD-ROM, or some other boot method instead of the system’s hard drive.

As the name implies, rescue mode is provided to rescue you from something. During normal operation, your Red Hat Linux system uses files located on your system’s hard drive to do everything — run programs, store your files, and more.

However, there may be times when you are unable to get Red Hat Linux running completely enough to access files on your system’s hard drive. Using rescue mode, you can access the files stored on your system’s hard drive, even if you cannot actually run Red Hat Linux from that hard drive.

To boot into rescue mode, be able to boot the system using one of the following methods:

By booting the system from an installation boot diskette made from the bootdisk.img image.

By booting the system from an installation boot CD-ROM.

By booting the system from the Red Hat Linux CD-ROM #1.

Once you have booted using one of the described methods, enter the following command at the installation boot prompt:

You are prompted to select where a valid rescue image is located. Select from «Local CD-ROM», «Hard Drive», «NFS image», «FTP», or «HTTP».

The location selected must contain a valid installation tree, and the installation tree must be for the same version of Red Hat Linux as the Red Hat Linux CD-ROM #1 from which you booted. If you used a boot CD-ROM or diskette to start rescue mode, the installation tree must be from the same tree from which the media was created.

If you select a rescue image that does not require a network connect, you are asked whether or not you want to establish a network connection. A network connection is useful if you need to backup files to a different computer or install some RPM packages from a shared network location, for example.

You will also see the following message:

If you select «Continue», it will attempt to mount your file system under the directory /mnt/sysimage. If it fails to mount a partition, it will notify you. If you select «Read-Only», it will attempt to mount your file system under the directory /mnt/sysimage, but in read-only mode. If you select «Skip», your file system will not be mounted. Choose «Skip» if you think your file system is corrupted.

Once you have your system in rescue mode, a prompt appears on VC (virtual console) 1 and VC 2 (use the [Ctrl] — [Alt] — [F1] key combination to access VC 1 and [Ctrl] — [Alt] — [F2] to access VC 2):

If you selected «Continue» to mount your partitions automatically and they were mounted successfully, you are in single-user mode.

Even if your file system is mounted, the default root partition while in rescue mode is a temporary root partition, not the root partition of the file system used during normal user mode runlevel(3 or 5). If you selected to mount your file system and it mounted successfully, you can change the root partition of the rescue mode environment to the root partition of your file system by executing the following command:

This is useful if you need to run commands such as rpm that require your root partition to be mounted as /. To exit the chroot environment, type exit, and you will return to the prompt.

If you selected «Skip», you can still try to mount a partition manually inside rescue mode by creating a directory such as /foo , and typing the following command:

In the above command, /foo is a directory that you have created and /dev/hda5 is the partition you want to mount. If the partition is of type ext2, replace ext3 with ext2.

If you do not know the names of your partitions, use the following command to list them:

From the prompt, you can run many useful commands such as

• list-harddrives to list the hard drives in the system
• ssh,scp, and ping if the network is started
• dump and restore for users with tape drives
• parted and fdisk for managing partitions
• rpm for installing or upgrading software
• joe for editing configuration files (If you try to start other popular editors such as emacs, pico, or vi, the joe editor will be started.)

To create an installation boot diskette, insert a blank diskette and use the images/bootdisk.img file on the Red Hat Linux CD-ROM #1 with the command

Booting into Emergency Mode

In emergency mode, you are booted into the most minimal environment possible. The root file system will be mounted read-only and almost nothing will be 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 boot into emergency mode, use the same method as described for single-user mode in Section 9.3 Booting into Single-User Mode with one exception, replace the keyword «single» with the keyword «emergency».

Booting into Single-User Mode

One of the advantages of single-user mode is that you do not need a boot diskette or CD-ROM; however, it does not give you the option to mount the file systems as read-only or not mount them at all.

In single-user mode, your computer boots to runlevel 1. Your local file systems are mounted, but your network is not activated. You have a usable system maintenance shell. Unlike rescue mode, single-user mode automatically tries to mount your file system; do not use single-user mode if your file system can not be mounted successfully. You can not use single-user mode if the runlevel 1 configuration on your system is corrupted.

If your system boots, but does not allow you to log in when it has completed booting, try single-user mode.

If you are using GRUB, use the following steps to boot into single-user mode:

If you have a GRUB password configured, type p and enter the password.

Select «Red Hat Linux» with the version of the kernel that you wish to boot and type e for edit. You will be presented with a list of items in the configuration file for the title you have selected.

Select the line that starts with kernel and type e to edit the line.

Go to the end of the line and type «single» as a separate word (press the [Spacebar] and then type «single»). Press [Enter] to exit edit mode.

Back at the GRUB screen, type b to boot into single-user mode.

If you are using LILO, at the LILO boot prompt (if you are using the graphical LILO, press [Ctrl] — [x] to exit the graphical screen and go to the boot: prompt) type:

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