Emergency Mode & Filesystem Repairing

Emergency Mode

Emergency mode is similar to single-user mode except the root filesystem is mounted read-only and runlevel 1 is not used. Boot into emergency mode using the same method as single-user mode except replace the word single with emergency in the boot method.

Because the filesystem is mounted read-only, files can not be changed or repaired, but files can be retrieved off the system.

Filesystem Repair

If one or more filesystem are corrupt, boot into rescue mode and do not mount the filesystem. Even if you can boot into single-user mode, do not use it because the filesystem cannot be repaired if it is mounted.

The e2fsck utility can be used to check and repair an ext2 or ext3 (default for Red Hat Enterprise Linux) filesystem. It must be run as root, and the filesystem being checked should not be mounted. The basic syntax is as follows:

e2fsck <device>

Where <device> is the device filename for the filesystem such as /dev/hda1 for the first partition on the first IDE drive or /dev/sda2 for the second partition on the first SCSI drive. As the utility finds errors such as bad inodes, it prompts the administrator to confirm the fix. To automatically answer yes to all questions and cause the utility to be non-interactive (for example, you want to call it from a non-interactive script), use the –y command-line argument. To print verbose information while the filesystem check and repair is occurring, use the -v command-line argument. Additional arguments can be found in the e2fsck man page called from the man e2fsck command.