System information

Chapter 12. File System Check

Filesystems may be checked for consistency, and optionally repaired, with filesystem-specific

userspace tools. These tools are often referred to as fsck tools, where fsck is a shortened version

of file system check.

Note

These filesystem checkers only guarantee metadata consistency across the filesystem; they

have no awareness of the actual data contained within the filesystem and are not data

recovery tools.

Filesystem inconsistencies can occur for various reasons, including but not limited to hardware

errors, storage administration errors, and software bugs.

Before modern metadata-journaling filesystems became common, a filesystem check was required

any time a system crashed or lost power. This was because a filesystem update could have been

interrupted, leading to an inconsistent state. As a result, a filesystem check is traditionally run on

each filesystem listed in /etc/fstab at boot-time. For journaling filesystems, this is usually a very

short operation, because the filesystem's metadata journaling ensures consistency even after a

crash.

However, there are times when a filesystem inconsistency or corruption may occur, even for

journaling filesystems. When this happens, the filesystem checker must be used to repair the

filesystem. The following will provide best practices and other useful information when performing

this procedure.

Important

Red Hat does not recommend this unles the machine does not boot, the file system is extremely

large, or the file system is on remote storage. It is possible to disable file system check at boot

by setting the sixth field in /etc/fstab to 0.

12.1. Best Pract ices for fsck

Generally, running the filesystem check and repair tool can be expected to automatically repair at

least some of the inconsistencies it finds. In some cases, severely damaged inodes or directories may

be discarded if they cannot be repaired. Significant changes to the filesystem may occur. To ensure

that unexpected or undesirable changes are not permanently made, perform the following

precautionary steps:

Dry ru n

Most filesystem checkers have a mode of operation which checks but does not repair the

filesystem. In this mode, the checker will print any errors that it finds and actions that it

would have taken, without actually modifying the filesystem.

⁠Chapt er 1 2 . File Syst em Check