fsck is a utility to check and repair a Linux filesystem. In actuality fsck is simply a front-end for the various filesystem checkers ( fsck. fstype ) available under Linux.

Fsck is called automatically at system startup. If the filesystem is marked “not clean” , or the maximum mount count is reached or the time between checks is exceeded, the filesystem is checked. To change the maximum mount count or the time between checks, use tune2fs .

Frequently used options to fsck include:

Options which are not understood by fsck are passed to the filesystem-specific checker. These arguments(=options) must not take arguments, as there is no way for fsck to be able to properly guess which arguments take options and which don't. Options and arguments which follow the -- are treated as filesystem-specific options to be passed to the filesystem-specific checker.

The filesystem checker for the ext2 filesystem is called fsck.e2fs or e2fsck . Frequently used options include:

The mk2fs command is used to create a Linux filesystem. It can create different types of filesystems by specifying the -t filesystem or by giving the mkfs.filesystem command. Actually mkfs is a front-end for the several mkfs.fstype commands. Please read the mkfs man pages and section the section called “Creating Filesystems” for more information.

tune2fs is used to “tune” a filesystem. This is mostly used to set filesystem check options, such as the maximum mount count and the time between filesystem checks .

It is also possible to set the mount count to a specific value. This can be used to 'stagger' the mount counts of the different filesystems, which ensures that at reboot not all filesystems will be checked at the same time.

So for a system that contains 5 partitions and is booted approximately once a month you could do the following to stagger the mount counts:

					tune2fs -c 5 -C 0
					partition1
					tune2fs -c 5 -C 1
					partition2
					tune2fs -c 5 -C 2
					partition3
					tune2fs -c 5 -C 3
					partition4
					tune2fs -c 5 -C 4
					partition5
				

The maximum mount count is 20, but for a system that is not frequently rebooted a lower value is advisable.

Frequently used options include:

dumpe2fs prints the super block and blocks group information for the filesystem present on device.

badblocks is a Linux utility to check for damaged sectors on a disk drive. It marks these sectors so that they are not used in the future and thus do not cause corruption of data. It is part of the e2fsprogs project.

It is strongly recommended that badblocks not be run directly but it is to be called by using the -c option in e2fsck or mke2fs .

With debugfs , you can modify the disk with direct disk writes. Since this utility is so powerful, you will normally want to invoke it as read-only until you are ready to actually make changes and write them to the disk. To invoke debugfs in read-only mode, do not use any switches. To open in read-write mode, add the -w switch. You may also want to include in the command line the device you wish to work on, as in /dev/hda1 or /dev/sda1 , etc. Once it is invoked, you should see a debugfs prompt.

When the superblock of a partition is damaged, you can specify a different superblock to use:

					debugfs -b 1024 -s 8193 /dev/hda1
				

This means that the superblock at block 8193 will be used and the blocksize is 1024. Note that you have to specify the blocksize when you want to use a different superblock. The information about blocksize and backup superblocks can be found with:

					dumpe2fs /dev/hda1
				

The first command to try after invocation of debugfs , is params to show the mode (read-only or read-write), and the current file system. If you run this command without opening a filesystem, it will almost certainly dump core and exit. Two other commands, open and close , may be of interest when checking more than one filesystem. Close takes no argument, and appropriately enough, it closes the filesystem that is currently open. Open takes the device name as an argument. To see disk statistics from the superblock, the command stats will display the information by group. The command testb checks whether a block is in use. This can be used to test if any data is lost in the blocks marked as “ bad ” by the badblocks command. To get the filename for a block, first use the icheck command to get the inode and then ncheck to get the filename. The best course of action with bad blocks is to mark the block “bad ” and restore the file from backup.

To get a complete list of all commands, see the man page of debugfs or type ? , lr or list_requests .

The debugging tool for the ReiserFS filesystem. It has about the same functionality as debugfs but only for the ReiserFS filesystem.

The tuning tool for the ReiserFS filesystem. It has about the same functionality as tune2fs but only for the ReiserFS filesystem.

mkswap sets up a Linux swap area on a device or in a file. (After creating the swap area, you need to invoke the swapon command to start using it. Usually swap areas are listed in /etc/fstab so that they can be taken into use at boot time by a swapon -a command in some boot script.)

xfs_info shows the filesystem geometry. xfs_info is equivalent to invoking xfs_growfs with the -n option.

xfs_check checks whether an XFS filesystem is consistent. It is normally run only when there is reason to believe that the filesystem has a consistency problem.

xfs_repair repairs corrupt or damaged XFS filesystems. xfs_repair will attempt to find the raw device associated with the specified block device and will use the raw device instead. Regardless, the filesystem to be repaired must be unmounted, otherwise, the resulting filesystem may become inconsistent or corrupt.