 fsck in action on a Linux system. | |
| Operating system | Unix and Unix-like |
|---|---|
| Type | Command |
The system utility fsck (file system check) is a tool for checking the consistency of a file system in Unix and Unix-like operating systems, such as Linux, macOS, and FreeBSD. [1] The equivalent programs on MS-DOS and Microsoft Windows are CHKDSK, SFC, and SCANDISK.
Generally, fsck is run either automatically at boot time, or manually by the system administrator. The command works directly on data structures stored on disk, which are internal and specific to the particular file system in use - so an fsck command tailored to the file system is generally required. The exact behaviors of various fsck implementations vary, but they typically follow a common order of internal operations and provide a common command-line interface to the user. On modern systems, fsck simply detects the type of filesystem and calls the specialized fsck.type (Linux) or fsck_type (BSD, macOS) program for each type. [1] [2]
Most fsck utilities provide options for either interactively repairing damaged file systems (the user must decide how to fix specific problems), automatically deciding how to fix specific problems (so the user does not have to answer any questions), or reviewing the problems that need to be resolved on a file system without actually fixing them. Partially recovered files where the original file name cannot be reconstructed are typically recovered to a "lost+found" directory that is stored at the root of the file system.
A system administrator can also run fsck manually if they believe there is a problem with the file system. The file system is normally checked while unmounted, mounted read-only, or with the system in a special maintenance mode.
As boot time fsck is expected to run without user intervention, it generally defaults to not perform any destructive operations. This may be in the form of a read-only check (failing whenever issues are found), or more commonly, a "preen" -p mode that only fixes innocuous issues commonly found after an unclean shutdown (i.e. crash, power fail). [2]
ext2/3/4 offers an option to force a boot-time check after a specified number of mounts, so that periodic checking can be done. [3]
Some modern file systems do not require fsck to be at boot after an unclean shutdown. Some examples are:
xfs_repair tool to be run when problems are suspected.-F flag used at boot. [2] btrfs-check is still available to check for suspected problems in filesystem structure (e.g. when a software bug or hardware issue is suspected).Independent of checking the file system structure, modern file systems may offer a data scrubbing tool to check for silent corruption in stored data against a mirror or a checksum. Scrubs tend to be slow as they cover all data on a disk, but periodic runs can defend against data rot and help identify failing drives. [7]
fsck first appeared in the Bell Labs "V7 addendum tape" of 1980. [8] [9] It turned into its modern wrapper form in NetBSD 1.3 (1998). fsck is not defined by any extant standard, [2] but the primitive non-wrapper form is present in the 1995 draft Systems Management: File System and Scheduling Utilities (FSSU) from X/Open. [10]
The severity of file system corruption led to the terms "fsck" and "fscked" becoming used among Unix system administrators as a minced oath for "fuck" and "fucked". [11] It is unclear whether this usage was cause or effect, as a report from a question and answer session at USENIX 1998 claims that "fsck" originally had a different name:
That story has been confirmed by Rob Pike on the Mastodon social network on December 17, 2023:
Ted Kowalski, username frodo, may he rest in peace, was the original author, just down the hall from my office in Murray Hill, and his name for the program had a 'u' where there is now an 's'. Management made him change it for distribution, but they couldn't make him change his pronunciation.
"Go fsck yourself", is occasionally used online as an injunction to a person to go and correct their issue (attitude, ignorance of the subject matter, etc.) - in the same way that running fsck involves fixing fundamental errors.
The following example checks the file system configured to be mounted on /usr partition; the file system needs to be unmounted first:
fsck/usr The following example checks the Linux JFS file system on a mdadm software RAID device:
fsck-tjfs/dev/md0 e2fsck utility, standard on many Linux distributionsXFS is a high-performance 64-bit journaling file system created by Silicon Graphics, Inc (SGI) in 1993. It was the default file system in SGI's IRIX operating system starting with its version 5.3. XFS was ported to the Linux kernel in 2001; as of June 2014, XFS is supported by most Linux distributions; Red Hat Enterprise Linux uses it as its default file system.
ext3, or third extended filesystem, is a journaled file system that is commonly used by the Linux kernel. It used to be the default file system for many popular Linux distributions. Stephen Tweedie first revealed that he was working on extending ext2 in Journaling the Linux ext2fs Filesystem in a 1998 paper, and later in a February 1999 kernel mailing list posting. The filesystem was merged with the mainline Linux kernel in November 2001 from 2.4.15 onward. Its main advantage over ext2 is journaling, which improves reliability and eliminates the need to check the file system after an unclean shutdown. Its successor is ext4.
Journaled File System (JFS) is a 64-bit journaling file system created by IBM. There are versions for AIX, OS/2, eComStation, ArcaOS and Linux operating systems. The latter is available as free software under the terms of the GNU General Public License (GPL). HP-UX has another, different filesystem named JFS that is actually an OEM version of Veritas Software's VxFS.
A disk quota is a limit set by a system administrator that restricts certain aspects of file system usage on modern operating systems. The function of using disk quotas is to allocate limited disk space in a reasonable way.
fstab is a system file commonly found in the directory /etc on Unix and Unix-like computer systems. In Linux, it is part of the util-linux package. The fstab file typically lists all available disk partitions and other types of file systems and data sources that may not necessarily be disk-based, and indicates how they are to be initialized or otherwise integrated into the larger file system structure.
In computing, a file system or filesystem governs file organization and access. A local file system is a capability of an operating system that services the applications running on the same computer. A distributed file system is a protocol that provides file access between networked computers.
In computing, mount is a command in various operating systems. Before a user can access a file on a Unix-like machine, the file system on the device which contains the file needs to be mounted with the mount command. Frequently mount is used for SD card, USB storage, DVD and other removable storage devices. The command is also available in the EFI shell.
NILFS or NILFS2 is a log-structured file system implementation for the Linux kernel. It was developed by Nippon Telegraph and Telephone Corporation (NTT) CyberSpace Laboratories and a community from all over the world. NILFS was released under the terms of the GNU General Public License (GPL).
Extended file attributes are file system features that enable users to associate computer files with metadata not interpreted by the filesystem, whereas regular attributes have a purpose strictly defined by the filesystem. Unlike forks, which can usually be as large as the maximum file size, extended attributes are usually limited in size to a value significantly smaller than the maximum file size. Typical uses include storing the author of a document, the character encoding of a plain-text document, or a checksum, cryptographic hash or digital certificate, and discretionary access control information.
Data scrubbing is an error correction technique that uses a background task to periodically inspect main memory or storage for errors, then corrects detected errors using redundant data in the form of different checksums or copies of data. Data scrubbing reduces the likelihood that single correctable errors will accumulate, leading to reduced risks of uncorrectable errors.
In Unix-like operating systems, a loop device, vnd, or lofi is a pseudo-device that makes a computer file accessible as a block device.
The following tables compare general and technical information for a number of file systems.
chattr is the command in Linux that allows a user to set certain attributes of a file. lsattr is the command that displays the attributes of a file.
Btrfs is a computer storage format that combines a file system based on the copy-on-write (COW) principle with a logical volume manager, developed together. It was created by Chris Mason in 2007 for use in Linux, and since November 2013, the file system's on-disk format has been declared stable in the Linux kernel.
Tux3 is an open-source versioning filesystem created by Daniel Phillips. He introduced the filesystem as a public replacement for his Tux2 filesystem which had encountered licensing issues due to the filing of several patents. Phillips had previously created the Htree directory indexing system which eventually became an official feature of ext3. The technical details of Tux3 were first publicized in an email on 23 July 2008.
In Unix and operating systems inspired by it, the file system is considered a central component of the operating system. It was also one of the first parts of the system to be designed and implemented by Ken Thompson in the first experimental version of Unix, dated 1969.
libguestfs is a C library and a set of tools for accessing and modifying virtual disk images used in platform virtualization. The tools can be used for viewing and editing virtual machines (VMs) managed by libvirt and files inside VMs, scripting changes to VMs, creating VMs, and much else besides. It was created because of security issues, when virtual disk images are mounted directly on the host system.
ZFS is a file system with volume management capabilities. It began as part of the Sun Microsystems Solaris operating system in 2001. Large parts of Solaris, including ZFS, were published under an open source license as OpenSolaris for around 5 years from 2005 before being placed under a closed source license when Oracle Corporation acquired Sun in 2009–2010. During 2005 to 2010, the open source version of ZFS was ported to Linux, Mac OS X and FreeBSD. In 2010, the illumos project forked a recent version of OpenSolaris, including ZFS, to continue its development as an open source project. In 2013, OpenZFS was founded to coordinate the development of open source ZFS. OpenZFS maintains and manages the core ZFS code, while organizations using ZFS maintain the specific code and validation processes required for ZFS to integrate within their systems. OpenZFS is widely used in Unix-like systems.
Stratis is a user-space configuration daemon that configures and monitors existing components from Linux's underlying storage components of logical volume management (LVM) and XFS filesystem via D-Bus.
fcking: /fus'-king/ or /eff'-seek-ing/ adj. [Usenet; common] Fucking, in the expletive sense (it refers to the Unix filesystem-repair command fsck(1), of which it can be said that if you have to use it at all you are having a bad day). Originated on {scary devil monastery} and the bofh.net newsgroups, but became much more widespread following the passage of {CDA}. Also occasionally seen in the variant 'What the fsck?'
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