fstab (after file systems table) 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.
The fstab file is read by the mount command, which happens automatically at boot time to determine the overall file system structure, and thereafter when a user executes the mount command to modify that structure. It is the duty of the system administrator to properly create and maintain the fstab file.
While fstab is used for basic system configuration, for other uses, it has been superseded by automatic mounting mechanisms.
The file has other names on some versions of Unix; for example, it is found at /etc/vfstab on Solaris systems.
The fstab file is read by programs that work with disk partitions and other file systems and is not automatically maintained. Instead it is written by the system administrator or sometimes by an operating system installation program. However, some administration tools can automatically build and edit fstab, or act as graphical editors for it.
Modern Linux systems use udev as an automounter to handle the hot swapping of devices (such as MP3 players or digital cameras) instead of relying on fstab. Programs such as pmount allow ordinary users to mount and unmount filesystems without a corresponding fstab entry; traditional Unix has always allowed privileged users (the root user and users in the wheel group) to mount or unmount devices without a corresponding fstab entry.
Example
The following is an example of an fstab file on a typical Linux system.
The order of records in fstab is important because fsck(8), mount(8), and umount(8) sequentially iterate through fstab and mount in the order defined.[1]
Blank lines and comment lines beginning with a "#" are ignored.
The space or tab-separated fields within each row must appear in a specific order:
device-spec – The device name, label, UUID, or other means of specifying the partition or data source this entry refers to.
mount-point – Where the contents of the device may be accessed after mounting; for swap partitions or files, this is set to none.
fs-type – The type of file system to be mounted.
options – Options describing various other aspects of the file system, such as whether it is automatically mounted at boot, which users may mount or access it, whether it may be written to or only read from, its size, and so forth; the special option defaults refers to a pre-determined set of options depending on the file system type.
dump – A number indicating whether and how often the file system should be backed up by the dump program; a zero indicates the file system will never be automatically backed up.
pass – A number indicating the order in which the fsck program will check the devices for errors at boot time:
0 - do not check 1 - check immediately during boot 2 - check after boot
Missing values in the last two fields are interpreted as zeros. If necessary, space characters in the first, second, and fourth fields are indicated by a @ symbol; U+0040.
Options common to all filesystems
This section contains instructions, advice, or how-to content. The purpose of Wikipedia is to present facts, not to train. Please help improve this article either by rewriting the how-to content or by moving it to Wikiversity, Wikibooks or Wikivoyage.(September 2014)
auto / noauto
With the auto option, the device will be mounted automatically at bootup or when the mount -a command is issued. auto is the default option. For the device not to be mounted automatically, the noauto option is used in /etc/fstab. With noauto, the device can be only mounted explicitly.
dev / nodev
Controls behavior of the interpretation of block special devices on the filesystem.
exec / noexec
exec lets binaries that are on the partition be executed, whereas noexec is the opposite. noexec might be useful for a partition that contains no binaries, like /var, or contains binaries the user may not want to execute on the system, or that cannot even be executed on the system, as might be the case of a Windows partition.
rw / ro
Mount the filesystem in either read write or read only mode. Explicitly defining a file system as rw can alleviate some problems in file systems that default to read only, as can be the case with floppies or NTFS partitions.
sync / async
How the input and output to the filesystem should be done. sync means it is done synchronously. Looking at the example fstab, this is the option used with the floppy. This means that when, for example, a file is copied to the floppy, the changes are physically written to the floppy at the same time copy command is issued.
suid / nosuid
Controls the behavior of the operation of suid, and sgid bits.
user / users / nouser
user permits any user to mount the filesystem. This automatically implies noexec, nosuid, nodev unless explicitly overridden. If nouser is specified, only root can mount the filesystem. If users is specified, every user in group users will be able to unmount the volume.
defaults
Use default settings. Default settings are defined per file system at the file system level. For ext3 file systems these can be set with the tune2fs command. The normal default for ext3 file systems is equivalent to rw,suid,dev,exec,auto,nouser,async. Modern Red Hat based systems set ACL support as default on the root file system but not on user-created ext3 filesystems. Some file systems such as XFS enable ACLs by default. Default file system mount attributes can be overridden in /etc/fstab.
The Unix stat structure records when files are last accessed (atime), modified (mtime), and changed (ctime). One result is that atime is written every time a file is read, which has been heavily criticized for causing performance degradation and increased wear. However, atime is used by some applications and desired by some users, and thus is configurable as atime (update on access), noatime (do not update), or (in Linux) relatime (update atime if older than mtime). Through Linux 2.6.29, atime was the default; as of 2.6.30, relatime is the default.[2]
Filesystem-specific options
There are many options for the specific filesystems supported by mount. Listed below are some of the more commonly used. The full list may be found in the documentation for mount. Note that these are for Linux; traditional Unix-like systems have generally provided similar functionality but with slightly different syntax or forms.
ext2
check=[none, normal, strict]
Sets the fsck checking level.
debug
Print debugging info on each remount.
sb=n
n is the block which should be used as the super-block for the filesystem.
FAT-only
check=[r(elaxed), n(ormal), s(trict)]
Policy for allowed filenames. See mount(8).
conv=[b(inary), t(ext), a(uto)]
Performs DOS <=> UNIX text file conversions automatically. See mount(8).
FAT, NTFS
windows_names
Linux filesystems have a larger set of allowed characters in filenames. windows_names restricts the set of allowed characters for the volume to only those acceptable by Windows; though FAT/NTFS are the most common use cases, this feature is not specifically restricted to those filesystem types.
uid=n, gid=n
Sets the user identifier (uid), and group identifier (gid) for all files on the filesystem.
umask=nnn, dmask=nnn, fmask=nnn
Controls masking of filesystem nodes.
umask - user file creation dmask - directory creation fmask - for files only
More detailed information about the fstab file can be found in the man page for Linux fstab; for other systems see below.
fstab, after, file, systems, table, system, file, commonly, found, directory, unix, unix, like, computer, systems, linux, part, util, linux, package, file, typically, lists, available, disk, partitions, other, types, file, systems, data, sources, that, necessa. fstab after file systems table 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 The fstab file is read by the a href Mount Unix html title Mount Unix mount a command which happens automatically at boot time to determine the overall file system structure and thereafter when a user executes the mount command to modify that structure It is the duty of the system administrator to properly create and maintain the fstab file While fstab is used for basic system configuration for other uses it has been superseded by automatic mounting mechanisms The file has other names on some versions of Unix for example it is found at etc vfstab on Solaris systems Contents 1 Modern use 2 Example 3 Options common to all filesystems 4 Filesystem specific options 4 1 ext2 4 2 FAT only 4 3 FAT NTFS 4 4 NFS 5 See also 6 References 7 External linksModern use EditThe fstab file is read by programs that work with disk partitions and other file systems and is not automatically maintained Instead it is written by the system administrator or sometimes by an operating system installation program However some administration tools can automatically build and edit fstab or act as graphical editors for it Modern Linux systems use udev as an automounter to handle the hot swapping of devices such as MP3 players or digital cameras instead of relying on fstab Programs such as pmount allow ordinary users to mount and unmount filesystems without a corresponding fstab entry traditional Unix has always allowed privileged users the root user and users in the wheel group to mount or unmount devices without a corresponding fstab entry Example EditThe following is an example of an fstab file on a typical Linux system device spec mount point fs type options dump pass LABEL ext4 defaults 1 1 dev sda6 none swap defaults 0 0 none dev pts devpts gid 5 mode 620 0 0 none proc proc defaults 0 0 none dev shm tmpfs defaults 0 0 Removable media dev cdrom mnt cdrom udf iso9660 noauto owner ro 0 0 NTFS Windows 7 partition dev sda1 mnt Windows ntfs 3g quiet defaults locale en US utf8 umask 0 noexec 0 0 Partition shared by Windows and Linux dev sda7 mnt shared vfat umask 000 0 0 Mounting tmpfs tmpfs mnt tmpfschk tmpfs size 100m 0 0 Mounting cifs cifs server name ashare store pingu cifs credentials root smbpass txt 0 0 Mounting NFS nfs server name store store nfs rw 0 0 The order of records in fstab is important because fsck 8 mount 8 and umount 8 sequentially iterate through fstab and mount in the order defined 1 Blank lines and comment lines beginning with a are ignored The space or tab separated fields within each row must appear in a specific order device spec The device name label UUID or other means of specifying the partition or data source this entry refers to mount point Where the contents of the device may be accessed after mounting for swap partitions or files this is set to none fs type The type of file system to be mounted options Options describing various other aspects of the file system such as whether it is automatically mounted at boot which users may mount or access it whether it may be written to or only read from its size and so forth the special option defaults refers to a pre determined set of options depending on the file system type dump A number indicating whether and how often the file system should be backed up by the dump program a zero indicates the file system will never be automatically backed up pass A number indicating the order in which the fsck program will check the devices for errors at boot time 0 do not check 1 check immediately during boot 2 check after boot Missing values in the last two fields are interpreted as zeros If necessary space characters in the first second and fourth fields are indicated by a symbol U 0040 Options common to all filesystems EditThis section contains instructions advice or how to content The purpose of Wikipedia is to present facts not to train Please help improve this article either by rewriting the how to content or by moving it to Wikiversity Wikibooks or Wikivoyage September 2014 auto noauto With the auto option the device will be mounted automatically at bootup or when the mount a command is issued auto is the default option For the device not to be mounted automatically the noauto option is used in etc fstab With noauto the device can be only mounted explicitly dev nodev Controls behavior of the interpretation of block special devices on the filesystem exec noexec exec lets binaries that are on the partition be executed whereas noexec is the opposite noexec might be useful for a partition that contains no binaries like var or contains binaries the user may not want to execute on the system or that cannot even be executed on the system as might be the case of a Windows partition rw ro Mount the filesystem in either read write or read only mode Explicitly defining a file system as rw can alleviate some problems in file systems that default to read only as can be the case with floppies or NTFS partitions sync async How the input and output to the filesystem should be done sync means it is done synchronously Looking at the example fstab this is the option used with the floppy This means that when for example a file is copied to the floppy the changes are physically written to the floppy at the same time copy command is issued suid nosuid Controls the behavior of the operation of suid and sgid bits user users nouser user permits any user to mount the filesystem This automatically implies noexec nosuid nodev unless explicitly overridden If nouser is specified only root can mount the filesystem If users is specified every user in group users will be able to unmount the volume defaults Use default settings Default settings are defined per file system at the file system level For ext3 file systems these can be set with the tune2fs command The normal default for ext3 file systems is equivalent to rw suid dev exec auto nouser async Modern Red Hat based systems set ACL support as default on the root file system but not on user created ext3 filesystems Some file systems such as XFS enable ACLs by default Default file system mount attributes can be overridden in etc fstab owner Linux specific Permit the owner of device to mount atime noatime relatime strictatime Linux specific The Unix stat structure records when files are last accessed atime modified mtime and changed ctime One result is that atime is written every time a file is read which has been heavily criticized for causing performance degradation and increased wear However atime is used by some applications and desired by some users and thus is configurable as atime update on access noatime do not update or in Linux relatime update atime if older than mtime Through Linux 2 6 29 atime was the default as of 2 6 30 relatime is the default 2 Filesystem specific options EditThere are many options for the specific filesystems supported by mount Listed below are some of the more commonly used The full list may be found in the documentation for mount Note that these are for Linux traditional Unix like systems have generally provided similar functionality but with slightly different syntax or forms ext2 Edit check none normal strict Sets the fsck checking level debug Print debugging info on each remount sb n n is the block which should be used as the super block for the filesystem FAT only Edit check r elaxed n ormal s trict Policy for allowed filenames See mount 8 conv b inary t ext a uto Performs DOS lt gt UNIX text file conversions automatically See mount 8 FAT NTFS Edit windows names Linux filesystems have a larger set of allowed characters in filenames windows names restricts the set of allowed characters for the volume to only those acceptable by Windows though FAT NTFS are the most common use cases this feature is not specifically restricted to those filesystem types uid n gid n Sets the user identifier uid and group identifier gid for all files on the filesystem umask nnn dmask nnn fmask nnn Controls masking of filesystem nodes umask user file creation dmask directory creation fmask for files only More detailed information about the fstab file can be found in the man page for Linux fstab for other systems see below NFS Edit addr ip ip is a valid IP address See also Editmount computing mount Unix mtabReferences Edit man 5 fstab Linux 2 6 30 at Linux Kernel Newbies This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Fstab news newspapers books scholar JSTOR March 2010 Learn how and when to remove this template message External links Editfstab 5 OpenBSD File Formats Manual fstab 5 NetBSD File Formats Manual fstab 5 FreeBSD File Formats Manual vfstab 4 Solaris 10 File Formats Reference Manual fstab man page from Linux fstab 5 Linux File Formats Manual fstab 5 on a Ubuntu Manpage Repository Kfstab Retrieved from https en wikipedia org w index php title Fstab amp oldid 1107577677, wikipedia, wiki, book, books, library,
