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diff --git a/sys-utils/mount.8 b/sys-utils/mount.8 new file mode 100644 index 0000000..da0ac5b --- /dev/null +++ b/sys-utils/mount.8 @@ -0,0 +1,2589 @@ +.\" Copyright (c) 1996-2004 Andries Brouwer +.\" Copyright (C) 2006-2012 Karel Zak <kzak@redhat.com> +.\" +.\" This page is somewhat derived from a page that was +.\" (c) 1980, 1989, 1991 The Regents of the University of California +.\" and had been heavily modified by Rik Faith and myself. +.\" (Probably no BSD text remains.) +.\" Fragments of text were written by Werner Almesberger, Remy Card, +.\" Stephen Tweedie and Eric Youngdale. +.\" +.\" This is free documentation; you can redistribute it and/or +.\" modify it under the terms of the GNU General Public License as +.\" published by the Free Software Foundation; either version 2 of +.\" the License, or (at your option) any later version. +.\" +.\" The GNU General Public License's references to "object code" +.\" and "executables" are to be interpreted as the output of any +.\" document formatting or typesetting system, including +.\" intermediate and printed output. +.\" +.\" This manual is distributed in the hope that it will be useful, +.\" but WITHOUT ANY WARRANTY; without even the implied warranty of +.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +.\" GNU General Public License for more details. +.\" +.\" You should have received a copy of the GNU General Public License along +.\" with this program; if not, write to the Free Software Foundation, Inc., +.\" 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. +.\" +.TH MOUNT 8 "August 2015" "util-linux" "System Administration" +.SH NAME +mount \- mount a filesystem +.SH SYNOPSIS +.B mount +.RB [ \-l | \-h | \-V ] +.LP +.B mount \-a +.RB [ \-fFnrsvw ] +.RB [ \-t +.IR fstype ] +.RB [ \-O +.IR optlist ] +.LP +.B mount +.RB [ \-fnrsvw ] +.RB [ \-o +.IR options ] +.IR device | dir +.LP +.B mount +.RB [ \-fnrsvw ] +.RB [ \-t +.IB fstype ] +.RB [ \-o +.IR options ] +.I device dir +.SH DESCRIPTION +All files accessible in a Unix system are arranged in one big +tree, the file hierarchy, rooted at +.IR / . +These files can be spread out over several devices. The +.B mount +command serves to attach the filesystem found on some device +to the big file tree. Conversely, the +.BR umount (8) +command will detach it again. The filesystem is used to control how data is +stored on the device or provided in a virtual way by network or another services. + +The standard form of the +.B mount +command is: +.RS + +.br +.BI "mount \-t" " type device dir" +.br + +.RE +This tells the kernel to attach the filesystem found on +.I device +(which is of type +.IR type ) +at the directory +.IR dir . +The option \fB\-t \fItype\fR is optional. The +.B mount +command is usually able to detect a filesystem. The root permissions are necessary +to mount a filesystem by default. See section "Non-superuser mounts" below for more details. +The previous contents (if any) and owner and mode of +.I dir +become invisible, and as long as this filesystem remains mounted, +the pathname +.I dir +refers to the root of the filesystem on +.IR device . + +If only the directory or the device is given, for example: +.RS +.sp +.B mount /dir +.sp +.RE +then \fBmount\fR looks for a mountpoint (and if not found then for a device) in the +.I /etc/fstab +file. It's possible to use the +.B \-\-target +or +.B \-\-source +options to avoid ambivalent interpretation of the given argument. For example: +.RS +.sp +.B mount \-\-target /mountpoint +.sp +.RE + +The same filesystem may be mounted more than once, and in some cases (e.g. +network filesystems) the same filesystem maybe be mounted on the same +mountpoint more times. The mount command does not implement any policy to +control this behavior. All behavior is controlled by kernel and it is usually +specific to filesystem driver. The exception is \fB\-\-all\fR, in this case +already mounted filesystems are ignored (see \fB\-\-all\fR below for more details). + +.SS Listing the mounts +The listing mode is maintained for backward compatibility only. + +For more robust and customizable output use +.BR findmnt (8), +\fBespecially in your scripts\fP. Note that control characters in the +mountpoint name are replaced with '?'. + +The following command lists all mounted filesystems (of type +.IR type ): +.RS +.sp +.BR "mount " [ \-l "] [" "\-t \fItype\/\fP" ] +.sp +.RE +The option \fB\-l\fR adds labels to this listing. See below. + +.SS Indicating the device and filesystem +Most devices are indicated by a filename (of a block special device), like +.IR /dev/sda1 , +but there are other possibilities. For example, in the case of an NFS mount, +.I device +may look like +.IR knuth.cwi.nl:/dir . +It is also possible to indicate a block special device using its filesystem label +or UUID (see the \fB\-L\fR and \fB\-U\fR options below), or its partition label +or UUID. Partition identifiers are supported for example for GUID Partition +Tables (GPT). + +The device name of disk partitions are unstable; hardware reconfiguration, +adding or removing a device can cause change in names. This is reason why it's +strongly recommended to use filesystem or partition identificators like UUID or +LABEL. + +The command \fBlsblk --fs\fR provides overview of filesystems, LABELs and UUIDs +on available block devices. The command \fBblkid -p <device>\fR provides details about +a filesystem on the specified device. + +Don't forget that there is no guarantee that UUIDs and labels are really +unique, especially if you move, share or copy the device. Use +.B "lsblk \-o +UUID,PARTUUID" +to verify that the UUIDs are really unique in your system. + +The recommended setup is to use tags (e.g.\& \fBUUID=\fIuuid\fR) rather than +.I /dev/disk/by-{label,uuid,partuuid,partlabel} +udev symlinks in the +.I /etc/fstab +file. Tags are +more readable, robust and portable. The +.BR mount (8) +command internally uses udev +symlinks, so the use of symlinks in /etc/fstab has no advantage over tags. +For more details see +.BR libblkid (3). + +Note that +.BR mount (8) +uses UUIDs as strings. The UUIDs from the command line or from +.BR fstab (5) +are not converted to internal binary representation. The string representation +of the UUID should be based on lower case characters. + +The +.I proc +filesystem is not associated with a special device, and when +mounting it, an arbitrary keyword, such as +.I proc +can be used instead of a device specification. +(The customary choice +.I none +is less fortunate: the error message `none already mounted' from +.B mount +can be confusing.) + +.SS The files /etc/fstab, /etc/mtab and /proc/mounts +The file +.I /etc/fstab +(see +.BR fstab (5)), +may contain lines describing what devices are usually +mounted where, using which options. The default location of the +.BR fstab (5) +file can be overridden with the +.BI \-\-fstab " path" +command-line option (see below for more details). +.LP +The command +.RS +.sp +.B mount \-a +.RB [ \-t +.IR type ] +.RB [ \-O +.IR optlist ] +.sp +.RE +(usually given in a bootscript) causes all filesystems mentioned in +.I fstab +(of the proper type and/or having or not having the proper options) +to be mounted as indicated, except for those whose line contains the +.B noauto +keyword. Adding the +.B \-F +option will make \fBmount\fR fork, so that the +filesystems are mounted simultaneously. +.LP +When mounting a filesystem mentioned in +.I fstab +or +.IR mtab , +it suffices to specify on the command line only the device, or only the mount point. +.sp +The programs +.B mount +and +.B umount +traditionally maintained a list of currently mounted filesystems in the file +.IR /etc/mtab . +The support for regular classic +.I /etc/mtab +is completely disabled in compile time by default, because on current Linux +systems it is better to make it a symlink to +.I /proc/mounts +instead. The regular mtab file maintained in userspace cannot reliably +work with namespaces, containers and other advanced Linux features. +If the regular mtab support is enabled than it's possible to +use the file as well as the symlink. +.sp +If no arguments are given to +.BR mount , +the list of mounted filesystems is printed. +.sp +If you want to override mount options from +.I /etc/fstab +you have to use the \fB\-o\fR option: +.RS +.sp +.BI mount " device" \fR| "dir " \-o " options" +.sp +.RE +and then the mount options from the command line will be appended to +the list of options from +.IR /etc/fstab . +This default behaviour is possible to change by command line +option \fB\-\-options\-mode\fR. +The usual behavior is that the last option wins if there are conflicting +ones. +.sp +The +.B mount +program does not read the +.I /etc/fstab +file if both +.I device +(or LABEL, UUID, PARTUUID or PARTLABEL) and +.I dir +are specified. For example, to mount device +.BR foo " at " /dir : +.RS +.sp +.B "mount /dev/foo /dir" +.sp +.RE +This default behaviour is possible to change by command line option +\fB\-\-options\-source\-force\fR to always read configuration from fstab. For +non-root users +.B mount +always read fstab configuration. + +.SS Non-superuser mounts +Normally, only the superuser can mount filesystems. +However, when +.I fstab +contains the +.B user +option on a line, anybody can mount the corresponding filesystem. +.LP +Thus, given a line +.RS +.sp +.B "/dev/cdrom /cd iso9660 ro,user,noauto,unhide" +.sp +.RE +any user can mount the iso9660 filesystem found on an inserted CDROM +using the command: +.RS +.B "mount /cd" +.sp +.RE +Note that \fBmount\fR is very strict about non-root users and all paths +specified on command line are verified before fstab is parsed or a helper +program is executed. It's strongly recommended to use a valid mountpoint to +specify filesystem, otherwise \fBmount\fR may fail. For example it's bad idea +to use NFS or CIFS source on command line. +.PP +For more details, see +.BR fstab (5). +Only the user that mounted a filesystem can unmount it again. +If any user should be able to unmount it, then use +.B users +instead of +.B user +in the +.I fstab +line. +The +.B owner +option is similar to the +.B user +option, with the restriction that the user must be the owner +of the special file. This may be useful e.g.\& for +.I /dev/fd +if a login script makes the console user owner of this device. +The +.B group +option is similar, with the restriction that the user must be +member of the group of the special file. + +.SS Bind mount operation +Remount part of the file hierarchy somewhere else. The call is: + +.RS +.br +.B mount \-\-bind +.I olddir newdir +.RE + +or by using this fstab entry: + +.RS +.br +.BI / olddir +.BI / newdir +.B none bind +.RE + +After this call the same contents are accessible in two places. + +It is important to understand that "bind" does not to create any second-class +or special node in the kernel VFS. The "bind" is just another operation to +attach a filesystem. There is nowhere stored information that the filesystem +has been attached by "bind" operation. The \fIolddir\fR and \fInewdir\fR are +independent and the \fIolddir\fR maybe be umounted. + +One can also remount a single file (on a single file). It's also +possible to use the bind mount to create a mountpoint from a regular +directory, for example: + +.RS +.br +.B mount \-\-bind foo foo +.RE + +The bind mount call attaches only (part of) a single filesystem, not possible +submounts. The entire file hierarchy including submounts is attached +a second place by using: + +.RS +.br +.B mount \-\-rbind +.I olddir newdir +.RE + +Note that the filesystem mount options maintained by kernel will remain the same as those +on the original mount point. The userspace mount options (e.g. _netdev) will not be copied +by +.BR mount (8) +and it's necessary explicitly specify the options on mount command line. + +.BR mount (8) +since v2.27 allows to change the mount options by passing the +relevant options along with +.BR \-\-bind . +For example: + +.RS +.br +.B mount -o bind,ro foo foo +.RE + +This feature is not supported by the Linux kernel; it is implemented in userspace +by an additional \fBmount\fR(2) remounting system call. +This solution is not atomic. + +The alternative (classic) way to create a read-only bind mount is to use the remount +operation, for example: + +.RS +.br +.B mount \-\-bind +.I olddir newdir +.br +.B mount \-o remount,bind,ro +.I olddir newdir +.RE + +Note that a read-only bind will create a read-only mountpoint (VFS entry), +but the original filesystem superblock will still be writable, meaning that the +.I olddir +will be writable, but the +.I newdir +will be read-only. + +It's also possible to change nosuid, nodev, noexec, noatime, nodiratime and +relatime VFS entry flags by "remount,bind" operation. The another (for example +filesystem specific flags) are silently ignored. It's impossible to change mount +options recursively (for example with \fB-o rbind,ro\fR). + +.BR mount (8) +since v2.31 ignores the \fBbind\fR flag from +.I /etc/fstab +on +.B remount operation +(if "-o remount" specified on command line). This is necessary to fully control +mount options on remount by command line. In the previous versions the bind +flag has been always applied and it was impossible to re-define mount options +without interaction with the bind semantic. This +.BR mount (8) +behavior does not affect situations when "remount,bind" is specified in the +.I /etc/fstab +file. +.RE + +.SS The move operation +Move a +.B mounted tree +to another place (atomically). The call is: + +.RS +.br +.B mount \-\-move +.I olddir newdir +.RE + +This will cause the contents which previously appeared under +.I olddir +to now be accessible under +.IR newdir . +The physical location of the files is not changed. +Note that +.I olddir +has to be a mountpoint. + +Note also that moving a mount residing under a shared mount is invalid and +unsupported. Use +.B findmnt \-o TARGET,PROPAGATION +to see the current propagation flags. + +.SS Shared subtree operations +Since Linux 2.6.15 it is possible to mark a mount and its submounts as shared, +private, slave or unbindable. A shared mount provides the ability to create mirrors +of that mount such that mounts and unmounts within any of the mirrors propagate +to the other mirror. A slave mount receives propagation from its master, but +not vice versa. A private mount carries no propagation abilities. An +unbindable mount is a private mount which cannot be cloned through a bind +operation. The detailed semantics are documented in +.I Documentation/filesystems/sharedsubtree.txt +file in the kernel source tree. + +Supported operations are: + +.RS +.nf +.BI "mount \-\-make\-shared " mountpoint +.BI "mount \-\-make\-slave " mountpoint +.BI "mount \-\-make\-private " mountpoint +.BI "mount \-\-make\-unbindable " mountpoint +.fi +.RE + +The following commands allow one to recursively change the type of all the +mounts under a given mountpoint. + +.RS +.nf +.BI "mount \-\-make\-rshared " mountpoint +.BI "mount \-\-make\-rslave " mountpoint +.BI "mount \-\-make\-rprivate " mountpoint +.BI "mount \-\-make\-runbindable " mountpoint +.fi +.RE + +.BR mount (8) +.B does not read +.BR fstab (5) +when a \fB\-\-make-\fR* operation is requested. All necessary information has to be +specified on the command line. + +Note that the Linux kernel does not allow to change multiple propagation flags +with a single +.BR mount (2) +system call, and the flags cannot be mixed with other mount options and operations. + +Since util-linux 2.23 the \fBmount\fR command allows to do more propagation +(topology) changes by one mount(8) call and do it also together with other +mount operations. This feature is EXPERIMENTAL. The propagation flags are applied +by additional \fBmount\fR(2) system calls when the preceding mount operations +were successful. Note that this use case is not atomic. It is possible to +specify the propagation flags in +.BR fstab (5) +as mount options +.RB ( private , +.BR slave , +.BR shared , +.BR unbindable , +.BR rprivate , +.BR rslave , +.BR rshared , +.BR runbindable ). + +For example: + +.RS +.nf +.B mount \-\-make\-private \-\-make\-unbindable /dev/sda1 /foo +.fi +.RE + +is the same as: + +.RS +.nf +.B mount /dev/sda1 /foox +.B mount \-\-make\-private /foo +.B mount \-\-make\-unbindable /foo +.fi +.RE + +.SH COMMAND-LINE OPTIONS +The full set of mount options used by an invocation of +.B mount +is determined by first extracting the +mount options for the filesystem from the +.I fstab +table, then applying any options specified by the +.B \-o +argument, and finally applying a +.BR \-r " or " \-w +option, when present. + +The command \fBmount\fR does not pass all command-line options to the +\fB/sbin/mount.\fIsuffix\fR mount helpers. The interface between \fBmount\fR +and the mount helpers is described below in the section \fBEXTERNAL HELPERS\fR. +.sp +Command-line options available for the +.B mount +command are: +.TP +.BR \-a , " \-\-all" +Mount all filesystems (of the given types) mentioned in +.I fstab +(except for those whose line contains the +.B noauto +keyword). The filesystems are mounted following their order in +.IR fstab . +The mount command compares filesystem source, target (and fs root for bind +mount or btrfs) to detect already mounted filesystems. The kernel table with +already mounted filesystems is cached during \fBmount \-\-all\fR. It means +that all duplicated fstab entries will be mounted. +.sp +Note that it is a bad practice to use \fBmount \-a\fR for +.I fstab +checking. The recommended solution is \fBfindmnt \-\-verify\fR. +.TP +.BR \-B , " \-\-bind" +Remount a subtree somewhere else (so that its contents are available +in both places). See above, under \fBBind mounts\fR. +.TP +.BR \-c , " \-\-no\-canonicalize" +Don't canonicalize paths. The mount command canonicalizes all paths +(from command line or fstab) by default. This option can be used +together with the +.B \-f +flag for already canonicalized absolute paths. The option is designed for mount +helpers which call \fBmount -i\fR. It is strongly recommended to not use this +command-line option for normal mount operations. +.sp +Note that \fBmount\fR(8) does not pass this option to the +\fB/sbin/mount.\fItype\fR helpers. +.TP +.BR \-F , " \-\-fork" +(Used in conjunction with +.BR \-a .) +Fork off a new incarnation of \fBmount\fR for each device. +This will do the mounts on different devices or different NFS servers +in parallel. +This has the advantage that it is faster; also NFS timeouts go in +parallel. A disadvantage is that the mounts are done in undefined order. +Thus, you cannot use this option if you want to mount both +.I /usr +and +.IR /usr/spool . +.IP "\fB\-f, \-\-fake\fP" +Causes everything to be done except for the actual system call; if it's not +obvious, this ``fakes'' mounting the filesystem. This option is useful in +conjunction with the +.B \-v +flag to determine what the +.B mount +command is trying to do. It can also be used to add entries for devices +that were mounted earlier with the \fB\-n\fR option. The \fB\-f\fR option +checks for an existing record in /etc/mtab and fails when the record already +exists (with a regular non-fake mount, this check is done by the kernel). +.IP "\fB\-i, \-\-internal\-only\fP" +Don't call the \fB/sbin/mount.\fIfilesystem\fR helper even if it exists. +.TP +.BR \-L , " \-\-label " \fIlabel +Mount the partition that has the specified +.IR label . +.TP +.BR \-l , " \-\-show\-labels" +Add the labels in the mount output. \fBmount\fR must have +permission to read the disk device (e.g.\& be set-user-ID root) for this to work. +One can set such a label for ext2, ext3 or ext4 using the +.BR e2label (8) +utility, or for XFS using +.BR xfs_admin (8), +or for reiserfs using +.BR reiserfstune (8). +.TP +.BR \-M , " \-\-move" +Move a subtree to some other place. See above, the subsection +\fBThe move operation\fR. +.TP +.BR \-n , " \-\-no\-mtab" +Mount without writing in +.IR /etc/mtab . +This is necessary for example when +.I /etc +is on a read-only filesystem. +.TP +.BR \-N , " \-\-namespace " \fIns +Perform mount in namespace specified by \fIns\fR. +\fIns\fR is either PID of process running in that namespace +or special file representing that namespace. +.sp +.BR mount (8) +switches to the namespace when it reads /etc/fstab, writes /etc/mtab (or writes to /run/mount) and calls +.BR mount (2) +system call, otherwise it runs in the original namespace. It means that the target namespace does not have +to contain any libraries or another requirements necessary to execute +.BR mount (2) +command. +.sp +See \fBnamespaces\fR(7) for more information. +.TP +.BR \-O , " \-\-test\-opts " \fIopts +Limit the set of filesystems to which the +.B \-a +option applies. In this regard it is like the +.B \-t +option except that +.B \-O +is useless without +.BR \-a . +For example, the command: +.RS +.RS +.sp +.B "mount \-a \-O no_netdev" +.sp +.RE +mounts all filesystems except those which have the option +.I _netdev +specified in the options field in the +.I /etc/fstab +file. + +It is different from +.B \-t +in that each option is matched exactly; a leading +.B no +at the beginning of one option does not negate the rest. + +The +.B \-t +and +.B \-O +options are cumulative in effect; that is, the command +.RS +.sp +.B "mount \-a \-t ext2 \-O _netdev" +.sp +.RE +mounts all ext2 filesystems with the _netdev option, not all filesystems +that are either ext2 or have the _netdev option specified. +.RE +.TP +.BR \-o , " \-\-options " \fIopts +Use the specified mount options. The \fIopts\fR argument is +a comma-separated list. For example: +.RS +.RS +.sp +.B "mount LABEL=mydisk \-o noatime,nodev,nosuid" +.sp +.RE + +For more details, see the +.B FILESYSTEM-INDEPENDENT MOUNT OPTIONS +and +.B FILESYSTEM-SPECIFIC MOUNT OPTIONS +sections. +.RE + +.TP +.BR "\-\-options\-mode " \fImode +Controls how to combine options from fstab/mtab with options from command line. +\fImode\fR can be one of +.BR ignore ", " append ", " prepend " or " replace . +For example \fBappend\fR means that options from fstab are appended to options from command line. +Default value is \fBprepend\fR -- it means command line options are evaluated after fstab options. +Note that the last option wins if there are conflicting ones. + +.TP +.BR "\-\-options\-source " \fIsource +Source of default options. +\fIsource\fR is comma separated list of +.BR fstab ", " mtab " and " disable . +\fBdisable\fR disables +.BR fstab " and " mtab +and disables \fB\-\-options\-source\-force\fR. +Default value is \fBfstab,mtab\fR. + +.TP +.B \-\-options\-source\-force +Use options from fstab/mtab even if both \fIdevice\fR and \fIdir\fR are specified. + +.TP +.BR \-R , " \-\-rbind" +Remount a subtree and all possible submounts somewhere else (so that its +contents are available in both places). See above, the subsection +\fBBind mounts\fR. +.TP +.BR \-r , " \-\-read\-only" +Mount the filesystem read-only. A synonym is +.BR "\-o ro" . +.sp +Note that, depending on the filesystem type, state and kernel behavior, the +system may still write to the device. For example, ext3 and ext4 will replay the +journal if the filesystem is dirty. To prevent this kind of write access, you +may want to mount an ext3 or ext4 filesystem with the \fBro,noload\fR mount +options or set the block device itself to read-only mode, see the +.BR blockdev (8) +command. +.TP +.B \-s +Tolerate sloppy mount options rather than failing. This will ignore mount +options not supported by a filesystem type. Not all filesystems support this +option. Currently it's supported by the \fBmount.nfs\fR mount helper only. +.TP +.BI \-\-source " device" +If only one argument for the mount command is given then the argument might be +interpreted as target (mountpoint) or source (device). This option allows to +explicitly define that the argument is the mount source. +.TP +.BI \-\-target " directory" +If only one argument for the mount command is given then the argument might be +interpreted as target (mountpoint) or source (device). This option allows to +explicitly define that the argument is the mount target. +.TP +.BR \-T , " \-\-fstab " \fIpath +Specifies an alternative fstab file. If \fIpath\fP is a directory then the files +in the directory are sorted by +.BR strverscmp (3); +files that start with "."\& or without an \&.fstab extension are ignored. The option +can be specified more than once. This option is mostly designed for initramfs +or chroot scripts where additional configuration is specified beyond standard +system configuration. +.sp +Note that \fBmount\fR(8) does not pass the option \fB\-\-fstab\fP to the +\fB/sbin/mount.\fItype\fR helpers, meaning that the alternative fstab files will be +invisible for the helpers. This is no problem for normal mounts, but user +(non-root) mounts always require fstab to verify the user's rights. +.TP +.BR \-t , " \-\-types " \fIfstype +The argument following the +.B \-t +is used to indicate the filesystem type. The filesystem types which are +currently supported depend on the running kernel. See +.I /proc/filesystems +and +.I /lib/modules/$(uname -r)/kernel/fs +for a complete list of the filesystems. The most common are ext2, ext3, ext4, +xfs, btrfs, vfat, sysfs, proc, nfs and cifs. +.sp +The programs +.B mount +and +.B umount +support filesystem subtypes. The subtype is defined by a '.subtype' suffix. For +example 'fuse.sshfs'. It's recommended to use subtype notation rather than add +any prefix to the mount source (for example 'sshfs#example.com' is +deprecated). + +If no +.B \-t +option is given, or if the +.B auto +type is specified, mount will try to guess the desired type. +Mount uses the blkid library for guessing the filesystem +type; if that does not turn up anything that looks familiar, +mount will try to read the file +.IR /etc/filesystems , +or, if that does not exist, +.IR /proc/filesystems . +All of the filesystem types listed there will be tried, +except for those that are labeled "nodev" (e.g.\& +.IR devpts , +.I proc +and +.IR nfs ). +If +.I /etc/filesystems +ends in a line with a single *, mount will read +.I /proc/filesystems +afterwards. While trying, all filesystem types will be +mounted with the mount option \fBsilent\fR. +.sp +The +.B auto +type may be useful for user-mounted floppies. +Creating a file +.I /etc/filesystems +can be useful to change the probe order (e.g., to try vfat before msdos +or ext3 before ext2) or if you use a kernel module autoloader. +.sp +More than one type may be specified in a comma-separated +list, for option +.B \-t +as well as in an +.I /etc/fstab +entry. The list of filesystem types for option +.B \-t +can be prefixed with +.B no +to specify the filesystem types on which no action should be taken. +The prefix +.B no +has no effect when specified in an +.I /etc/fstab +entry. +.sp +The prefix +.B no +can be meaningful with the +.B \-a +option. For example, the command +.RS +.RS +.sp +.B "mount \-a \-t nomsdos,smbfs" +.sp +.RE +mounts all filesystems except those of type +.I msdos +and +.IR smbfs . +.sp +For most types all the +.B mount +program has to do is issue a simple +.BR mount (2) +system call, and no detailed knowledge of the filesystem type is required. +For a few types however (like nfs, nfs4, cifs, smbfs, ncpfs) an ad hoc code is +necessary. The nfs, nfs4, cifs, smbfs, and ncpfs filesystems +have a separate mount program. In order to make it possible to +treat all types in a uniform way, \fBmount\fR will execute the program +.BI /sbin/mount. type +(if that exists) when called with type +.IR type . +Since different versions of the +.B smbmount +program have different calling conventions, +.B /sbin/mount.smbfs +may have to be a shell script that sets up the desired call. +.RE +.TP +.BR \-U , " \-\-uuid " \fIuuid +Mount the partition that has the specified +.IR uuid . +.TP +.BR \-v , " \-\-verbose" +Verbose mode. +.TP +.BR \-w , " \-\-rw" , " \-\-read\-write" +Mount the filesystem read/write. The read-write is kernel default. A synonym is +.BR "\-o rw" . + +Note that specify \fB\-w\fR on command line forces \fBmount\fR command +to never try read-only mount on write-protected devices. The default is +try read-only if the previous mount syscall with read-write flags failed. +.TP +.BR \-V , " \-\-version" +Display version information and exit. +.TP +.BR \-h , " \-\-help" +Display help text and exit. + +.SH FILESYSTEM-INDEPENDENT MOUNT OPTIONS +Some of these options are only useful when they appear in the +.I /etc/fstab +file. + +Some of these options could be enabled or disabled by default +in the system kernel. To check the current setting see the options +in /proc/mounts. Note that filesystems also have per-filesystem +specific default mount options (see for example \fBtune2fs \-l\fP +output for extN filesystems). + +The following options apply to any filesystem that is being +mounted (but not every filesystem actually honors them \(en e.g.\&, the +.B sync +option today has an effect only for ext2, ext3, ext4, fat, vfat and ufs): + +.TP +.B async +All I/O to the filesystem should be done asynchronously. (See also the +.B sync +option.) +.TP +.B atime +Do not use the \fBnoatime\fR feature, so the inode access time is controlled +by kernel defaults. See also the descriptions of the \fB\%relatime\fR and +.B strictatime +mount options. +.TP +.B noatime +Do not update inode access times on this filesystem (e.g.\& for faster +access on the news spool to speed up news servers). This works for all +inode types (directories too), so it implies \fB\%nodiratime\fR. +.TP +.B auto +Can be mounted with the +.B \-a +option. +.TP +.B noauto +Can only be mounted explicitly (i.e., the +.B \-a +option will not cause the filesystem to be mounted). +.TP +.na +.BR context=\fIcontext ", " fscontext=\fIcontext ", " defcontext=\fIcontext ", and " \%rootcontext=\fIcontext +.ad +The +.B context= +option is useful when mounting filesystems that do not support +extended attributes, such as a floppy or hard disk formatted with VFAT, or +systems that are not normally running under SELinux, such as an ext3 or ext4 formatted + +disk from a non-SELinux workstation. You can also use +.B context= +on filesystems you do not trust, such as a floppy. It also helps in compatibility with +xattr-supporting filesystems on earlier 2.4.<x> kernel versions. Even where +xattrs are supported, you can save time not having to label every file by +assigning the entire disk one security context. + +A commonly used option for removable media is +.BR \%context="system_u:object_r:removable_t" . + +Two other options are +.B fscontext= +and +.BR defcontext= , +both of which are mutually exclusive of the context option. This means you +can use fscontext and defcontext with each other, but neither can be used with +context. + +The +.B fscontext= +option works for all filesystems, regardless of their xattr +support. The fscontext option sets the overarching filesystem label to a +specific security context. This filesystem label is separate from the +individual labels on the files. It represents the entire filesystem for +certain kinds of permission checks, such as during mount or file creation. +Individual file labels are still obtained from the xattrs on the files +themselves. The context option actually sets the aggregate context that +fscontext provides, in addition to supplying the same label for individual +files. + +You can set the default security context for unlabeled files using +.B defcontext= +option. This overrides the value set for unlabeled files in the policy and requires a +filesystem that supports xattr labeling. + +The +.B rootcontext= +option allows you to explicitly label the root inode of a FS being mounted +before that FS or inode becomes visible to userspace. This was found to be +useful for things like stateless linux. + +Note that the kernel rejects any remount request that includes the context +option, \fBeven\fP when unchanged from the current context. + +.BR "Warning: the \fIcontext\fP value might contain commas" , +in which case the value has to be properly quoted, otherwise +.BR mount (8) +will interpret the comma as a separator between mount options. Don't forget that +the shell strips off quotes and thus +.BR "double quoting is required" . +For example: +.RS +.RS +.sp +.nf +.B mount \-t tmpfs none /mnt \-o \e +.B \ \ 'context="system_u:object_r:tmp_t:s0:c127,c456",noexec' +.fi +.sp +.RE +For more details, see +.BR selinux (8). +.RE + +.TP +.B defaults +Use the default options: +.BR rw ", " suid ", " dev ", " exec ", " auto ", " nouser ", and " async . + +Note that the real set of all default mount options depends on kernel +and filesystem type. See the beginning of this section for more details. +.TP +.B dev +Interpret character or block special devices on the filesystem. +.TP +.B nodev +Do not interpret character or block special devices on the file +system. +.TP +.B diratime +Update directory inode access times on this filesystem. This is the default. +(This option is ignored when \fBnoatime\fR is set.) +.TP +.B nodiratime +Do not update directory inode access times on this filesystem. +(This option is implied when \fBnoatime\fR is set.) +.TP +.B dirsync +All directory updates within the filesystem should be done synchronously. +This affects the following system calls: creat, link, unlink, symlink, +mkdir, rmdir, mknod and rename. +.TP +.B exec +Permit execution of binaries. +.TP +.B noexec +Do not permit direct execution of any binaries on the mounted filesystem. +.TP +.B group +Allow an ordinary user to mount the filesystem if one +of that user's groups matches the group of the device. +This option implies the options +.BR nosuid " and " nodev +(unless overridden by subsequent options, as in the option line +.BR group,dev,suid ). +.TP +.B iversion +Every time the inode is modified, the i_version field will be incremented. +.TP +.B noiversion +Do not increment the i_version inode field. +.TP +.B mand +Allow mandatory locks on this filesystem. See +.BR fcntl (2). +.TP +.B nomand +Do not allow mandatory locks on this filesystem. +.TP +.B _netdev +The filesystem resides on a device that requires network access +(used to prevent the system from attempting to mount these filesystems +until the network has been enabled on the system). +.TP +.B nofail +Do not report errors for this device if it does not exist. +.TP +.B relatime +Update inode access times relative to modify or change time. Access +time is only updated if the previous access time was earlier than the +current modify or change time. (Similar to \fB\%noatime\fR, but it doesn't +break \fBmutt\fR or other applications that need to know if a file has been +read since the last time it was modified.) + +Since Linux 2.6.30, the kernel defaults to the behavior provided by this +option (unless +.B \%noatime +was specified), and the +.B \%strictatime +option is required to obtain traditional semantics. In addition, since Linux +2.6.30, the file's last access time is always updated if it is more than 1 +day old. +.TP +.B norelatime +Do not use the +.B relatime +feature. See also the +.B strictatime +mount option. +.TP +.B strictatime +Allows to explicitly request full atime updates. This makes it +possible for the kernel to default to +.B \%relatime +or +.B \%noatime +but still allow userspace to override it. For more details about the default +system mount options see /proc/mounts. +.TP +.B nostrictatime +Use the kernel's default behavior for inode access time updates. +.TP +.B lazytime +Only update times (atime, mtime, ctime) on the in-memory version of the file inode. + +This mount option significantly reduces writes to the inode table for +workloads that perform frequent random writes to preallocated files. + +The on-disk timestamps are updated only when: +.sp +.RS +- the inode needs to be updated for some change unrelated to file timestamps +.sp +- the application employs +.BR fsync (2), +.BR syncfs (2), +or +.BR sync (2) +.sp +- an undeleted inode is evicted from memory +.sp +- more than 24 hours have passed since the i-node was written to disk. +.RE +.sp +.TP +.B nolazytime +Do not use the lazytime feature. +.TP +.B suid +Allow set-user-ID or set-group-ID bits to take +effect. +.TP +.B nosuid +Do not allow set-user-ID or set-group-ID bits to take +effect. +.TP +.B silent +Turn on the silent flag. +.TP +.B loud +Turn off the silent flag. +.TP +.B owner +Allow an ordinary user to mount the filesystem if that +user is the owner of the device. +This option implies the options +.BR nosuid " and " nodev +(unless overridden by subsequent options, as in the option line +.BR owner,dev,suid ). +.TP +.B remount +Attempt to remount an already-mounted filesystem. This is commonly +used to change the mount flags for a filesystem, especially to make a +readonly filesystem writable. It does not change device or mount point. + +The remount operation together with the +.B bind +flag has special semantic. See above, the subsection \fBBind mounts\fR. + +The remount functionality follows the standard way the mount command works +with options from fstab. This means that \fBmount\fR does not +read fstab (or mtab) only when both +.I device +and +.I dir +are specified. +.sp +.in +4 +.B "mount \-o remount,rw /dev/foo /dir" +.in +.sp +After this call all old mount options are replaced and arbitrary stuff from +fstab (or mtab) is ignored, except the loop= option which is internally +generated and maintained by the mount command. +.sp +.in +4 +.B "mount \-o remount,rw /dir" +.in +.sp +After this call, mount reads fstab and merges these options with +the options from the command line (\fB\-o\fR). +If no mountpoint is found in fstab, then a remount with unspecified source is +allowed. +.TP +.B ro +Mount the filesystem read-only. +.TP +.B rw +Mount the filesystem read-write. +.TP +.B sync +All I/O to the filesystem should be done synchronously. In the case of +media with a limited number of write cycles +(e.g.\& some flash drives), \fBsync\fR may cause life-cycle shortening. +.TP +.B user +Allow an ordinary user to mount the filesystem. +The name of the mounting user is written to the mtab file (or to the private +libmount file in /run/mount on systems without a regular mtab) so that this +same user can unmount the filesystem again. +This option implies the options +.BR noexec ", " nosuid ", and " nodev +(unless overridden by subsequent options, as in the option line +.BR user,exec,dev,suid ). +.TP +.B nouser +Forbid an ordinary user to mount the filesystem. +This is the default; it does not imply any other options. +.TP +.B users +Allow any user to mount and to unmount the filesystem, even +when some other ordinary user mounted it. +This option implies the options +.BR noexec ", " nosuid ", and " nodev +(unless overridden by subsequent options, as in the option line +.BR users,exec,dev,suid ). +.TP +.B X-* +All options prefixed with "X-" are interpreted as comments or as userspace +application-specific options. These options are not stored in the user space (e.g. mtab file), +nor sent to the mount.\fItype\fR helpers nor to the +.BR mount (2) +system call. The suggested format is \fBX-\fIappname\fR.\fIoption\fR. +.TP +.B x-* +The same as \fBX-*\fR options, but stored permanently in the user space. It +means the options are also available for umount or another operations. Note +that maintain mount options in user space is tricky, because it's necessary use +libmount based tools and there is no guarantee that the options will be always +available (for example after a move mount operation or in unshared namespace). + +Note that before util-linux v2.30 the x-* options have not been maintained by +libmount and stored in user space (functionality was the same as have X-* now), +but due to growing number of use-cases (in initrd, systemd etc.) the +functionality have been extended to keep existing fstab configurations usable +without a change. +.TP +.BR X-mount.mkdir [ = \fImode\fR ] +Allow to make a target directory (mountpoint). The optional argument +.I mode +specifies the filesystem access mode used for +.BR mkdir (2) +in octal notation. The default mode is 0755. This functionality is supported +only for root users. The option is also supported as x-mount.mkdir, this notation +is deprecated for mount.mkdir since v2.30. + +.SH "FILESYSTEM-SPECIFIC MOUNT OPTIONS" +You should consult the respective man page for the filesystem first. +If you want to know what options the ext4 filesystem supports, then check the +.BR ext4 (5) +man page. +If that doesn't exist, you can also check the corresponding mount page like +.BR mount.cifs (8). +Note that you might have to install the respective userland tools. +.sp +The following options apply only to certain filesystems. +We sort them by filesystem. They all follow the +.B \-o +flag. +.sp +What options are supported depends a bit on the running kernel. +More info may be found in the kernel source subdirectory +.IR Documentation/filesystems . + +.SS "Mount options for adfs" +.TP +\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP +Set the owner and group of the files in the filesystem (default: uid=gid=0). +.TP +\fBownmask=\fP\,\fIvalue\fP and \fBothmask=\fP\,\fIvalue\fP +Set the permission mask for ADFS 'owner' permissions and 'other' permissions, +respectively (default: 0700 and 0077, respectively). +See also +.IR /usr/src/linux/Documentation/filesystems/adfs.txt . + +.SS "Mount options for affs" +.TP +\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP +Set the owner and group of the root of the filesystem (default: uid=gid=0, +but with option +.B uid +or +.B gid +without specified value, the UID and GID of the current process are taken). +.TP +\fBsetuid=\fP\,\fIvalue\fP and \fBsetgid=\fP\,\fIvalue\fP +Set the owner and group of all files. +.TP +.BI mode= value +Set the mode of all files to +.IR value " & 0777" +disregarding the original permissions. +Add search permission to directories that have read permission. +The value is given in octal. +.TP +.B protect +Do not allow any changes to the protection bits on the filesystem. +.TP +.B usemp +Set UID and GID of the root of the filesystem to the UID and GID +of the mount point upon the first sync or umount, and then +clear this option. Strange... +.TP +.B verbose +Print an informational message for each successful mount. +.TP +.BI prefix= string +Prefix used before volume name, when following a link. +.TP +.BI volume= string +Prefix (of length at most 30) used before '/' when following a symbolic link. +.TP +.BI reserved= value +(Default: 2.) Number of unused blocks at the start of the device. +.TP +.BI root= value +Give explicitly the location of the root block. +.TP +.BI bs= value +Give blocksize. Allowed values are 512, 1024, 2048, 4096. +.TP +.BR grpquota | noquota | quota | usrquota +These options are accepted but ignored. +(However, quota utilities may react to such strings in +.IR /etc/fstab .) + +.SS "Mount options for debugfs" +The debugfs filesystem is a pseudo filesystem, traditionally mounted on +.IR /sys/kernel/debug . +.\" or just /debug +.\" present since 2.6.11 +As of kernel version 3.4, debugfs has the following options: +.TP +.BI uid= n ", gid=" n +Set the owner and group of the mountpoint. +.TP +.BI mode= value +Sets the mode of the mountpoint. + +.SS "Mount options for devpts" +The devpts filesystem is a pseudo filesystem, traditionally mounted on +.IR /dev/pts . +In order to acquire a pseudo terminal, a process opens +.IR /dev/ptmx ; +the number of the pseudo terminal is then made available to the process +and the pseudo terminal slave can be accessed as +.IR /dev/pts/ <number>. +.TP +\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP +This sets the owner or the group of newly created PTYs to +the specified values. When nothing is specified, they will +be set to the UID and GID of the creating process. +For example, if there is a tty group with GID 5, then +.B gid=5 +will cause newly created PTYs to belong to the tty group. +.TP +.BI mode= value +Set the mode of newly created PTYs to the specified value. +The default is 0600. +A value of +.B mode=620 +and +.B gid=5 +makes "mesg y" the default on newly created PTYs. +.TP +\fBnewinstance +Create a private instance of devpts filesystem, such that +indices of ptys allocated in this new instance are +independent of indices created in other instances of devpts. + +All mounts of devpts without this +.B newinstance +option share the same set of pty indices (i.e. legacy mode). +Each mount of devpts with the +.B newinstance +option has a private set of pty indices. + +This option is mainly used to support containers in the +linux kernel. It is implemented in linux kernel versions +starting with 2.6.29. Further, this mount option is valid +only if CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the +kernel configuration. + +To use this option effectively, +.I /dev/ptmx +must be a symbolic link to +.I pts/ptmx. +See +.I Documentation/filesystems/devpts.txt +in the linux kernel source tree for details. +.TP +.BI ptmxmode= value + +Set the mode for the new +.I ptmx +device node in the devpts filesystem. + +With the support for multiple instances of devpts (see +.B newinstance +option above), each instance has a private +.I ptmx +node in the root of the devpts filesystem (typically +.IR /dev/pts/ptmx ). + +For compatibility with older versions of the kernel, the +default mode of the new +.I ptmx +node is 0000. +.BI ptmxmode= value +specifies a more useful mode for the +.I ptmx +node and is highly recommended when the +.B newinstance +option is specified. + +This option is only implemented in linux kernel versions +starting with 2.6.29. Further, this option is valid only if +CONFIG_DEVPTS_MULTIPLE_INSTANCES is enabled in the kernel +configuration. + +.SS "Mount options for fat" +(Note: +.I fat +is not a separate filesystem, but a common part of the +.IR msdos , +.I umsdos +and +.I vfat +filesystems.) +.TP +.BR blocksize= { 512 | 1024 | 2048 } +Set blocksize (default 512). This option is obsolete. +.TP +\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP +Set the owner and group of all files. +(Default: the UID and GID of the current process.) +.TP +.BI umask= value +Set the umask (the bitmask of the permissions that are +.B not +present). The default is the umask of the current process. +The value is given in octal. +.TP +.BI dmask= value +Set the umask applied to directories only. +The default is the umask of the current process. +The value is given in octal. +.TP +.BI fmask= value +Set the umask applied to regular files only. +The default is the umask of the current process. +The value is given in octal. +.TP +.BI allow_utime= value +This option controls the permission check of mtime/atime. +.RS +.TP +.B 20 +If current process is in group of file's group ID, you can change timestamp. +.TP +.B 2 +Other users can change timestamp. +.PP +The default is set from `dmask' option. (If the directory is writable, +.BR utime (2) +is also allowed. I.e.\& \s+3~\s0dmask & 022) + +Normally +.BR utime (2) +checks current process is owner of the file, or it has +CAP_FOWNER capability. But FAT filesystem doesn't have UID/GID on disk, so +normal check is too inflexible. With this option you can relax it. +.RE +.TP +.BI check= value +Three different levels of pickiness can be chosen: +.RS +.TP +.BR r [ elaxed ] +Upper and lower case are accepted and equivalent, long name parts are +truncated (e.g.\& +.I verylongname.foobar +becomes +.IR verylong.foo ), +leading and embedded spaces are accepted in each name part (name and extension). +.TP +.BR n [ ormal ] +Like "relaxed", but many special characters (*, ?, <, spaces, etc.) are +rejected. This is the default. +.TP +.BR s [ trict ] +Like "normal", but names that contain long parts or special characters +that are sometimes used on Linux but are not accepted by MS-DOS +(+, =, etc.) are rejected. +.RE +.TP +.BI codepage= value +Sets the codepage for converting to shortname characters on FAT +and VFAT filesystems. By default, codepage 437 is used. +.TP +.BI conv= mode +This option is obsolete and may fail or being ignored. +.TP +.BI cvf_format= module +Forces the driver to use the CVF (Compressed Volume File) module +.RI cvf_ module +instead of auto-detection. If the kernel supports kmod, the +cvf_format=xxx option also controls on-demand CVF module loading. +This option is obsolete. +.TP +.BI cvf_option= option +Option passed to the CVF module. This option is obsolete. +.TP +.B debug +Turn on the +.I debug +flag. A version string and a list of filesystem parameters will be +printed (these data are also printed if the parameters appear to be +inconsistent). +.TP +.B discard +If set, causes discard/TRIM commands to be issued to the block device +when blocks are freed. This is useful for SSD devices and +sparse/thinly-provisioned LUNs. +.TP +.B dos1xfloppy +If set, use a fallback default BIOS Parameter Block configuration, determined +by backing device size. These static parameters match defaults assumed by DOS +1.x for 160 kiB, 180 kiB, 320 kiB, and 360 kiB floppies and floppy images. +.TP +.BR errors= { panic | continue | remount-ro } +Specify FAT behavior on critical errors: panic, continue without doing +anything, or remount the partition in read-only mode (default behavior). +.TP +.BR fat= { 12 | 16 | 32 } +Specify a 12, 16 or 32 bit fat. This overrides +the automatic FAT type detection routine. Use with caution! +.TP +.BI iocharset= value +Character set to use for converting between 8 bit characters +and 16 bit Unicode characters. The default is iso8859-1. +Long filenames are stored on disk in Unicode format. +.TP +.BR nfs= { stale_rw | nostale_ro } +Enable this only if you want to export the FAT filesystem over NFS. + +.BR stale_rw : +This option maintains an index (cache) of directory inodes which is used by the +nfs-related code to improve look-ups. Full file operations (read/write) over +NFS are supported but with cache eviction at NFS server, this could result in +spurious +.B ESTALE +errors. + +.BR nostale_ro : +This option bases the inode number and file handle +on the on-disk location of a file in the FAT directory entry. +This ensures that +.B ESTALE +will not be returned after a file is +evicted from the inode cache. However, it means that operations +such as rename, create and unlink could cause file handles that +previously pointed at one file to point at a different file, +potentially causing data corruption. For this reason, this +option also mounts the filesystem readonly. + +To maintain backward compatibility, '-o nfs' is also accepted, +defaulting to +.BR stale_rw . +.TP +.B tz=UTC +This option disables the conversion of timestamps +between local time (as used by Windows on FAT) and UTC +(which Linux uses internally). This is particularly +useful when mounting devices (like digital cameras) +that are set to UTC in order to avoid the pitfalls of +local time. +.TP +.BI time_offset= minutes +Set offset for conversion of timestamps from local time used by FAT to UTC. +I.e., +.I minutes +will be subtracted from each timestamp to convert it to UTC used +internally by Linux. This is useful when the time zone set in the kernel via +.BR settimeofday (2) +is not the time zone used by the filesystem. Note +that this option still does not provide correct time stamps in all cases in +presence of DST - time stamps in a different DST setting will be off by one +hour. +.TP +.B quiet +Turn on the +.I quiet +flag. Attempts to chown or chmod files do not return errors, +although they fail. Use with caution! +.TP +.B rodir +FAT has the ATTR_RO (read-only) attribute. On Windows, the ATTR_RO of the +directory will just be ignored, and is used only by applications as a flag +(e.g.\& it's set for the customized folder). + +If you want to use ATTR_RO as read-only flag even for the directory, set this +option. +.TP +.B showexec +If set, the execute permission bits of the file will be allowed only if +the extension part of the name is \&.EXE, \&.COM, or \&.BAT. Not set by default. +.TP +.B sys_immutable +If set, ATTR_SYS attribute on FAT is handled as IMMUTABLE flag on Linux. +Not set by default. +.TP +.B flush +If set, the filesystem will try to flush to disk more early than normal. +Not set by default. +.TP +.B usefree +Use the "free clusters" value stored on FSINFO. It'll +be used to determine number of free clusters without +scanning disk. But it's not used by default, because +recent Windows don't update it correctly in some +case. If you are sure the "free clusters" on FSINFO is +correct, by this option you can avoid scanning disk. +.TP +.BR dots ", " nodots ", " dotsOK= [ yes | no ] +Various misguided attempts to force Unix or DOS conventions +onto a FAT filesystem. + +.SS "Mount options for hfs" +.TP +.BI creator= cccc ", type=" cccc +Set the creator/type values as shown by the MacOS finder +used for creating new files. Default values: '????'. +.TP +.BI uid= n ", gid=" n +Set the owner and group of all files. +(Default: the UID and GID of the current process.) +.TP +.BI dir_umask= n ", file_umask=" n ", umask=" n +Set the umask used for all directories, all regular files, or all +files and directories. Defaults to the umask of the current process. +.TP +.BI session= n +Select the CDROM session to mount. +Defaults to leaving that decision to the CDROM driver. +This option will fail with anything but a CDROM as underlying device. +.TP +.BI part= n +Select partition number n from the device. +Only makes sense for CDROMs. +Defaults to not parsing the partition table at all. +.TP +.B quiet +Don't complain about invalid mount options. + +.SS "Mount options for hpfs" +.TP +\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP +Set the owner and group of all files. (Default: the UID and GID +of the current process.) +.TP +.BI umask= value +Set the umask (the bitmask of the permissions that are +.B not +present). The default is the umask of the current process. +The value is given in octal. +.TP +.BR case= { lower | asis } +Convert all files names to lower case, or leave them. +(Default: +.BR case=lower .) +.TP +.BI conv= mode +This option is obsolete and may fail or being ignored. +.TP +.B nocheck +Do not abort mounting when certain consistency checks fail. + +.SS "Mount options for iso9660" +ISO 9660 is a standard describing a filesystem structure to be used +on CD-ROMs. (This filesystem type is also seen on some DVDs. See also the +.I udf +filesystem.) + +Normal +.I iso9660 +filenames appear in an 8.3 format (i.e., DOS-like restrictions on filename +length), and in addition all characters are in upper case. Also there is +no field for file ownership, protection, number of links, provision for +block/character devices, etc. + +Rock Ridge is an extension to iso9660 that provides all of these UNIX-like +features. Basically there are extensions to each directory record that +supply all of the additional information, and when Rock Ridge is in use, +the filesystem is indistinguishable from a normal UNIX filesystem (except +that it is read-only, of course). +.TP +.B norock +Disable the use of Rock Ridge extensions, even if available. Cf.\& +.BR map . +.TP +.B nojoliet +Disable the use of Microsoft Joliet extensions, even if available. Cf.\& +.BR map . +.TP +.BR check= { r [ elaxed ]| s [ trict ]} +With +.BR check=relaxed , +a filename is first converted to lower case before doing the lookup. +This is probably only meaningful together with +.B norock +and +.BR map=normal . +(Default: +.BR check=strict .) +.TP +\fBuid=\fP\,\fIvalue\fP and \fBgid=\fP\,\fIvalue\fP +Give all files in the filesystem the indicated user or group id, +possibly overriding the information found in the Rock Ridge extensions. +(Default: +.BR uid=0,gid=0 .) +.TP +.BR map= { n [ ormal ]| o [ ff ]| a [ corn ]} +For non-Rock Ridge volumes, normal name translation maps upper +to lower case ASCII, drops a trailing `;1', and converts `;' to `.'. +With +.B map=off +no name translation is done. See +.BR norock . +(Default: +.BR map=normal .) +.B map=acorn +is like +.B map=normal +but also apply Acorn extensions if present. +.TP +.BI mode= value +For non-Rock Ridge volumes, give all files the indicated mode. +(Default: read and execute permission for everybody.) +Octal mode values require a leading 0. +.TP +.B unhide +Also show hidden and associated files. +(If the ordinary files and the associated or hidden files have +the same filenames, this may make the ordinary files inaccessible.) +.TP +.BR block= { 512 | 1024 | 2048 } +Set the block size to the indicated value. +(Default: +.BR block=1024 .) +.TP +.BI conv= mode +This option is obsolete and may fail or being ignored. +.TP +.B cruft +If the high byte of the file length contains other garbage, +set this mount option to ignore the high order bits of the file length. +This implies that a file cannot be larger than 16\ MB. +.TP +.BI session= x +Select number of session on multisession CD. +.TP +.BI sbsector= xxx +Session begins from sector xxx. +.LP +The following options are the same as for vfat and specifying them only makes +sense when using discs encoded using Microsoft's Joliet extensions. +.TP +.BI iocharset= value +Character set to use for converting 16 bit Unicode characters on CD +to 8 bit characters. The default is iso8859-1. +.TP +.B utf8 +Convert 16 bit Unicode characters on CD to UTF-8. + +.SS "Mount options for jfs" +.TP +.BI iocharset= name +Character set to use for converting from Unicode to ASCII. The default is +to do no conversion. Use +.B iocharset=utf8 +for UTF8 translations. This requires CONFIG_NLS_UTF8 to be set in +the kernel +.I ".config" +file. +.TP +.BI resize= value +Resize the volume to +.I value +blocks. JFS only supports growing a volume, not shrinking it. This option +is only valid during a remount, when the volume is mounted read-write. The +.B resize +keyword with no value will grow the volume to the full size of the partition. +.TP +.B nointegrity +Do not write to the journal. The primary use of this option is to allow +for higher performance when restoring a volume from backup media. The +integrity of the volume is not guaranteed if the system abnormally ends. +.TP +.B integrity +Default. Commit metadata changes to the journal. Use this option to remount +a volume where the +.B nointegrity +option was previously specified in order to restore normal behavior. +.TP +.BR errors= { continue | remount-ro | panic } +Define the behavior when an error is encountered. +(Either ignore errors and just mark the filesystem erroneous and continue, +or remount the filesystem read-only, or panic and halt the system.) +.TP +.BR noquota | quota | usrquota | grpquota +These options are accepted but ignored. + +.SS "Mount options for msdos" +See mount options for fat. +If the +.I msdos +filesystem detects an inconsistency, it reports an error and sets the file +system read-only. The filesystem can be made writable again by remounting +it. + +.SS "Mount options for ncpfs" +Just like +.IR nfs ", the " ncpfs +implementation expects a binary argument (a +.IR "struct ncp_mount_data" ) +to the mount system call. This argument is constructed by +.BR ncpmount (8) +and the current version of +.B mount +(2.12) does not know anything about ncpfs. + +.SS "Mount options for ntfs" +.TP +.BI iocharset= name +Character set to use when returning file names. +Unlike VFAT, NTFS suppresses names that contain +nonconvertible characters. Deprecated. +.TP +.BI nls= name +New name for the option earlier called +.IR iocharset . +.TP +.B utf8 +Use UTF-8 for converting file names. +.TP +.BR uni_xlate= { 0 | 1 | 2 } +For 0 (or `no' or `false'), do not use escape sequences +for unknown Unicode characters. +For 1 (or `yes' or `true') or 2, use vfat-style 4-byte escape sequences +starting with ":". Here 2 give a little-endian encoding +and 1 a byteswapped bigendian encoding. +.TP +.B posix=[0|1] +If enabled (posix=1), the filesystem distinguishes between +upper and lower case. The 8.3 alias names are presented as +hard links instead of being suppressed. This option is obsolete. +.TP +\fBuid=\fP\,\fIvalue\fP, \fBgid=\fP\,\fIvalue\fP and \fBumask=\fP\,\fIvalue\fP +Set the file permission on the filesystem. +The umask value is given in octal. +By default, the files are owned by root and not readable by somebody else. + +.SS "Mount options for overlay" +Since Linux 3.18 the overlay pseudo filesystem implements a union mount for +other filesystems. + +An overlay filesystem combines two filesystems - an \fBupper\fR filesystem and +a \fBlower\fR filesystem. When a name exists in both filesystems, the object +in the upper filesystem is visible while the object in the lower filesystem is +either hidden or, in the case of directories, merged with the upper object. + +The lower filesystem can be any filesystem supported by Linux and does not need +to be writable. The lower filesystem can even be another overlayfs. The upper +filesystem will normally be writable and if it is it must support the creation +of trusted.* extended attributes, and must provide a valid d_type in readdir +responses, so NFS is not suitable. + +A read-only overlay of two read-only filesystems may use any filesystem type. +The options \fBlowerdir\fR and \fBupperdir\fR are combined into a merged +directory by using: + +.RS +.br +.nf +.B "mount \-t overlay overlay \e" +.B " \-olowerdir=/lower,upperdir=/upper,workdir=/work /merged" +.fi +.br +.RE + +.TP +.BI lowerdir= directory +Any filesystem, does not need to be on a writable filesystem. +.TP +.BI upperdir= directory +The upperdir is normally on a writable filesystem. +.TP +.BI workdir= directory +The workdir needs to be an empty directory on the same filesystem as upperdir. + +.SS "Mount options for reiserfs" +Reiserfs is a journaling filesystem. +.TP +.B conv +Instructs version 3.6 reiserfs software to mount a version 3.5 filesystem, +using the 3.6 format for newly created objects. This filesystem will no +longer be compatible with reiserfs 3.5 tools. +.TP +.BR hash= { rupasov | tea | r5 | detect } +Choose which hash function reiserfs will use to find files within directories. +.RS +.TP +.B rupasov +A hash invented by Yury Yu.\& Rupasov. It is fast and preserves locality, +mapping lexicographically close file names to close hash values. +This option should not be used, as it causes a high probability of hash +collisions. +.TP +.B tea +A Davis-Meyer function implemented by Jeremy Fitzhardinge. +It uses hash permuting bits in the name. It gets high randomness +and, therefore, low probability of hash collisions at some CPU cost. +This may be used if EHASHCOLLISION errors are experienced with the r5 hash. +.TP +.B r5 +A modified version of the rupasov hash. It is used by default and is +the best choice unless the filesystem has huge directories and +unusual file-name patterns. +.TP +.B detect +Instructs +.I mount +to detect which hash function is in use by examining +the filesystem being mounted, and to write this information into +the reiserfs superblock. This is only useful on the first mount of +an old format filesystem. +.RE +.TP +.B hashed_relocation +Tunes the block allocator. This may provide performance improvements +in some situations. +.TP +.B no_unhashed_relocation +Tunes the block allocator. This may provide performance improvements +in some situations. +.TP +.B noborder +Disable the border allocator algorithm invented by Yury Yu.\& Rupasov. +This may provide performance improvements in some situations. +.TP +.B nolog +Disable journaling. This will provide slight performance improvements in +some situations at the cost of losing reiserfs's fast recovery from crashes. +Even with this option turned on, reiserfs still performs all journaling +operations, save for actual writes into its journaling area. Implementation +of +.I nolog +is a work in progress. +.TP +.B notail +By default, reiserfs stores small files and `file tails' directly into its +tree. This confuses some utilities such as +.BR LILO (8). +This option is used to disable packing of files into the tree. +.TP +.B replayonly +Replay the transactions which are in the journal, but do not actually +mount the filesystem. Mainly used by +.IR reiserfsck . +.TP +.BI resize= number +A remount option which permits online expansion of reiserfs partitions. +Instructs reiserfs to assume that the device has +.I number +blocks. +This option is designed for use with devices which are under logical +volume management (LVM). +There is a special +.I resizer +utility which can be obtained from +.IR ftp://ftp.namesys.com/pub/reiserfsprogs . +.TP +.B user_xattr +Enable Extended User Attributes. See the +.BR attr (5) +manual page. +.TP +.B acl +Enable POSIX Access Control Lists. See the +.BR acl (5) +manual page. +.TP +.BR barrier=none " / " barrier=flush " +This disables / enables the use of write barriers in the journaling code. +barrier=none disables, barrier=flush enables (default). This also requires an +IO stack which can support barriers, and if reiserfs gets an error on a barrier +write, it will disable barriers again with a warning. Write barriers enforce +proper on-disk ordering of journal commits, making volatile disk write caches +safe to use, at some performance penalty. If your disks are battery-backed in +one way or another, disabling barriers may safely improve performance. + +.SS "Mount options for ubifs" +UBIFS is a flash filesystem which works on top of UBI volumes. Note that +\fBatime\fR is not supported and is always turned off. +.TP +The device name may be specified as +.RS +.B ubiX_Y +UBI device number +.BR X , +volume number +.B Y +.TP +.B ubiY +UBI device number +.BR 0 , +volume number +.B Y +.TP +.B ubiX:NAME +UBI device number +.BR X , +volume with name +.B NAME +.TP +.B ubi:NAME +UBI device number +.BR 0 , +volume with name +.B NAME +.RE +Alternative +.B ! +separator may be used instead of +.BR : . +.TP +The following mount options are available: +.TP +.B bulk_read +Enable bulk-read. VFS read-ahead is disabled because it slows down the file +system. Bulk-Read is an internal optimization. Some flashes may read faster if +the data are read at one go, rather than at several read requests. For +example, OneNAND can do "read-while-load" if it reads more than one NAND page. +.TP +.B no_bulk_read +Do not bulk-read. This is the default. +.TP +.B chk_data_crc +Check data CRC-32 checksums. This is the default. +.TP +.BR no_chk_data_crc . +Do not check data CRC-32 checksums. With this option, the filesystem does not +check CRC-32 checksum for data, but it does check it for the internal indexing +information. This option only affects reading, not writing. CRC-32 is always +calculated when writing the data. +.TP +.BR compr= { none | lzo | zlib } +Select the default compressor which is used when new files are written. It is +still possible to read compressed files if mounted with the +.B none +option. + +.SS "Mount options for udf" +UDF is the "Universal Disk Format" filesystem defined by OSTA, the Optical +Storage Technology Association, and is often used for DVD-ROM, frequently +in the form of a hybrid UDF/ISO-9660 filesystem. It is, however, +perfectly usable by itself on disk drives, flash drives and other block devices. +See also +.IR iso9660 . +.TP +.B uid= +Make all files in the filesystem belong to the given user. +uid=forget can be specified independently of (or usually in +addition to) uid=<user> and results in UDF +not storing uids to the media. In fact the recorded uid +is the 32-bit overflow uid -1 as defined by the UDF standard. +The value is given as either <user> which is a valid user name or the corresponding +decimal user id, or the special string "forget". +.TP +.B gid= +Make all files in the filesystem belong to the given group. +gid=forget can be specified independently of (or usually in +addition to) gid=<group> and results in UDF +not storing gids to the media. In fact the recorded gid +is the 32-bit overflow gid -1 as defined by the UDF standard. +The value is given as either <group> which is a valid group name or the corresponding +decimal group id, or the special string "forget". +.TP +.B umask= +Mask out the given permissions from all inodes read from the filesystem. +The value is given in octal. +.TP +.B mode= +If mode= is set the permissions of all non-directory inodes read from the +filesystem will be set to the given mode. The value is given in octal. +.TP +.B dmode= +If dmode= is set the permissions of all directory inodes read from the +filesystem will be set to the given dmode. The value is given in octal. +.TP +.B bs= +Set the block size. Default value prior to kernel version 2.6.30 was +2048. Since 2.6.30 and prior to 4.11 it was logical device block size with +fallback to 2048. Since 4.11 it is logical block size with fallback to +any valid block size between logical device block size and 4096. + +For other details see the \fBmkudffs\fP(8) 2.0+ manpage, sections +\fBCOMPATIBILITY\fP and \fBBLOCK SIZE\fP. +.TP +.B unhide +Show otherwise hidden files. +.TP +.B undelete +Show deleted files in lists. +.TP +.B adinicb +Embed data in the inode. (default) +.TP +.B noadinicb +Don't embed data in the inode. +.TP +.B shortad +Use short UDF address descriptors. +.TP +.B longad +Use long UDF address descriptors. (default) +.TP +.B nostrict +Unset strict conformance. +.TP +.B iocharset= +Set the NLS character set. This requires kernel compiled with CONFIG_UDF_NLS option. +.TP +.B utf8 +Set the UTF-8 character set. +.SS Mount options for debugging and disaster recovery +.TP +.B novrs +Ignore the Volume Recognition Sequence and attempt to mount anyway. +.TP +.B session= +Select the session number for multi-session recorded optical media. (default= last session) +.TP +.B anchor= +Override standard anchor location. (default= 256) +.TP +.B lastblock= +Set the last block of the filesystem. +.SS Unused historical mount options that may be encountered and should be removed +.TP +.B uid=ignore +Ignored, use uid=<user> instead. +.TP +.B gid=ignore +Ignored, use gid=<group> instead. +.TP +.B volume= +Unimplemented and ignored. +.TP +.B partition= +Unimplemented and ignored. +.TP +.B fileset= +Unimplemented and ignored. +.TP +.B rootdir= +Unimplemented and ignored. + +.SS "Mount options for ufs" +.TP +.BI ufstype= value +UFS is a filesystem widely used in different operating systems. +The problem are differences among implementations. Features of some +implementations are undocumented, so its hard to recognize the +type of ufs automatically. +That's why the user must specify the type of ufs by mount option. +Possible values are: +.RS +.TP +.B old +Old format of ufs, this is the default, read only. +(Don't forget to give the \-r option.) +.TP +.B 44bsd +For filesystems created by a BSD-like system (NetBSD, FreeBSD, OpenBSD). +.TP +.B ufs2 +Used in FreeBSD 5.x supported as read-write. +.TP +.B 5xbsd +Synonym for ufs2. +.TP +.B sun +For filesystems created by SunOS or Solaris on Sparc. +.TP +.B sunx86 +For filesystems created by Solaris on x86. +.TP +.B hp +For filesystems created by HP-UX, read-only. +.TP +.B nextstep +For filesystems created by NeXTStep (on NeXT station) (currently read only). +.TP +.B nextstep-cd +For NextStep CDROMs (block_size == 2048), read-only. +.TP +.B openstep +For filesystems created by OpenStep (currently read only). +The same filesystem type is also used by Mac OS X. +.RE + +.TP +.BI onerror= value +Set behavior on error: +.RS +.TP +.B panic +If an error is encountered, cause a kernel panic. +.TP +.RB [ lock | umount | repair ] +These mount options don't do anything at present; +when an error is encountered only a console message is printed. +.RE + +.SS "Mount options for umsdos" +See mount options for msdos. +The +.B dotsOK +option is explicitly killed by +.IR umsdos . + +.SS "Mount options for vfat" +First of all, the mount options for +.I fat +are recognized. +The +.B dotsOK +option is explicitly killed by +.IR vfat . +Furthermore, there are +.TP +.B uni_xlate +Translate unhandled Unicode characters to special escaped sequences. +This lets you backup and restore filenames that are created with any +Unicode characters. Without this option, a '?' is used when no +translation is possible. The escape character is ':' because it is +otherwise invalid on the vfat filesystem. The escape sequence +that gets used, where u is the Unicode character, +is: ':', (u & 0x3f), ((u>>6) & 0x3f), (u>>12). +.TP +.B posix +Allow two files with names that only differ in case. +This option is obsolete. +.TP +.B nonumtail +First try to make a short name without sequence number, +before trying +.IR name\s+3~\s0num.ext . +.TP +.B utf8 +UTF8 is the filesystem safe 8-bit encoding of Unicode that is used by the +console. It can be enabled for the filesystem with this option or disabled +with utf8=0, utf8=no or utf8=false. If `uni_xlate' gets set, UTF8 gets +disabled. +.TP +.BI shortname= mode +Defines the behavior for creation and display of filenames which fit into +8.3 characters. If a long name for a file exists, it will always be the +preferred one for display. There are four \fImode\fRs: +.RS +.TP +.B lower +Force the short name to lower case upon display; store a long name when +the short name is not all upper case. +.TP +.B win95 +Force the short name to upper case upon display; store a long name when +the short name is not all upper case. +.TP +.B winnt +Display the short name as is; store a long name when the short name is +not all lower case or all upper case. +.TP +.B mixed +Display the short name as is; store a long name when the short name is not +all upper case. This mode is the default since Linux 2.6.32. +.RE + +.SS "Mount options for usbfs" +.TP +\fBdevuid=\fP\,\fIuid\fP and \fBdevgid=\fP\,\fIgid\fP and \fBdevmode=\fP\,\fImode\fP +Set the owner and group and mode of the device files in the usbfs filesystem +(default: uid=gid=0, mode=0644). The mode is given in octal. +.TP +\fBbusuid=\fP\,\fIuid\fP and \fBbusgid=\fP\,\fIgid\fP and \fBbusmode=\fP\,\fImode\fP +Set the owner and group and mode of the bus directories in the usbfs +filesystem (default: uid=gid=0, mode=0555). The mode is given in octal. +.TP +\fBlistuid=\fP\,\fIuid\fP and \fBlistgid=\fP\,\fIgid\fP and \fBlistmode=\fP\,\fImode\fP +Set the owner and group and mode of the file +.I devices +(default: uid=gid=0, mode=0444). The mode is given in octal. + +.SH "THE LOOP DEVICE" +One further possible type is a mount via the loop device. For example, +the command +.RS +.sp +.B "mount /tmp/disk.img /mnt \-t vfat \-o loop=/dev/loop3" +.sp +.RE +will set up the loop device +.I /dev/loop3 +to correspond to the file +.IR /tmp/disk.img , +and then mount this device on +.IR /mnt . + +If no explicit loop device is mentioned +(but just an option `\fB\-o loop\fP' is given), then +.B mount +will try to find some unused loop device and use that, for example +.RS +.sp +.B "mount /tmp/disk.img /mnt \-o loop" +.sp +.RE +The mount command +.B automatically +creates a loop device from a regular file if a filesystem type is +not specified or the filesystem is known for libblkid, for example: +.RS +.sp +.B "mount /tmp/disk.img /mnt" +.sp +.B "mount \-t ext4 /tmp/disk.img /mnt" +.sp +.RE +This type of mount knows about three options, namely +.BR loop ", " offset " and " sizelimit , +that are really options to +.BR \%losetup (8). +(These options can be used in addition to those specific +to the filesystem type.) + +Since Linux 2.6.25 auto-destruction of loop devices is supported, +meaning that any loop device allocated by +.B mount +will be freed by +.B umount +independently of +.IR /etc/mtab . + +You can also free a loop device by hand, using +.BR "losetup \-d " or " umount \-d" . + +Since util-linux v2.29 mount command re-uses the loop device rather than +initialize a new device if the same backing file is already used for some loop +device with the same offset and sizelimit. This is necessary to avoid +a filesystem corruption. + +.SH RETURN CODES +.B mount +has the following return codes (the bits can be ORed): +.TP +.B 0 +success +.TP +.B 1 +incorrect invocation or permissions +.TP +.B 2 +system error (out of memory, cannot fork, no more loop devices) +.TP +.B 4 +internal +.B mount +bug +.TP +.B 8 +user interrupt +.TP +.B 16 +problems writing or locking /etc/mtab +.TP +.B 32 +mount failure +.TP +.B 64 +some mount succeeded +.RE + +The command \fBmount \-a\fR returns 0 (all succeeded), 32 (all failed), or 64 (some +failed, some succeeded). + +.SH "EXTERNAL HELPERS" +The syntax of external mount helpers is: +.sp +.in +4 +.BI /sbin/mount. suffix +.I spec dir +.RB [ \-sfnv ] +.RB [ \-N +.IR namespace ] +.RB [ \-o +.IR options ] +.RB [ \-t +.IR type \fB. subtype ] +.in +.sp +where the \fIsuffix\fR is the filesystem type and the \fB\-sfnvoN\fR options have +the same meaning as the normal mount options. The \fB\-t\fR option is used for +filesystems with subtypes support (for example +.BR "/sbin/mount.fuse \-t fuse.sshfs" ). + +The command \fBmount\fR does not pass the mount options +.BR unbindable , +.BR runbindable , +.BR private , +.BR rprivate , +.BR slave , +.BR rslave , +.BR shared , +.BR rshared , +.BR auto , +.BR noauto , +.BR comment , +.BR x-* , +.BR loop , +.B offset +and +.B sizelimit +to the mount.<suffix> helpers. All other options are used in a +comma-separated list as argument to the \fB\-o\fR option. + +.SH FILES +See also "\fBThe files /etc/fstab, /etc/mtab and /proc/mounts\fR" section above. +.TP 18n +.I /etc/fstab +filesystem table +.TP +.I /run/mount +libmount private runtime directory +.TP +.I /etc/mtab +table of mounted filesystems or symlink to /proc/mounts +.TP +.I /etc/mtab\s+3~\s0 +lock file (unused on systems with mtab symlink) +.TP +.I /etc/mtab.tmp +temporary file (unused on systems with mtab symlink) +.TP +.I /etc/filesystems +a list of filesystem types to try +.SH ENVIRONMENT +.IP LIBMOUNT_FSTAB=<path> +overrides the default location of the fstab file (ignored for suid) +.IP LIBMOUNT_MTAB=<path> +overrides the default location of the mtab file (ignored for suid) +.IP LIBMOUNT_DEBUG=all +enables libmount debug output +.IP LIBBLKID_DEBUG=all +enables libblkid debug output +.IP LOOPDEV_DEBUG=all +enables loop device setup debug output +.SH "SEE ALSO" +.na +.BR mount (2), +.BR umount (2), +.BR umount (8), +.BR fstab (5), +.BR nfs (5), +.BR xfs (5), +.BR e2label (8), +.BR findmnt (8), +.BR losetup (8), +.BR mke2fs (8), +.BR mountd (8), +.BR nfsd (8), +.BR swapon (8), +.BR tune2fs (8), +.BR xfs_admin (8) +.ad +.SH BUGS +It is possible for a corrupted filesystem to cause a crash. +.PP +Some Linux filesystems don't support +.BR "\-o sync " nor " \-o dirsync" +(the ext2, ext3, ext4, fat and vfat filesystems +.I do +support synchronous updates (a la BSD) when mounted with the +.B sync +option). +.PP +The +.B "\-o remount" +may not be able to change mount parameters (all +.IR ext2fs -specific +parameters, except +.BR sb , +are changeable with a remount, for example, but you can't change +.B gid +or +.B umask +for the +.IR fatfs ). +.PP +It is possible that the files +.I /etc/mtab +and +.I /proc/mounts +don't match on systems with a regular mtab file. The first file is based only on +the mount command options, but the content of the second file also depends on +the kernel and others settings (e.g.\& on a remote NFS server -- in certain cases +the mount command may report unreliable information about an NFS mount point +and the /proc/mounts file usually contains more reliable information.) This is +another reason to replace the mtab file with a symlink to the +.I /proc/mounts +file. +.PP +Checking files on NFS filesystems referenced by file descriptors (i.e.\& the +.B fcntl +and +.B ioctl +families of functions) may lead to inconsistent results due to the lack of +a consistency check in the kernel even if noac is used. +.PP +The +.B loop +option with the +.B offset +or +.B sizelimit +options used may fail when using older kernels if the +.B mount +command can't confirm that the size of the block device has been configured +as requested. This situation can be worked around by using +the +.B losetup +command manually before calling +.B mount +with the configured loop device. +.SH HISTORY +A +.B mount +command existed in Version 5 AT&T UNIX. +.SH AUTHORS +.nf +Karel Zak <kzak@redhat.com> +.fi +.SH AVAILABILITY +The mount command is part of the util-linux package and is available from +https://www.kernel.org/pub/linux/utils/util-linux/. |