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.\" Copyright (c) 1980, 1989, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\" @(#)mount.8 8.8 (Berkeley) 6/16/94
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.\" $FreeBSD: src/sbin/mount/mount.8,v 1.82.2.5.4.1 2010/02/10 00:26:20 kensmith Exp $
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.Nd mount file systems
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.Op Fl t Cm ufs | Ar external_type
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.Op Fl t Cm ufs | Ar external_type
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system call to prepare and graft a
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device or the remote node (rhost:path) on to the file system tree at the point
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are not provided, the appropriate information is taken from the
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The system maintains a list of currently mounted file systems.
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If no arguments are given to
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The options are as follows:
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.Bl -tag -width indent
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All the file systems described in
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Exceptions are those marked as
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option was specified),
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flag (see below), or if they are already mounted (except the
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root file system which is always remounted to preserve
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traditional single user mode behavior).
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Causes everything to be done except for the actual system call.
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This option is useful in conjunction with the
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command is trying to do.
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Forces the revocation of write access when trying to downgrade
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a file system mount status from read-write to read-only.
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forces the R/W mount of an unclean file system (dangerous; use with
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When used in conjunction with the
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option, also mount those file systems which are marked as
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Options are specified with a
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flag followed by a comma separated string of options.
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In case of conflicting options being specified, the rightmost option
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The following options are available:
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.Bl -tag -width indent
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Enable Access Control Lists, or ACLS, which can be customized via the
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to the file system should be done asynchronously.
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flag to set, since it does not guarantee that the file system structure
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on the disk will remain consistent.
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flag should be used sparingly, and only when some data recovery
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mechanism is present.
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flag, this is the same as specifying the options currently in effect for
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the mounted file system.
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forces the revocation of write access when trying to downgrade
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a file system mount status from read-write to read-only.
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forces the R/W mount of an unclean file system (dangerous; use with caution).
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flag, this is the same as specifying all the options listed in the
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file for the file system.
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This file system should be skipped when
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.It Cm mountprog Ns = Ns Aq Ar program
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to use the specified program to mount the file system, instead of calling
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directly. For example:
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mount -t foofs -o mountprog=/mydir/fooprog /dev/acd0 /mnt
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Enable multi-label Mandatory Access Control, or MAC, on the specified file
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If the file system supports multilabel operation, individual labels will
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be maintained for each object in the file system, rather than using a
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single label for all objects.
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An alternative to the
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for more information, which cause the multilabel mount flag to be set
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automatically at mount-time.
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Metadata I/O should be done synchronously, while data I/O should be done
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Do not update the file access time when reading from a file.
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is useful on file systems where there are large numbers of files and
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performance is more critical than updating the file access time (which is
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rarely ever important).
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This option is currently only supported on local file systems.
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This file system should be skipped when
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Disable read clustering.
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Disable write clustering.
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Do not allow execution of any binaries on the mounted file system.
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This option is useful for a server that has file systems containing
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binaries for architectures other than its own.
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Note: This option was not designed as a security feature and no
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guarantee is made that it will prevent malicious code execution; for
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example, it is still possible to execute scripts which reside on a
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Do not allow set-user-identifier or set-group-identifier bits to take effect.
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Note: this option is worthless if a public available suid or sgid
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is installed on your system.
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It is set automatically when the user does not have super-user privileges.
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Do not follow symlinks
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on the mounted file system.
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mount the file system read-only (even the super-user may not write it).
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This option allows a snapshot of the specified file system to be taken.
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flag is required with this option.
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Note that snapshot files must be created in the file system that is being
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You may create up to 20 snapshots per file system.
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Active snapshots are recorded in the superblock, so they persist across unmount
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and remount operations and across system reboots.
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When you are done with a snapshot, it can be removed with the
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Snapshots may be removed in any order, however you may not get back all the
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space contained in the snapshot as another snapshot may claim some of the blocks
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that it is releasing.
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Note that the schg flag is set on snapshots to ensure that not even the root
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user can write to them.
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The unlink command makes an exception for snapshot files in that it allows them
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to be removed even though they have the schg flag set, so it is not necessary to
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clear the schg flag before removing a snapshot file.
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Once you have taken a snapshot, there are three interesting things that you can
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on the snapshot file.
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Assuming that the file system was clean when it was mounted, you should always
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get a clean (and unchanging) result from running fsck on the snapshot.
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This is essentially what the background fsck process does.
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You will get a dump that is consistent with the file system as of the timestamp
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Mount the snapshot as a frozen image of the file system.
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To mount the snapshot
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.Pa /var/snapshot/snap1 :
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mdconfig -a -t vnode -f /var/snapshot/snap1 -u 4
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mount -r /dev/md4 /mnt
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You can now cruise around your frozen
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Everything will be in the same state that it was at the time the snapshot was
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The one exception is that any earlier snapshots will appear as zero length
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When you are done with the mounted snapshot:
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Further details can be found in the file at
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.Pa /usr/src/sys/ufs/ffs/README.snapshot .
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A directory on the mounted file system will respond to the SUID bit
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being set, by setting the owner of any new files to be the same
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as the owner of the directory.
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New directories will inherit the bit from their parents.
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Execute bits are removed from
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the file, and it will not be given to root.
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This feature is designed for use on fileservers serving PC users via
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ftp, SAMBA, or netatalk.
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It provides security holes for shell users and as
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such should not be used on shell machines, especially on home directories.
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This option requires the SUIDDIR
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option in the kernel to work.
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Only UFS file systems support this option.
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for more information.
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to the file system should be done synchronously.
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indicate that the status of an already mounted file system should be changed.
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Causes the namespace at the mount point to appear as the union
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of the mounted file system root and the existing directory.
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Lookups will be done in the mounted file system first.
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If those operations fail due to a non-existent file the underlying
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directory is then accessed.
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All creates are done in the mounted file system.
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Any additional options specific to a file system type that is not
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one of the internally known types (see the
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option) may be passed as a comma separated list; these options are
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distinguished by a leading
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Options that take a value are specified using the syntax -option=value.
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.Bd -literal -offset indent
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mount -t cd9660 -o -e /dev/cd0 /cdrom
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to execute the equivalent of:
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.Bd -literal -offset indent
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/sbin/mount_cd9660 -e /dev/cd0 /cdrom
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Additional options specific to file system types
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which are not internally known
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(see the description of the
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may be described in the manual pages for the associated
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.Pa /sbin/mount_ Ns Sy XXX
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Print mount information in
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The file system is to be mounted read-only.
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Mount the file system read-only (even the super-user may not write it).
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.It Fl t Cm ufs | Ar external_type
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The argument following the
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is used to indicate the file system type.
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to indicate that the actions should only be taken on
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file systems of the specified type.
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More than one type may be specified in a comma separated list.
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The list of file system types can be prefixed with
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to specify the file system types for which action should
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.Bd -literal -offset indent
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mount -a -t nonfs,nullfs
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mounts all file systems except those of type
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The default behavior of
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option directly to the
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However, for the following file system types:
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directly and will instead attempt to execute a program in
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.Pa /sbin/mount_ Ns Sy XXX
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is replaced by the file system type name.
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For example, nfs file systems are mounted by the program
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.Pa /sbin/mount_nfs .
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Most file systems will be dynamically loaded by the kernel
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if not already present, and if the kernel module is available.
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flag indicates that the status of an already mounted file
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system should be changed.
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Any of the options discussed above (the
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also a file system can be changed from read-only to read-write
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An attempt to change from read-write to read-only will fail if any
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files on the file system are currently open for writing unless the
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flag is also specified.
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The set of options is determined by applying the options specified
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and finally applying the
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The file system object is to be read and write.
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.Bl -tag -width ".Ev PATH_FSTAB"
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If the environment variable
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is set, all operations are performed against the specified file.
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will not be honored if the process environment or memory address space is
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for more information.)
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.Bl -tag -width /etc/fstab -compact
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Various, most of them are self-explanatory.
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.Dl XXXXX file system is not available
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The kernel does not support the respective file system type.
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support for a particular file system might be provided either on a static
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(kernel compile-time), or dynamic basis (loaded as a kernel module by
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.Xr mount_msdosfs 8 ,
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.Xr mount_portalfs 8 ,
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.Xr mount_unionfs 8 ,
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the permissions on the original mount point determine if
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is accessible from the mounted file system.
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The minimum permissions for
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the mount point for traversal across the mount point in both
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directions to be possible for all users is 0111 (execute for all).
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is preferred over the use of the file system specific
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signal (that causes an update of the export list)
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only when the file system is mounted via
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It is possible for a corrupted file system to cause a crash.
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mount/mount.8
