fbbd9655e5
Renumber cluase 4 to 3, per what everybody else did when BSD granted them permission to remove clause 3. My insistance on keeping the same numbering for legal reasons is too pedantic, so give up on that point. Submitted by: Jan Schaumann <jschauma@stevens.edu> Pull Request: https://github.com/freebsd/freebsd/pull/96
379 lines
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379 lines
10 KiB
Groff
.\" Copyright (c) 1980, 1989, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)mount.2 8.3 (Berkeley) 5/24/95
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.\" $FreeBSD$
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.\"
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.Dd April 13, 2015
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.Dt MOUNT 2
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.Os
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.Sh NAME
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.Nm mount ,
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.Nm nmount ,
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.Nm unmount
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.Nd mount or dismount a file system
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/mount.h
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.Ft int
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.Fn mount "const char *type" "const char *dir" "int flags" "void *data"
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.Ft int
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.Fn unmount "const char *dir" "int flags"
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.In sys/uio.h
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.Ft int
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.Fn nmount "struct iovec *iov" "u_int niov" "int flags"
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.Sh DESCRIPTION
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The
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.Fn mount
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system call grafts
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a file system object onto the system file tree
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at the point
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.Fa dir .
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The argument
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.Fa data
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describes the file system object to be mounted.
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The argument
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.Fa type
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tells the kernel how to interpret
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.Fa data
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(See
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.Fa type
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below).
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The contents of the file system
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become available through the new mount point
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.Fa dir .
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Any files in
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.Fa dir
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at the time
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of a successful mount are swept under the carpet so to speak, and
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are unavailable until the file system is unmounted.
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.Pp
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The
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.Fn nmount
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system call behaves similarly to
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.Fn mount ,
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except that the mount options (file system type name, device to mount,
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mount-point name, etc.) are passed as an array of name-value pairs
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in the array
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.Fa iov ,
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containing
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.Fa niov
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elements.
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The following options are required by all file systems:
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.Bl -column fstype -offset indent
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.It
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.Li fstype Ta file system type name (e.g., Dq Li procfs )
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.It
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.Li fspath Ta mount point pathname (e.g., Dq Li /proc )
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.El
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.Pp
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Depending on the file system type, other options may be
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recognized or required;
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for example, most disk-based file systems require a
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.Dq Li from
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option containing the pathname of a special device
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in addition to the options listed above.
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.Pp
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By default only the super-user may call the
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.Fn mount
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system call.
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This restriction can be removed by setting the
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.Va vfs.usermount
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.Xr sysctl 8
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variable
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to a non-zero value; see the BUGS section for more information.
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.Pp
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The following
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.Fa flags
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may be specified to
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suppress default semantics which affect file system access.
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.Bl -tag -width MNT_SYNCHRONOUS
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.It Dv MNT_RDONLY
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The file system should be treated as read-only;
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even the super-user may not write on it.
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Specifying MNT_UPDATE without this option will upgrade
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a read-only file system to read/write.
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.It Dv MNT_NOEXEC
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Do not allow files to be executed from the file system.
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.It Dv MNT_NOSUID
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Do not honor setuid or setgid bits on files when executing them.
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This flag is set automatically when the caller is not the super-user.
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.It Dv MNT_NOATIME
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Disable update of file access times.
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.It Dv MNT_SNAPSHOT
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Create a snapshot of the file system.
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This is currently only supported on UFS2 file systems, see
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.Xr mksnap_ffs 8
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for more information.
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.It Dv MNT_SUIDDIR
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Directories with the SUID bit set chown new files to their own owner.
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This flag requires the SUIDDIR option to have been compiled into the kernel
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to have any effect.
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See the
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.Xr mount 8
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and
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.Xr chmod 2
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pages for more information.
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.It Dv MNT_SYNCHRONOUS
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All I/O to the file system should be done synchronously.
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.It Dv MNT_ASYNC
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All I/O to the file system should be done asynchronously.
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.It Dv MNT_FORCE
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Force a read-write mount even if the file system appears to be unclean.
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Dangerous.
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Together with
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.Dv MNT_UPDATE
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and
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.Dv MNT_RDONLY ,
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specify that the file system is to be forcibly downgraded to a read-only
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mount even if some files are open for writing.
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.It Dv MNT_NOCLUSTERR
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Disable read clustering.
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.It Dv MNT_NOCLUSTERW
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Disable write clustering.
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.El
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.Pp
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The flag
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.Dv MNT_UPDATE
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indicates that the mount command is being applied
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to an already mounted file system.
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This allows the mount flags to be changed without requiring
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that the file system be unmounted and remounted.
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Some file systems may not allow all flags to be changed.
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For example,
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many file systems will not allow a change from read-write to read-only.
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.Pp
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The flag
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.Dv MNT_RELOAD
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causes the vfs subsystem to update its data structures pertaining to
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the specified already mounted file system.
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.Pp
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The
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.Fa type
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argument names the file system.
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The types of file systems known to the system can be obtained with
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.Xr lsvfs 1 .
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.Pp
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The
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.Fa data
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argument
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is a pointer to a structure that contains the type
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specific arguments to mount.
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The format for these argument structures is described in the
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manual page for each file system.
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By convention file system manual pages are named
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by prefixing ``mount_'' to the name of the file system as returned by
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.Xr lsvfs 1 .
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Thus the
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.Tn NFS
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file system is described by the
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.Xr mount_nfs 8
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manual page.
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It should be noted that a manual page for default
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file systems, known as UFS and UFS2, does not exist.
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.Pp
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The
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.Fn unmount
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system call disassociates the file system from the specified
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mount point
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.Fa dir .
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.Pp
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The
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.Fa flags
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argument may include
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.Dv MNT_FORCE
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to specify that the file system should be forcibly unmounted
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even if files are still active.
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Active special devices continue to work,
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but any further accesses to any other active files result in errors
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even if the file system is later remounted.
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.Pp
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If the
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.Dv MNT_BYFSID
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flag is specified,
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.Fa dir
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should instead be a file system ID encoded as
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.Dq Li FSID : Ns Ar val0 : Ns Ar val1 ,
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where
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.Ar val0
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and
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.Ar val1
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are the contents of the
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.Vt fsid_t
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.Va val[]
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array in decimal.
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The file system that has the specified file system ID will be unmounted.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn mount
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and
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.Fn nmount
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system calls will fail when one of the following occurs:
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.Bl -tag -width Er
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.It Bq Er EPERM
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The caller is neither the super-user nor the owner of
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.Fa dir .
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.It Bq Er ENAMETOOLONG
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A component of a pathname exceeded 255 characters,
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or the entire length of a path name exceeded 1023 characters.
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.It Bq Er ELOOP
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Too many symbolic links were encountered in translating a pathname.
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.It Bq Er ENOENT
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A component of
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.Fa dir
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does not exist.
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.It Bq Er ENOTDIR
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A component of
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.Fa name
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is not a directory,
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or a path prefix of
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.Fa special
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is not a directory.
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.It Bq Er EBUSY
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Another process currently holds a reference to
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.Fa dir .
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.It Bq Er EFAULT
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The
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.Fa dir
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argument
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points outside the process's allocated address space.
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.El
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.Pp
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The following errors can occur for a
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.Em ufs
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file system mount:
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.Bl -tag -width Er
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.It Bq Er ENODEV
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A component of ufs_args
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.Fa fspec
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does not exist.
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.It Bq Er ENOTBLK
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The
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.Fa fspec
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argument
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is not a block device.
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.It Bq Er ENXIO
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The major device number of
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.Fa fspec
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is out of range (this indicates no device driver exists
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for the associated hardware).
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.It Bq Er EBUSY
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.Fa fspec
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is already mounted.
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.It Bq Er EMFILE
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No space remains in the mount table.
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.It Bq Er EINVAL
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The super block for the file system had a bad magic
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number or an out of range block size.
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.It Bq Er ENOMEM
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Not enough memory was available to read the cylinder
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group information for the file system.
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.It Bq Er EIO
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An I/O error occurred while reading the super block or
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cylinder group information.
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.It Bq Er EFAULT
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The
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.Fa fspec
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argument
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points outside the process's allocated address space.
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.El
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.Pp
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The following errors can occur for a
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.Em nfs
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file system mount:
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.Bl -tag -width Er
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.It Bq Er ETIMEDOUT
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.Em Nfs
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timed out trying to contact the server.
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.It Bq Er EFAULT
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Some part of the information described by nfs_args
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points outside the process's allocated address space.
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.El
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.Pp
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The
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.Fn unmount
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system call may fail with one of the following errors:
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.Bl -tag -width Er
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.It Bq Er EPERM
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The caller is neither the super-user nor the user who issued the corresponding
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.Fn mount
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call.
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.It Bq Er ENAMETOOLONG
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The length of the path name exceeded 1023 characters.
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.It Bq Er EINVAL
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The requested directory is not in the mount table.
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.It Bq Er ENOENT
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The file system ID specified using
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.Dv MNT_BYFSID
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was not found in the mount table.
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.It Bq Er EINVAL
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The file system ID specified using
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.Dv MNT_BYFSID
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could not be decoded.
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.It Bq Er EINVAL
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The specified file system is the root file system.
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.It Bq Er EBUSY
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A process is holding a reference to a file located
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on the file system.
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.It Bq Er EIO
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An I/O error occurred while writing cached file system information.
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.It Bq Er EFAULT
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The
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.Fa dir
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argument
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points outside the process's allocated address space.
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.El
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.Sh SEE ALSO
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.Xr lsvfs 1 ,
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.Xr mksnap_ffs 8 ,
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.Xr mount 8 ,
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.Xr umount 8
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.Sh HISTORY
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The
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.Fn mount
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and
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.Fn unmount
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functions appeared in
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.At v6 .
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The
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.Fn nmount
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system call first appeared in
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.Fx 5.0 .
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.Sh BUGS
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Some of the error codes need translation to more obvious messages.
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.Pp
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Allowing untrusted users to mount arbitrary media, e.g. by enabling
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.Va vfs.usermount ,
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should not be considered safe.
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Most file systems in
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.Fx
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were not built to safeguard against malicious devices.
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