379 lines
10 KiB
Groff
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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.\" 4. 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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