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.\"     @(#)mount.2	8.3 (Berkeley) 5/24/95
.\"
.Dd September 2, 2019
.Dt MOUNT 2
.Os
.Sh NAME
.Nm mount ,
.Nm unmount
.Nd mount or dismount a file system
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/param.h
.In sys/mount.h
.Ft int
.Fn mount "const char *type" "const char *dir" "int flags" "void *data" "size_t data_len"
.Ft int
.Fn unmount "const char *dir" "int flags"
.Sh DESCRIPTION
The
.Fn mount
function grafts
a file system object onto the system file tree
at the point
.Ar dir .
The argument
.Ar data
describes the file system object to be mounted, and is
.Ar data_len
bytes long.
The argument
.Ar type
tells the kernel how to interpret
.Ar data
(See
.Ar type
below).
The contents of the file system
become available through the new mount point
.Ar dir .
Any files in
.Ar dir
at the time
of a successful mount are swept under the carpet so to speak, and
are unavailable until the file system is unmounted.
.Pp
The following
.Ar flags
may be specified to
suppress default semantics which affect file system access.
.Bl -tag -width MNT_SYNCHRONOUS
.It Dv MNT_RDONLY
The file system should be treated as read-only;
even the super-user may not write on it.
.It Dv MNT_UNION
Union with underlying file system instead of obscuring it.
.It Dv MNT_HIDDEN
Cause the
.Xr df 1
program, and perhaps others, to, by default,
exclude this file system from its output.
.It Dv MNT_NOEXEC
Do not allow files to be executed from the file system.
.It Dv MNT_NOSUID
Do not honor setuid or setgid bits on files when executing them.
.It Dv MNT_NODEV
Do not interpret special files on the file system.
.It Dv MNT_NOCOREDUMP
Do not allow programs to dump core files on the file system.
.It Dv MNT_NOATIME
Never update access time in the file system.
.It Dv MNT_RELATIME
Update access time on write and change.
This helps programs that verify that the file has been read after written
to work.
.It Dv MNT_NODEVMTIME
Never update modification time of device files.
.It Dv MNT_SYMPERM
Recognize the permission of symbolic link when reading or traversing.
.It Dv MNT_SYNCHRONOUS
All I/O to the file system should be done synchronously.
This will slow I/O performance considerably, but
enhances overall file system reliability.
.It Dv MNT_ASYNC
All I/O to the file system should be done asynchronously.
This vastly improves I/O throughput,
but at a cost of making the file system likely to be
completely unrecoverable should the system crash while
unwritten data is pending in kernel buffers.
.It Dv MNT_LOG
Use a file system journal.
.Dv MNT_LOG
causes a journal (or log) to be created in the
file system, creating a record of meta-data writes to be
performed, allowing the actual writes to be deferred.
This improves performance in most cases.
.It MNT_EXTATTR
Enable extended attributes, if the file system supports them and
does not enable them by default.
Currently this is only the case for UFS1.
.El
.Pp
The
.Dv MNT_UPDATE ,
.Dv MNT_RELOAD ,
and
.Dv MNT_GETARGS
flags indicate that the mount command is being applied
to an already mounted file system.
The
.Dv MNT_UPDATE
flag allows the mount flags to be changed without requiring
that the file system be unmounted and remounted.
A conversion from read-write to read-only will fail if any files
are currently open for writing on the file system, unless the
.Dv MNT_FORCE
flag is also applied.
Some file systems may not allow all flags to be changed.
For example,
some file systems will not allow a change from read-write to read-only.
The
.Dv MNT_RELOAD
flag causes kernel file system data to be reloaded from
the file system device.
It is only permitted on file systems mounted read-only.
Its purpose is to notify the system that the file system
data has been modified by some external process.
The
.Dv MNT_GETARGS
flag does not alter any of the mounted file system's properties,
but returns the file system-specific arguments for the currently mounted
file system.
.Pp
The
.Fa type
argument defines the type of the file system.
The types of file systems known to the system are defined in
.In sys/mount.h ,
and those supported by the current running kernel obtained
using
.Xr sysctl 8
to obtain the node
.\" .Bd -literal -offset indent
vfs.generic.fstypes.
.\" XXX from lite-2:
.\" The types of file systems known to the system can be obtained with
.\" .Xr sysctl 8
.\" by using the command:
.\" .Bd -literal -offset indent
.\" sysctl vfs
.\" .Ed
.\" .Pp
.Fa data
is a pointer to a structure that contains the type
specific arguments to mount.
Some of the currently supported types of file systems and
their type specific data are:
.Pp
.Dv MOUNT_FFS
.Bd -literal -offset indent -compact
struct ufs_args {
      char      *fspec;             /* block special file to mount */
};
.Ed
.Pp
.Dv MOUNT_NFS
.Bd -literal -offset indent -compact
struct nfs_args {
      int             version;      /* args structure version */
      struct sockaddr *addr;        /* file server address */
      int             addrlen;      /* length of address */
      int             sotype;       /* Socket type */
      int             proto;        /* and Protocol */
      u_char          *fh;          /* File handle to be mounted */
      int             fhsize;       /* Size, in bytes, of fh */
      int             flags;        /* flags */
      int             wsize;        /* write size in bytes */
      int             rsize;        /* read size in bytes */
      int             readdirsize;  /* readdir size in bytes */
      int             timeo;        /* initial timeout in .1 secs */
      int             retrans;      /* times to retry send */
      int             maxgrouplist; /* Max. size of group list */
      int             readahead;    /* # of blocks to readahead */
      int             leaseterm;    /* Term (sec) of lease */
      int             deadthresh;   /* Retrans threshold */
      char            *hostname;    /* server's name */
};
.Ed
.Pp
.Dv MOUNT_MFS
.Bd -literal -offset indent -compact
struct mfs_args {
      char	*fspec;             /* name to export for statfs */
      struct	export_args30 pad;  /* unused */
      caddr_t	base;               /* base of file system in mem */
      u_long	size;               /* size of file system */
};
.Ed
.\" XXX from lite-2:
.\" The format for these argument structures is described in the
.\" manual page for each file system.
.\" By convention file system manual pages are named
.\" by prefixing ``mount_'' to the name of the file system as returned by
.\" .Xr sysctl 8 .
.\" Thus the
.\" .Nm NFS
.\" file system is described by the
.\" .Xr mount_nfs 8
.\" manual page.
.Pp
The
.Fn unmount
function call disassociates the file system from the specified
mount point
.Fa dir .
.Pp
The
.Fa flags
argument may specify
.Dv MNT_FORCE
to specify that the file system should be forcibly unmounted even if files are
still active.
Active special devices continue to work,
but any further accesses to any other active files result in errors
even if the file system is later remounted.
.Sh RETURN VALUES
.Fn mount
returns the value 0 if the mount was successful,
the number of bytes written to
.Ar data
for
.Dv MNT_GETARGS ,
otherwise \-1 is returned and the variable
.Va errno
is set to indicate the error.
.Pp
.Fn unmount
returns the value 0 if the unmount succeeded; otherwise \-1 is returned
and the variable
.Va errno
is set to indicate the error.
.Sh ERRORS
.Fn mount
will fail when one of the following occurs:
.Bl -tag -width Er
.It Bq Er EBUSY
Another process currently holds a reference to
.Fa dir ,
or for an update from read-write to read-only
there are files on the file system open for writes.
.It Bq Er EFAULT
.Fa dir
points outside the process's allocated address space.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating a pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOENT
A component of
.Fa dir
does not exist.
.It Bq Er ENOTDIR
A component of
.Ar name
is not a directory,
or a path prefix of
.Ar special
is not a directory.
.It Bq Er EPERM
The caller is not the super-user,
and ordinary user mounts are not permitted or
this particular request violates the rules.
.El
.Pp
The following errors can occur for a
.Em ufs
file system mount:
.Bl -tag -width Er
.It Bq Er EBUSY
.Ar Fspec
is already mounted.
.It Bq Er EFAULT
.Ar Fspec
points outside the process's allocated address space.
.It Bq Er EINVAL
The super block for the file system had a bad magic
number or an out of range block size.
.It Bq Er EIO
An I/O error occurred while reading the super block or
cylinder group information.
.It Bq Er EMFILE
No space remains in the mount table.
.It Bq Er ENODEV
A component of ufs_args
.Ar fspec
does not exist.
.It Bq Er ENOMEM
Not enough memory was available to read the cylinder
group information for the file system.
.It Bq Er ENOTBLK
.Ar Fspec
is not a block device.
.It Bq Er ENXIO
The major device number of
.Ar fspec
is out of range (this indicates no device driver exists
for the associated hardware).
.El
.Pp
The following errors can occur for a
.Em nfs
file system mount:
.Bl -tag -width Er
.It Bq Er EFAULT
Some part of the information described by nfs_args
points outside the process's allocated address space.
.It Bq Er ETIMEDOUT
.Em Nfs
timed out trying to contact the server.
.El
.Pp
The following errors can occur for a
.Em mfs
file system mount:
.Bl -tag -width Er
.It Bq Er EFAULT
.Em Name
points outside the process's allocated address space.
.It Bq Er EINVAL
The super block for the file system had a bad magic
number or an out of range block size.
.It Bq Er EIO
A paging error occurred while reading the super block or
cylinder group information.
.It Bq Er EMFILE
No space remains in the mount table.
.It Bq Er ENOMEM
Not enough memory was available to read the cylinder
group information for the file system.
.El
.Pp
.Fn unmount
may fail with one of the following errors:
.Bl -tag -width Er
.It Bq Er EBUSY
A process is holding a reference to a file located
on the file system.
.It Bq Er EFAULT
.Fa dir
points outside the process's allocated address space.
.It Bq Er EINVAL
The requested directory is not in the mount table.
.It Bq Er EIO
An I/O error occurred while writing cached file system information.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOTDIR
A component of the path is not a directory.
.It Bq Er EPERM
The caller is not the super-user.
.El
.Pp
A
.Em ufs
or
.Em mfs
mount can also fail if the maximum number of file systems are currently
mounted.
.Sh SEE ALSO
.Xr df 1 ,
.Xr getvfsstat 2 ,
.Xr nfssvc 2 ,
.Xr getmntinfo 3 ,
.Xr symlink 7 ,
.Xr mount 8 ,
.Xr sysctl 8 ,
.Xr umount 8
.Sh HISTORY
The
.Fn mount
and
.Fn umount
(now
.Fn unmount )
functions appeared in
.At v1 .
.Pp
Prior to
.Nx 4.0
the
.Nm
call was used to export NFS file systems.
This is now done through
.Fn nfssvc .
.Pp
The
.Dv data_len
argument was added for
.Nx 5.0 .
.Sh BUGS
Some of the error codes need translation to more obvious messages.
.Pp
Far more file systems are supported than those those listed.