unmount

MOUNT(2)                     BSD System Calls Manual                    MOUNT(2)

NAME
     mount, nmount, unmount — mount or dismount a file system

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <sys/param.h>
     #include <sys/mount.h>

     int
     mount(const char *type, const char *dir, int flags, void *data);

     int
     unmount(const char *dir, int flags);

     #include <sys/uio.h>

     int
     nmount(struct iovec *iov, u_int niov, int flags);

DESCRIPTION
     The mount() system call grafts a file system object onto the system file
     tree at the point dir.  The argument data describes the file system object
     to be mounted.  The argument type tells the kernel how to interpret data
     (See type below).  The contents of the file system become available through
     the new mount point dir.  Any files in 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.

     The nmount() system call behaves similarly to mount(), except that the
     mount options (file system type name, device to mount, mount-point name,
     etc.) are passed as an array of name-value pairs in the array iov,
     containing niov elements.  The following options are required by all file
     systems:

           fstype    file system type name (e.g., “procfs”)
           fspath    mount point pathname (e.g., “/proc”)

     Depending on the file system type, other options may be recognized or
     required; for example, most disk-based file systems require a “from” option
     containing the pathname of a special device in addition to the options
     listed above.

     By default only the super-user may call the mount() system call.  This
     restriction can be removed by setting the vfs.usermount sysctl(8) variable
     to a non-zero value; see the BUGS section for more information.

     The following flags may be specified to suppress default semantics which
     affect file system access.

     MNT_RDONLY       The file system should be treated as read-only; even the
                      super-user may not write on it.  Specifying MNT_UPDATE
                      without this option will upgrade a read-only file system
                      to read/write.

     MNT_NOEXEC       Do not allow files to be executed from the file system.

     MNT_NOSUID       Do not honor setuid or setgid bits on files when executing
                      them.  This flag is set automatically when the caller is
                      not the super-user.

     MNT_NOATIME      Disable update of file access times.

     MNT_SNAPSHOT     Create a snapshot of the file system.  This is currently
                      only supported on UFS2 file systems, see mksnap_ffs(8) for
                      more information.

     MNT_SUIDDIR      Directories with the SUID bit set chown new files to their
                      own owner.  This flag requires the SUIDDIR option to have
                      been compiled into the kernel to have any effect.  See the
                      mount(8) and chmod(2) pages for more information.

     MNT_SYNCHRONOUS  All I/O to the file system should be done synchronously.

     MNT_ASYNC        All I/O to the file system should be done asynchronously.

     MNT_FORCE        Force a read-write mount even if the file system appears
                      to be unclean.  Dangerous.  Together with MNT_UPDATE and
                      MNT_RDONLY, specify that the file system is to be forcibly
                      downgraded to a read-only mount even if some files are
                      open for writing.

     MNT_NOCLUSTERR   Disable read clustering.

     MNT_NOCLUSTERW   Disable write clustering.

     The flag MNT_UPDATE indicates that the mount command is being applied to an
     already mounted file system.  This allows the mount flags to be changed
     without requiring that the file system be unmounted and remounted.  Some
     file systems may not allow all flags to be changed.  For example, many file
     systems will not allow a change from read-write to read-only.

     The flag MNT_RELOAD causes the vfs subsystem to update its data structures
     pertaining to the specified already mounted file system.

     The type argument names the file system.  The types of file systems known
     to the system can be obtained with lsvfs(1).

     The data argument is a pointer to a structure that contains the type
     specific arguments to mount.  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 lsvfs(1).  Thus the NFS file system is described
     by the mount_nfs(8) manual page.  It should be noted that a manual page for
     default file systems, known as UFS and UFS2, does not exist.

     The unmount() system call disassociates the file system from the specified
     mount point dir.

     The flags argument may include 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.

     If the MNT_BYFSID flag is specified, dir should instead be a file system ID
     encoded as “FSID:val0:val1”, where val0 and val1 are the contents of the
     fsid_t val[] array in decimal.  The file system that has the specified file
     system ID will be unmounted.

RETURN VALUES
     Upon successful completion, the value 0 is returned; otherwise the value -1
     is returned and the global variable errno is set to indicate the error.

ERRORS
     The mount() and nmount() system calls will fail when one of the following
     occurs:

     [EPERM]            The caller is neither the super-user nor the owner of
                        dir.

     [ENAMETOOLONG]     A component of a pathname exceeded 255 characters, or
                        the entire length of a path name exceeded 1023
                        characters.

     [ELOOP]            Too many symbolic links were encountered in translating
                        a pathname.

     [ENOENT]           A component of dir does not exist.

     [ENOTDIR]          A component of name is not a directory, or a path prefix
                        of special is not a directory.

     [EBUSY]            Another process currently holds a reference to dir.

     [EFAULT]           The dir argument points outside the process's allocated
                        address space.

     The following errors can occur for a ufs file system mount:

     [ENODEV]           A component of ufs_args fspec does not exist.

     [ENOTBLK]          The fspec argument is not a block device.

     [ENXIO]            The major device number of fspec is out of range (this
                        indicates no device driver exists for the associated
                        hardware).

     [EBUSY]            fspec is already mounted.

     [EMFILE]           No space remains in the mount table.

     [EINVAL]           The super block for the file system had a bad magic
                        number or an out of range block size.

     [ENOMEM]           Not enough memory was available to read the cylinder
                        group information for the file system.

     [EIO]              An I/O error occurred while reading the super block or
                        cylinder group information.

     [EFAULT]           The fspec argument points outside the process's
                        allocated address space.

     The following errors can occur for a nfs file system mount:

     [ETIMEDOUT]        Nfs timed out trying to contact the server.

     [EFAULT]           Some part of the information described by nfs_args
                        points outside the process's allocated address space.

     The unmount() system call may fail with one of the following errors:

     [EPERM]            The caller is neither the super-user nor the user who
                        issued the corresponding mount() call.

     [ENAMETOOLONG]     The length of the path name exceeded 1023 characters.

     [EINVAL]           The requested directory is not in the mount table.

     [ENOENT]           The file system ID specified using MNT_BYFSID was not
                        found in the mount table.

     [EINVAL]           The file system ID specified using MNT_BYFSID could not
                        be decoded.

     [EINVAL]           The specified file system is the root file system.

     [EBUSY]            A process is holding a reference to a file located on
                        the file system.

     [EIO]              An I/O error occurred while writing cached file system
                        information.

     [EFAULT]           The dir argument points outside the process's allocated
                        address space.

SEE ALSO
     lsvfs(1), mksnap_ffs(8), mount(8), umount(8)

HISTORY
     The mount() and unmount() functions appeared in Version 1 AT&T UNIX.  The
     nmount() system call first appeared in FreeBSD 5.0.

BUGS
     Some of the error codes need translation to more obvious messages.

     Allowing untrusted users to mount arbitrary media, e.g. by enabling
     vfs.usermount, should not be considered safe.  Most file systems in FreeBSD
     were not built to safeguard against malicious devices.

BSD                             December 1, 2017                             BSD