mount (2)

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(The comments found at the beginning of the groff file "man2/mount.2freebsd".)

NAME

mount nmount unmount - mount or dismount a file system

LIBRARY

Lb libc

SYNOPSIS

In sys/param.h In sys/mount.h Ft int Fn mount const char *type const char *dir int flags void *data Ft int Fn unmount const char *dir int flags In sys/uio.h Ft int Fn nmount struct iovec *iov u_int niov int flags

DESCRIPTION

The Fn mount system call grafts a file system object onto the system file tree at the point Fa dir . The argument Fa data describes the file system object to be mounted. The argument Fa type tells the kernel how to interpret Fa data (See Fa type below). The contents of the file system become available through the new mount point Fa dir . Any files in Fa 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 Fn nmount system call behaves similarly to Fn 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 Fa iov , containing Fa niov elements. The following options are required by all file systems:

fstype Ta file system type name (e.g., ``procfs ''

fspath Ta 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 Fn 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 Fa 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_ffs8 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 Fa type argument names the file system. The types of file systems known to the system can be obtained with lsvfs(1).

The Fa 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_nfs8 manual page. It should be noted that a manual page for default file systems, known as UFS and UFS2, does not exist.

The Fn unmount system call disassociates the file system from the specified mount point Fa dir .

The Fa 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, Fa dir should instead be a file system ID encoded as ``FSID : val0 : val1 '' where val0 and val1 are the contents of the Vt fsid_t val[] array in decimal. The file system that has the specified file system ID will be unmounted.

RETURN VALUES

Rv -std

ERRORS

The Fn mount and Fn nmount system calls will fail when one of the following occurs:

Bq Er EPERM

The caller is neither the super-user nor the owner of Fa dir .

Bq Er ENAMETOOLONG

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

Bq Er ELOOP

Too many symbolic links were encountered in translating a pathname.

Bq Er ENOENT

A component of Fa dir does not exist.

Bq Er ENOTDIR

A component of Fa name is not a directory, or a path prefix of Fa special is not a directory.

Bq Er EBUSY

Another process currently holds a reference to Fa dir .

Bq Er EFAULT

The Fa dir argument points outside the process's allocated address space.

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

Bq Er ENODEV

A component of ufs_args Fa fspec does not exist.

Bq Er ENOTBLK

The Fa fspec argument is not a block device.

Bq Er ENXIO

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

Bq Er EBUSY

Fa fspec is already mounted.

Bq Er EMFILE

No space remains in the mount table.

Bq Er EINVAL

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

Bq Er ENOMEM

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

Bq Er EIO

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

Bq Er EFAULT

The Fa fspec argument points outside the process's allocated address space.

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

Bq Er ETIMEDOUT

Nfs timed out trying to contact the server.

Bq Er EFAULT

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

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

Bq Er EPERM

The caller is neither the super-user nor the user who issued the corresponding Fn mount call.

Bq Er ENAMETOOLONG

The length of the path name exceeded 1023 characters.

Bq Er EINVAL

The requested directory is not in the mount table.

Bq Er ENOENT

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

Bq Er EINVAL

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

Bq Er EINVAL

The specified file system is the root file system.

Bq Er EBUSY

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

Bq Er EIO

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

Bq Er EFAULT

The Fa dir argument points outside the process's allocated address space.

A ufs mount can also fail if the maximum number of file systems are currently mounted.

SEE ALSO

lsvfs(1), mksnap_ffs8, mount(8), umount(8)

HISTORY

The Fn mount and Fn unmount functions appeared in AT&T System v6 . The Fn nmount system call first appeared in Fx 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 Fx were not built to safeguard against malicious devices.