MOUNT(2) BSD System Calls Manual MOUNT(2)NAME
mount, unmount — mount or dismount a filesystem
SYNOPSIS
#include <sys/param.h>
#include <sys/mount.h>
int
mount(int type, const char *dir, int flags, caddr_t data);
int
unmount(const char *dir, int flags);
DESCRIPTION
The mount() function grafts a filesystem object onto the system file tree
at the point dir. The argument data describes the filesystem object to
be mounted. The argument type tells the kernel how to interpret data
(See type below). The contents of the filesystem become available
through the new mount point dir. Any files in dir at the time of a suc‐
cessful mount are swept under the carpet so to speak, and are unavailable
until the filesystem is unmounted.
The following flags may be specified to suppress default semantics which
affect filesystem access.
MNT_RDONLY The filesystem should be treated as read-only; Even the
super-user may not write on it.
MNT_NOEXEC Do not allow files to be executed from the filesystem.
MNT_NOSUID Do not honor setuid or setgid bits on files when execut‐
ing them.
MNT_NODEV Do not interpret special files on the filesystem.
MNT_SYNCHRONOUS All I/O to the filesystem should be done synchronously.
The flag MNT_UPDATE indicates that the mount command is being applied to
an already mounted filesystem. This allows the mount flags to be changed
without requiring that the filesystem be unmounted and remounted. Some
filesystems may not allow all flags to be changed. For example, most
filesystems will not allow a change from read-write to read-only.
The type argument names the filesystem. The types of filesystems known
to the system can be obtained with sysctl(8) by using the command:
sysctl vfs
Data is a pointer to a structure that contains the type specific argu‐
ments to mount. The format for these argument structures is described in
the manual page for each filesystem. By convention filesystem manual
pages are named by prefixing ``mount_'' to the name of the filesystem as
returned by sysctl(8). Thus the NFS filesystem is described by the
mount_nfs(8) manual page.
The umount() function call disassociates the filesystem from the speci‐
fied mount point dir.
The flags argument may specify MNT_FORCE to specify that the filesystem
should be forcibly unmounted even if files are still active. Active spe‐
cial devices continue to work, but any further accesses to any other
active files result in errors even if the filesystem is later remounted.
RETURN VALUES
The mount() returns the value 0 if the mount was successful, otherwise -1
is returned and the variable errno is set to indicate the error.
Umount returns the value 0 if the umount succeeded; otherwise -1 is
returned and the variable errno is set to indicate the error.
ERRORSMount() will fail when one of the following occurs:
[EPERM] The caller is not the super-user.
[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.
[EINVAL] A pathname contains a character with the high-order bit set.
[EBUSY] Another process currently holds a reference to dir.
[EFAULT] Dir points outside the process's allocated address space.
The following errors can occur for a ufs filesystem mount:
[ENODEV] A component of ufs_args fspec does not exist.
[ENOTBLK] Fspec is not a block device.
[ENXIO] The major device number of fspec is out of range (this indi‐
cates 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 filesystem 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 filesystem.
[EIO] An I/O error occurred while reading the super block or cylin‐
der group information.
[EFAULT] Fspec points outside the process's allocated address space.
The following errors can occur for a nfs filesystem mount:
[ETIMEDOUT]
Nfs timed out trying to contact the server.
[EFAULT] Some part of the information described by nfs_args points out‐
side the process's allocated address space.
The following errors can occur for a mfs filesystem mount:
[EMFILE] No space remains in the mount table.
[EINVAL] The super block for the filesystem 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 filesystem.
[EIO] A paging error occurred while reading the super block or
cylinder group information.
[EFAULT] Name points outside the process's allocated address space.
Umount may fail with one of the following errors:
[EPERM] The caller is not the super-user.
[ENOTDIR] A component of the path is not a directory.
[EINVAL] The pathname contains a character with the high-order bit set.
[ENAMETOOLONG]
A component of a pathname exceeded 255 characters, or an
entire path name exceeded 1023 characters.
[ELOOP] Too many symbolic links were encountered in translating the
pathname.
[EINVAL] The requested directory is not in the mount table.
[EBUSY] A process is holding a reference to a file located on the
filesystem.
[EIO] An I/O error occurred while writing cached filesystem informa‐
tion.
[EFAULT] Dir points outside the process's allocated address space.
A ufs or mfs mount can also fail if the maximum number of filesystems are
currently mounted.
SEE ALSOmount(8), umount(8), sysctl(8)BUGS
Some of the error codes need translation to more obvious messages.
HISTORYMount() and umount() function calls appeared in Version 6 AT&T UNIX.
4th Berkeley Distribution May 24, 1995 4th Berkeley Distribution
