MOUNT(2)

NAME
mount, unmount - mount or dismount a file system

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);

DESCRIPTION
The mount() function 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 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.

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.

MNT_NODEV
    Do not interpret special files on the file system.

MNT_UNION
    Union with underlying filesystem instead of obscuring it.

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

MNT_NOCOREDUMP
    Do not allow programs to dump core files on the file system.

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, most file systems will not allow a change from read-write to read-only.

The type argument defines the type of the file system. The types of file systems known to the system are defined in <sys/mount.h>. data is a pointer to a structure that contains the type specific arguments to mount. The currently supported types of file systems and their type specific data are:

MOUNT_FFS
    struct ufs_args {
          char      *fspec;             /* block special file to mount */
          struct    export_args export; /* network export information */
    };

MOUNT_NFS
    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 */
    };

MOUNT_MFS
    struct mfs_args {
          char	*fspec;             /* name to export for statfs */
          struct	export_args export; /* if we can export an MFS */
          caddr_t	base;               /* base of file system in mem */
          u_long	size;               /* size of file system */
    };

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

The flags argument may specify 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.

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.

Unmount returns the value 0 if the unmount succeeded; otherwise -1 is returned and the variable errno is set to indicate the error.

ERRORS
mount() will fail when one of the following occurs:

[EPERM]
    The caller is not the super-user.

[ENAMETOOLONG]
    A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} 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]
    dir 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]
    Fspec 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]
    Fspec 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 following errors can occur for a mfs file system mount:

[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]
    A paging error occurred while reading the super block or cylinder group information.

[EFAULT]
    Name points outside the process's allocated address space.

Unmount 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.

[ENAMETOOLONG]
    A component of a pathname exceeded {NAME_MAX} characters, or an entire path name exceeded {PATH_MAX} 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 file system.

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

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

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

SEE ALSO
getfsstat(2), getmntinfo(3), mount(8), umount(8), sysctl(8)

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

HISTORY
mount() and umount() (now unmount) function calls appeared in AT&T UNIX.