MOUNT(2)                  NetBSD System Calls Manual                  MOUNT(2)

NAME
     mount, 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,
         size_t data_len);

     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, and is data_len bytes long.  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_UNION        Union with underlying filesystem instead of obscuring
                      it.

     MNT_HIDDEN       Cause the df(1) program, and perhaps others, to, by
                      default, exclude this filesystem from its output.

     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 execut-
                      ing them.

     MNT_NODEV        Do not interpret special files on the file system.

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

     MNT_NOATIME      Never update access time in the file system.

     MNT_RELATIME     Update access time on write and change.  This helps pro-
                      grams that verify that the file has been read after
                      written to work.

     MNT_NODEVMTIME   Never update modification time of device files.

     MNT_SYMPERM      Recognize the permission of symbolic link when reading
                      or traversing.

     MNT_SYNCHRONOUS  All I/O to the file system should be done synchronously.
                      This will slow I/O performance considerably, but
                      enhances overall filesystem reliability.

     MNT_ASYNC        All I/O to the file system should be done asyn-
                      chronously.  This vastly improves I/O throughput, but at
                      a cost of making the filesystem likely to be completely
                      unrecoverable should the system crash while unwritten
                      data is pending in kernel buffers.

     MNT_LOG          Use a filesystem journal.  MNT_LOG causes a journal (or
                      log) to be created in the filesystem, creating a record
                      of meta-data writes to be performed, allowing the actual
                      writes to be deferred.  This improves performance in
                      most cases.

     MNT_EXTATTR      Enable extended attributes, if the filesystem supports
                      them and does not enable them by default.  Currently
                      this is only the case for UFS1.

     The MNT_UPDATE, MNT_RELOAD, and MNT_GETARGS flags indicate that the mount
     command is being applied to an already mounted file system.  The
     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 filesystem, unless the 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
     MNT_RELOAD flag causes kernel filesystem data to be reloaded from the
     filesystem device.  It is only permitted on filesystems mounted read-
     only.  Its purpose is to notify the system that the filesystem data has
     been modified by some external process.  The MNT_GETARGS flag does not
     alter any of the mounted filesystem's properties, but returns the
     filesystem-specific arguments for the currently mounted filesystem.

     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>, and those sup-
     ported by the current running kernel obtained using sysctl(8) to obtain
     the node vfs.generic.fstypes.  data is a pointer to a structure that con-
     tains the type specific arguments to mount.  Some of the currently sup-
     ported types of file systems and their type specific data are:

     MOUNT_FFS
           struct ufs_args {
                 char      *fspec;             /* block special file to mount */
           };

     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_args30 pad;  /* unused */
                 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 speci-
     fied 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 spe-
     cial 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
     mount() returns the value 0 if the mount was successful, the number of
     bytes written to data for MNT_GETARGS, 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:

     [EBUSY]            Another process currently holds a reference to dir, or
                        for an update from read-write to read-only there are
                        files on the filesystem open for writes.

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

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing a pathname.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} charac-
                        ters, or an entire path name exceeded {PATH_MAX} char-
                        acters.

     [ENOENT]           A component of dir does not exist.

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

     [EPERM]            The caller is not the super-user, and ordinary user
                        mounts are not permitted or this particular request
                        violates the rules.

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

     [EBUSY]            Fspec is already mounted.

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

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

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

     [EMFILE]           No space remains in the mount table.

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

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

     [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).

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

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

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

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

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

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

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

     [EMFILE]           No space remains in the mount table.

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

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

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

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

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

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

     [ELOOP]            Too many symbolic links were encountered in translat-
                        ing the pathname.

     [ENAMETOOLONG]     A component of a pathname exceeded {NAME_MAX} charac-
                        ters, or an entire path name exceeded {PATH_MAX} char-
                        acters.

     [ENOTDIR]          A component of the path is not a directory.

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

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

SEE ALSO
     df(1), getvfsstat(2), nfssvc(2), getmntinfo(3), symlink(7), mount(8),
     sysctl(8), umount(8)

HISTORY
     The mount() and umount() (now unmount()) function calls were all present
     in Version 6 AT&T UNIX.

     Prior to NetBSD 4.0 the mount call was used to export NFS filesystems.
     This is now done through nfssvc().

     The data_len argument was added for NetBSD 5.0.

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

     Far more filesystems are supported than those those listed.

NetBSD 6.1.4                   November 18, 2011                  NetBSD 6.1.4

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