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 successful 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 executing them.

MNT_NOATIME
    Disable update of file access times.

MNT_NODEV
    Do not interpret special files on the filesystem.

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

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

MNT_WANTRDWR
    Upgrade a mounted read-only filesystem to read-write if MNT_UPDATE is also specified.

MNT_FORCE
    Force a read-write mount even if the filesystem appears to be unclean. Dangerous.

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, many filesystems 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 filesystem.

The type argument defines the type of the filesystem. The types of filesystems 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 filesystems and their type specific data are:

    /*
     * Export arguments for local filesystem mount calls.
     */
    struct export_args {
    	int	ex_flags;		/* export related flags */
    	uid_t	ex_root;		/* mapping for root uid */
    	struct	ucred ex_anon;		/* mapping for anonymous user */
    	struct	sockaddr *ex_addr;	/* net address to which exported */
    	int	ex_addrlen;		/* and the net address length */
    	struct	sockaddr *ex_mask;	/* mask of valid bits in saddr */
    	int	ex_masklen;		/* and the smask length */
    };

MOUNT_UFS

    /*
     * Arguments to mount UFS-bases filesystems
     */
    struct ufs_args {
          char	*fspec;               /* Block special file to mount */
          struct	export_args export;   /* network export information */
    };

MOUNT_NFS

    #ifdef NFS
    /*
     * Arguments to mount NFS
     */
    struct nfs_args {
    	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 */
    };
    /*
     * NFS mount option flags
     */
    #define	NFSMNT_SOFT		0x00000001  /* soft mount (hard is default) */
    #define	NFSMNT_WSIZE		0x00000002  /* set write size */
    #define	NFSMNT_RSIZE		0x00000004  /* set read size */
    #define	NFSMNT_TIMEO		0x00000008  /* set initial timeout */
    #define	NFSMNT_RETRANS		0x00000010  /* set number of request retries */
    #define	NFSMNT_MAXGRPS		0x00000020  /* set maximum grouplist size */
    #define	NFSMNT_INT		0x00000040  /* allow interrupts on hard mount */
    #define	NFSMNT_NOCONN		0x00000080  /* Don't Connect the socket */
    #define	NFSMNT_NQNFS		0x00000100  /* Use Nqnfs protocol */
    #define	NFSMNT_NFSV3		0x00000200  /* Use NFS Version 3 protocol */
    #define	NFSMNT_KERB		0x00000400  /* Use Kerberos authentication */
    #define	NFSMNT_DUMBTIMR		0x00000800  /* Don't estimate rtt dynamically */
    #define	NFSMNT_LEASETERM	0x00001000  /* set lease term (nqnfs) */
    #define	NFSMNT_READAHEAD	0x00002000  /* set read ahead */
    #define	NFSMNT_DEADTHRESH	0x00004000  /* set dead server retry thresh */
    #define	NFSMNT_RESVPORT		0x00008000  /* Allocate a reserved port */
    #define	NFSMNT_RDIRPLUS		0x00010000  /* Use Readdirplus for V3 */
    #define	NFSMNT_READDIRSIZE	0x00020000  /* Set readdir size */
    #define	NFSMNT_INTERNAL		0xfffc0000  /* Bits set internally */
    #define NFSMNT_HASWRITEVERF	0x00040000  /* Has write verifier for V3 */
    #define NFSMNT_GOTPATHCONF	0x00080000  /* Got the V3 pathconf info */
    #define NFSMNT_GOTFSINFO	0x00100000  /* Got the V3 fsinfo */
    #define	NFSMNT_MNTD		0x00200000  /* Mnt server for mnt point */
    #define	NFSMNT_DISMINPROG	0x00400000  /* Dismount in progress */
    #define	NFSMNT_DISMNT		0x00800000  /* Dismounted */
    #define	NFSMNT_SNDLOCK		0x01000000  /* Send socket lock */
    #define	NFSMNT_WANTSND		0x02000000  /* Want above */
    #define	NFSMNT_RCVLOCK		0x04000000  /* Rcv socket lock */
    #define	NFSMNT_WANTRCV		0x08000000  /* Want above */
    #define	NFSMNT_WAITAUTH		0x10000000  /* Wait for authentication */
    #define	NFSMNT_HASAUTH		0x20000000  /* Has authenticator */
    #define	NFSMNT_WANTAUTH		0x40000000  /* Wants an authenticator */
    #define	NFSMNT_AUTHERR		0x80000000  /* Authentication error */
    #endif /* NFS */

MOUNT_MFS

    /*
     * Arguments to mount MFS
     */
    struct mfs_args {
          char	*fspec; /* name to export for statfs */
          struct	export_args export; /* if exported MFSes are supported */
          caddr_t	base;   /* base of file system in memory */
          u_long	size;   /* size of file system */
    };

MOUNT_MSDOS

    #ifdef MSDOSFS
    /*
     *  Arguments to mount MSDOS filesystems.
     */
    struct msdosfs_args {
    	char	*fspec;		/* blocks special holding the fs to mount */
    	struct	export_args export;	/* network export information */
    	uid_t	uid;		/* uid that owns msdosfs files */
    	gid_t	gid;		/* gid that owns msdosfs files */
    	mode_t	mask;		/* mask to be applied for msdosfs perms */
    	int	flags;		/* see below */
    	int magic;		/* version number */
    	u_int16_t u2w[128];     /* Local->Unicode table */
    	u_int8_t  ul[128];      /* Local upper->lower table */
    	u_int8_t  lu[128];      /* Local lower->upper table */
    	u_int8_t  d2u[128];     /* DOS->local table */
    	u_int8_t  u2d[128];     /* Local->DOS table */
    };
    #endif

MOUNT_CD9660

    #ifdef CD9660
    /*
     * Arguments to mount ISO 9660 filesystems.
     */
    struct iso_args {
    	char *fspec;			/* block special device to mount */
    	struct	export_args export;	/* network export info */
    	int flags;			/* mounting flags, see below */
    };
    #define ISOFSMNT_NORRIP	0x00000001 /* disable Rock Ridge Ext.*/
    #define ISOFSMNT_GENS	0x00000002 /* enable generation numbers */
    #define ISOFSMNT_EXTATT	0x00000004 /* enable extended attributes */
    #endif /* CD9660 */

The umount() function call disassociates the filesystem from the specified mount point dir.

The flags argument may specify MNT_FORCE to specify that the filesystem should be forcibly unmounted or made read-only (if MNT_UPDATE and MNT_RDONLY are also specified) 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 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.

The umount() function returns the value 0 if the umount succeeded; otherwise -1 is returned and the variable errno is set to indicate the error.

ERRORS
The mount() function 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.

[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 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 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 cylinder 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 outside 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.

The umount() function 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 information.

[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 ALSO
mfs(8), mount(8), umount(8)

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

HISTORY
Mount() and umount() function calls appeared in AT&T UNIX.