path: root/lib/libc/sys/mount.2

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.Dd $Mdocdate: January 3 2021 $
.Dt MOUNT 2
.Os
.Sh NAME
.Nm mount ,
.Nm unmount
.Nd mount or dismount a filesystem
.Sh SYNOPSIS
.In sys/types.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"
.Sh DESCRIPTION
The
.Fn mount
function grafts
a filesystem object onto the system file tree
at the point
.Fa dir .
The argument
.Fa data
describes the filesystem object to be mounted.
The argument
.Fa type
tells the kernel how to interpret
.Fa data
(see
.Fa type
below).
The contents of the filesystem
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 filesystem is unmounted.
.Pp
The following
.Fa flags
may be specified to
suppress default semantics which affect filesystem access.
.Bl -tag -width MNT_SYNCHRONOUS
.It Dv MNT_RDONLY
The filesystem should be treated as read-only:
even the superuser may not write to it.
.It Dv MNT_NOATIME
Do not update the access time on files in the filesystem unless
the modification or status change times are also being updated.
.It Dv MNT_NOEXEC
Do not allow files to be executed from the filesystem.
.It Dv MNT_NOSUID
Do not honor setuid or setgid bits on files when executing them.
.It Dv MNT_NODEV
Do not interpret special files on the filesystem.
.It Dv MNT_SYNCHRONOUS
All I/O to the filesystem should be done synchronously.
.It Dv MNT_ASYNC
All I/O to the filesystem should be done asynchronously.
.It Dv MNT_SOFTDEP
Use soft dependencies.
Applies to FFS filesystems only (see 'softdep' in
.Xr mount 8 ) .
.It Dv MNT_WXALLOWED
Processes that ask for memory to be made writeable plus executable
using the
.Xr mmap 2
and
.Xr mprotect 2
system calls are killed by default.
This option allows those processes to continue operation.
The option is typically used on the
.Pa /usr/local
filesystem.
.El
.Pp
The flag
.Dv 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.
.Pp
The
.Fa type
argument defines the type of the filesystem.
The types of filesystems known to the system are defined in
.In sys/mount.h .
.Fa 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:
.Pp
.Dv MOUNT_CD9660
.Bd -literal -offset indent -compact
struct iso_args {
    char	*fspec;	    /* block special device to mount */
    struct	export_args export_info;
    			    /* 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 */
#define	ISOFSMNT_NOJOLIET 0x00000008 /* disable Joliet Ext.*/
#define	ISOFSMNT_SESS	  0x00000010 /* use iso_args.sess */
.Ed
.Pp
.Dv MOUNT_FFS
.Bd -literal -offset indent -compact
struct ufs_args {
      char      *fspec;             /* block special file to mount */
      struct    export_args export_info;
      				    /* network export information */
};
.Ed
.Pp
.Dv MOUNT_MFS
.Bd -literal -offset indent -compact
struct mfs_args {
      char	*fspec;             /* name to export for statfs */
      struct	export_args export_info;
      				    /* if we can export an MFS */
      caddr_t	base;               /* base of filesystem in mem */
      u_long	size;               /* size of filesystem */
};
.Ed
.Pp
.Dv MOUNT_MSDOS
.Bd -literal -offset indent -compact
struct msdosfs_args {
	char	*fspec;	   /* blocks special holding fs to mount */
	struct	export_args export_info;
			   /* 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 */
};

/*
 * Msdosfs mount options:
 */
#define	MSDOSFSMNT_SHORTNAME 1  /* Force old DOS short names only */
#define	MSDOSFSMNT_LONGNAME  2  /* Force Win'95 long names */
#define	MSDOSFSMNT_NOWIN95   4  /* Completely ignore Win95 entries */
.Ed
.Pp
.Dv MOUNT_NFS
.Bd -literal -offset indent -compact
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 */
      int	acregmin;     /* Attr cache file recently modified */
      int	acregmax;     	/* ac file not recently modified */
      int	acdirmin;     	/* ac for dir recently modified */
      int	acdirmax;     /* ac for dir not recently modified */
};
.Ed
.Pp
.Dv MOUNT_NTFS
.Bd -literal -offset indent -compact
struct ntfs_args {
        char    *fspec;	/* block special device to mount */
        struct  export_args export_info;
			/* network export information */
        uid_t   uid;	/* uid that owns ntfs files */
        gid_t   gid;	/* gid that owns ntfs files */
        mode_t  mode;	/* mask to be applied for ntfs perms */
        u_long  flag;	/* additional flags */
};

/*
 * ntfs mount options:
 */
#define     NTFS_MFLAG_CASEINS      0x00000001
#define     NTFS_MFLAG_ALLNAMES     0x00000002
.Ed
.Pp
.Dv MOUNT_UDF
.Bd -literal -offset indent -compact
struct udf_args {
	char	*fspec;	/* block special device to mount */
};
.Ed
.Pp
The
.Fn unmount
function call disassociates the filesystem from the specified
mount point
.Fa dir .
.Pp
The
.Fa flags
argument may specify
.Dv MNT_FORCE
to specify that the filesystem 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 filesystem is later remounted.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn mount
will fail when one of the following occurs:
.Bl -tag -width [ENAMETOOLONG]
.It Bq Er EPERM
The caller is not the superuser.
.It Bq Er ENAMETOOLONG
The pathname exceeded
.Dv MNAMELEN
characters.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating a pathname.
.It Bq Er ENOENT
A component of
.Fa dir
does not exist.
.It Bq Er ENOTDIR
A component of
.Ar name
is not a directory,
or a path prefix of
.Ar special
is not a directory.
.It Bq Er EINVAL
An argument given was invalid.
.It Bq Er EBUSY
Another process currently holds a reference to
.Fa dir .
.It Bq Er EFAULT
.Fa dir
points outside the process's allocated address space.
.It Bq Er EOPNOTSUPP
.Fa type
is not supported by the kernel.
.El
.Pp
The following errors can occur for a
.Dq ufs
filesystem mount:
.Bl -tag -width [ENOTBLK]
.It Bq Er ENODEV
A component of ufs_args
.Fa fspec
does not exist.
.It Bq Er ENOTBLK
.Fa fspec
is not a block device.
.It Bq Er ENXIO
The major device number of
.Fa fspec
is out of range (this indicates no device driver exists
for the associated hardware).
.It Bq Er EBUSY
.Fa fspec
is already mounted.
.It Bq Er EINVAL
The super block for the filesystem had a bad magic number, an out of range
block size, or an invalid combination of flags.
.It Bq Er ENOMEM
Not enough memory was available to read the cylinder
group information for the filesystem.
.It Bq Er EIO
An I/O error occurred while reading the super block or
cylinder group information.
.It Bq Er EFAULT
.Fa fspec
points outside the process's allocated address space.
.It Bq Er EROFS
The filesystem was not unmounted cleanly and
.Dv MNT_FORCE
was not specified.
.It Bq Er EROFS
An attempt was made to mount a
.Bx 4.2
filesystem without the
.Dv MNT_RDONLY
flag.
.El
.Pp
The following errors can occur for an
.Em NFS
filesystem mount:
.Bl -tag -width [ETIMEDOUT]
.It Bq Er ETIMEDOUT
.Em NFS
timed out trying to contact the server.
.It Bq Er EFAULT
Some part of the information described by nfs_args
points outside the process's allocated address space.
.El
.Pp
The following errors can occur for a
.Em mfs
filesystem mount:
.Bl -tag -width [EMFILE]
.It Bq Er EMFILE
No space remains in the mount table.
.It Bq Er EINVAL
The super block for the filesystem had a bad magic
number or an out of range block size.
.It Bq Er ENOMEM
Not enough memory was available to read the cylinder
group information for the filesystem.
.It Bq Er EIO
A paging error occurred while reading the super block or
cylinder group information.
.It Bq Er EFAULT
.Em Name
points outside the process's allocated address space.
.El
.Pp
.Fn unmount
may fail with one of the following errors:
.Bl -tag -width [ENAMETOOLONG]
.It Bq Er EPERM
The caller is not the superuser.
.It Bq Er ENOTDIR
A component of the path is not a directory.
.It Bq Er EINVAL
An argument given was invalid.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Dv NAME_MAX
characters, or an entire pathname (including the terminating NUL)
exceeded
.Dv PATH_MAX
bytes.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EINVAL
The requested directory is not in the mount table.
.It Bq Er EBUSY
A process is holding a reference to a file located
on the filesystem.
.It Bq Er EIO
An I/O error occurred while writing cached filesystem information.
.It Bq Er EFAULT
.Fa dir
points outside the process's allocated address space.
.El
.Sh SEE ALSO
.Xr statfs 2 ,
.Xr mount 8 ,
.Xr mount_mfs 8 ,
.Xr umount 8
.Sh HISTORY
The
.Fn mount
and
.Fn unmount
system calls first appeared in
.At v1 .
The
.Fa flags
argument is supported by
.Fn mount
since
.At v5
and by
.Fn unmount
since
.Bx 4.3 Reno .
The current calling convention involving
.Fa type
and
.Fa data
arguments was introduced by
.Bx 4.3 Reno
as well.
.Sh BUGS
Some of the error codes need translation to more obvious messages.