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.

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 supported by the current running kernel obtained using sysctl(8) to obtain the node vfs.generic.fstypes. data is a pointer to a structure that contains the type specific arguments to mount. Some of 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 */ 
};

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 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

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:

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

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

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

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

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

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.

Manual browser: mount(2)