Content-type: text/html Man page of exportfs


Section: System Calls (2)
Index Return to Main Contents


exportfs - Exports an NFS file system  


#include <nfs/nfs.h>

exportfs(access, cookie, exdata) int access; int *cookie; struct exportfsdata *exdata;


The exportfs system call allows the specified local file system to be mounted remotely by an NFS client. This system call is usually called from mountd. The system call allows access to the kernels export data base. The method of access is specified by the access flag as follows:

#define EXPORTFS_CREATE 0x01 /* create a new export record */ #define EXPORTFS_REMOVE 0x02 /* remove an old export record */ #define EXPORTFS_READ 0x03 /* read an export record */

Each entry in the export data base has the following structure:

struct exportfsdata {
        dev_t   e_dev;     /* ID of device containing the directory */
        ino_t   e_ino;     /* File serial number */
        uint_t  e_gen;     /* File generation number */
        char e_path[MAXPATHLEN];  /* Name of the path to export */
        int  e_flags;             /* Export flags */
        uid_t e_rootmap;   /* Map root to this uid (either 0 or -2) */
        uid_t e_anon;      /* Map anonymous users to this uid */
        struct exportfsaddrlist e_rootaddrs;
                           /* List of hosts where root can be mapped
                            * to uid 0 */
        struct exportfsaddrlist e_writeaddrs;
                           /* List of hosts allowed write access to
                            * read mostly export */
        int     e_more;    /* Used in EXPORTFS_READ */ };

struct exportfsaddrlist {
        unsigned naddrs;
        struct sockaddr addrvec[EXMAXADDRS]; };

The e_path argument is a pointer to a null-terminated string containing the path name of the file system or directory being exported.

The e_dev, e_ino, and e_gen fields are inputs to the system call for creating an entry. They are returned when an entry is read.

Security on the exported file systems can be improved by setting the root mapped user ID in, e_rootmap and the anonymous user id in e_anon to user id -2. Setting the rootmap field to 0 specifies that all client superusers will be mapped to 0 and thus will have the same rights as the local superuser. Anonymous remote users are those without UNIX credentials and superusers on client systems. Setting anon to a user id other than -2 will map all anonymous users to that uid. Use of the rootmap field overrides values in e_anon for client superusers. Finally, to grant superuser privileges to only a select group of clients, set rootmap to -2 and use the e_rootaddrs structure to specify the list of privileged systems.

The export permissions flags are set in e_flags for the local file system path. The following flags are the only possible flags accepted by exportfs:

#define M_EXRDONLY /* export read-only */ #define M_EXRDMOSTLY /* export read-write to hosts in e_writeaddrs */

By default, exports are read-write. To export a filesystem or directory read-only, set the M_EXRDONLY flag. To export a filesystem or directory read-only to most clients and read-write to a select group, set the M_EXRDMOSTLY flag and include the list of clients in e_writeaddrs.

The e_more field is used in conjunction with the cookie parameter to sequentially read the kernel's export data base using EXPORTFS_READ. The contents of cookie should be set to zero to read the first record. After reading the record into exdata, the system call will set e_more to a non-zero value if there are more records to read and will update the value of cookie. If there are no more records in the data base, e_more will be zero after the system call completes.

The exportfs system call returns a value of 0 upon successful completion of an operation, and -1 upon failure.


Not superuser. Not enough memory in the system to service the request. Bad address for exdata or cookie. Access is EXPORTFS_CREATE or EXPORTFS_REMOVE and e_path does not exist, or access is EXPORTFS_REMOVE and e_path is not an exported path, or access is EXPORTFS_READ and there are no exportfsdata records to read. Access is EXPORTFS_CREATE and e_path is an NFS mounted directory. Only local directories can be exported. The exdata pointer is NULL, the cookie value is negative, or the access flag is invalid.


Files:  exports(4)

Daemons:  mountd(8)




This document was created by man2html, using the manual pages.
Time: 02:40:13 GMT, October 02, 2010