--- name: "mount" section: "2" platform: "macos" package: "xnu" version: "12377.121.6" release: "macOS 26.5" platforms: ["linux", "freebsd", "macos"] url: "https://new.carta.tech/mount/2" --- # mount(2) mount or dismount a filesystem ## NAME **mount**, **fmount,** **unmount** **funmount** – mount or dismount a filesystem ## SYNOPSIS **#include \** **#include \** *int*\ **mount**(*const char \*type*, *const char \*dir*, *int flags*, *void \*data*); *int*\ **fmount**(*const char \*type*, *int fd*, *int flags*, *void \*data*); *int*\ **unmount**(*const char \*dir*, *int flags*); *int*\ **funmount**(*int fd*, *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\_NODEV Do not interpret special files on the filesystem. - MNT\_UNION Union with underlying filesystem instead of obscuring it. - MNT\_SYNCHRONOUS All I/O to the filesystem should be done synchronously. - MNT\_CPROTECT Enable data protection on the filesystem if the filesystem is configured for it. 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, most 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. *Data* is a pointer to a structure that contains the type specific arguments to mount. The format for these argument structures is described in the manual page for each filesystem. The **fmount**() function call is equivalent to the **mount**() function call, except in the use of the second argument. It takes an open file descriptor representing the mount point instead of the string literal containing full path to the mount point in the filesystem hierarchy. The **unmount**() 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 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. The **funmount**() function call is equivalent to the **unmount**() function call, except in the use of the first argument. It takes an open file descriptor representing the mount point instead of the string literal containing full path to the mount point in the filesystem hierarchy. ## RETURN VALUES The **mount**() and **fmount**() return the value 0 if the mount was successful, otherwise -1 is returned and the variable *errno* is set to indicate the error. **unmount**() and **funmount**() returns the value 0 if the unmount succeeded; otherwise -1 is returned and the variable *errno* is set to indicate the error. ## ERRORS **mount**() and **fmount**() will fail when one of the following occurs: - \[EPERM\] The caller is not the super-user, and the device-node and the mountpoint do not have adequate ownership and permissions. - \[ENAMETOOLONG\] A component of a pathname exceeded {NAME\_MAX} characters, or an entire path name exceeded {PATH\_MAX} 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. - \[EINVAL\] A pathname contains a character with the high-order bit set. - \[EBUSY\] Another process currently holds a reference to *dir*. - \[EFAULT\] *Dir* points outside the process's allocated address space. - \[ENOTSUP\] The operation is not supported for the '/dev/fd' filesystem. **unmount**() and **funmount**() may fail with one of the following errors: - \[EPERM\] The caller is not the super-user, and the **mount()** was not done by the user. - \[EPERM\] A system policy denied the operation. - \[ENOTDIR\] 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 {NAME\_MAX} characters, or an entire path name exceeded {PATH\_MAX} characters. - \[ELOOP\] Too many symbolic links were encountered in translating the pathname. - \[ENOENT\] A component of *dir* does not exist. - \[EINVAL\] 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. - \[ENOTSUP\] The operation is not supported for the '/dev/fd' filesystem. ## SEE ALSO [mount(8)](/mount/8.md), unmount(8), [open(2)](/open/2.md) ## BUGS Some of the error codes need translation to more obvious messages. ## HISTORY **mount**() and **unmount**() function calls appeared in Version 6 AT&T UNIX. **fmount**() function call first appeared in macOS version 10.13. **funmount**() function call first appeared in macOS version 16.