Depending on the file system type, other options may be recognized or required; for example, most disk-based file systems require a "from" option containing the pathname of a special device in addition to the options listed above.
By default only the super-user may call the mount system call. This restriction can be removed by setting the vfs.usermountsysctl(8) variable to a non-zero value.
The following flags may be specified to suppress default semantics which affect file system access.
MNT_RDONLY
The file system should be treated as read-only; even the super-user may not write on it. Specifying MNT_UPDATE without this option will upgrade a read-only file system to read/write.
MNT_NOEXEC
Do not allow files to be executed from the file system.
MNT_NOSUID
Do not honor setuid or setgid bits on files when executing them. This flag is set automatically when the caller is not the super-user.
MNT_NOATIME
Disable update of file access times.
MNT_SNAPSHOT
Create a snapshot of the file system. This is currently only supported on UFS2 file systems, see mksnap_ffs(8) for more information.
MNT_SUIDDIR
Directories with the SUID bit set chown new files to their own owner. This flag requires the SUIDDIR option to have been compiled into the kernel to have any effect. See the mount(8) and chmod(2) pages for more information.
MNT_SYNCHRONOUS
All I/O to the file system should be done synchronously.
MNT_ASYNC
All I/O to the file system should be done asynchronously.
MNT_FORCE
Force a read-write mount even if the file system appears to be unclean. Dangerous. Together with MNT_UPDATE and MNT_RDONLY, specify that the file system is to be forcibly downgraded to a read-only mount even if some files are open for writing.
MNT_NOCLUSTERR
Disable read clustering.
MNT_NOCLUSTERW
Disable write clustering.
The flag MNT_UPDATE indicates that the mount command is being applied to an already mounted file system. This allows the mount flags to be changed without requiring that the file system be unmounted and remounted. Some file systems may not allow all flags to be changed. For example, many file systems 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 file system.
The type argument names the file system. The types of file systems known to the system can be obtained with lsvfs(1).
The data argument 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 file system. By convention file system manual pages are named by prefixing ‘‘mount_’’ to the name of the file system as returned by lsvfs(1). Thus the NFS file system is described by the mount_nfs(8) manual page. It should be noted that a manual page for default file systems, known as UFS and UFS2, does not exist.
The unmount system call disassociates the file system from the specified mount point dir.
The flags argument may include 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.
If the MNT_BYFSID flag is specified, dir should instead be a file system ID encoded as "FSID: val0: val1", where val0 and val1 are the contents of the .Vt fsid_t val[] array in decimal. The file system that has the specified file system ID will be unmounted.
