Operations on UNIX file systems
Most file systems have methods to assign permissions or access rights to specific users and groups of users. These systems control the ability of the users to view or make changes to the contents of the filesystem.
Operating system variations
Unix-like and otherwise POSIX-compliant systems, including Linux-based systems and all Mac OS X versions, have a simple system for managing individual file permissions, which in this article are called "traditional Unix permissions". Most of these systems also support some kind of access control lists, either proprietary (old HP-UX ACLs, for example), or POSIX.1e ACLs, based on an early POSIX draft that was abandoned, or NFSv4 ACLs, which are part of the NFSv4 standard.
Microsoft and IBM DOS variants (including MS-DOS, PC DOS, Windows 95, Windows 98, Windows 98 SE, and Windows Me) do not have permissions, only file attributes. There is a read-only attribute (R), which can be set or unset on a file by any user or program, and therefore does not prevent him/her from changing/deleting the file. There is no permission in these systems which would prevent a user from reading a file.
Other MS-DOS/PC DOS-compatible operating systems such as DR DOS 3.31 and higher, PalmDOS, Novell DOS, and OpenDOS, FlexOS, 4680 OS, 4690 OS, Concurrent DOS, Multiuser DOS, Datapac System Manager and IMS REAL/32 support read/write/execute/delete file/directory access permissions on FAT volumes. With the exception of FlexOS, 4680 OS, and 4690 OS all these operating systems also support individual file/directory passwords. All operating systems except for DR DOS, PalmDOS, Novell DOS and OpenDOS also support three independent file/directory ownership classes world/group/owner, whereas the single-user operating systems DR DOS 6.0 and higher, PalmDOS, Novell DOS and OpenDOS only support them with an optional multi-user security module loaded.
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