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In Unix and Unix-like operating systems, chmod is the command and system call used to change the access permissions and the special mode flags (the setuid, setgid, and sticky flags) of file system objects (files and directories). Collectively these were originally called its modes, [1] and the name chmod was chosen as an abbreviation of change ...
Distinct permissions apply to the owner. Files and directories are assigned a group, which define the file's group class. Distinct permissions apply to members of the file's group. The owner may be a member of the file's group. Users who are not the owner, nor a member of the group, comprise a file's others class. Distinct permissions apply to ...
The command chown / ˈ tʃ oʊ n /, an abbreviation of change owner, is used on Unix and Unix-like operating systems to change the owner of file system files and directories. Unprivileged (regular) users who wish to change the group membership of a file that they own may use chgrp. The ownership of any file in the system may only be altered by ...
The most common modern use of the sticky bit is on directories residing within filesystems for Unix-like operating systems. When a directory's sticky bit is set, the filesystem treats the files in such directories in a special way so only the file's owner, the directory's owner, or root can rename or delete the file.
In Unix and Unix-like systems, including POSIX-conforming systems, each file has a 'mode' containing 9 bit flags controlling read, write and execute permission for each of the file's owner, group and all other users (see File-system permissions §Traditional Unix permissions for more details) plus the setuid and setgid bit flags and a 'sticky' bit flag.
The setuid and setgid bits are normally represented as the values 4 for setuid and 2 for setgid in the high-order octal digit of the file mode. For example, 6711 has both the setuid and setgid bits (4 + 2 = 6) set, and also the file read/write/executable for the owner (7), and executable by the group (first 1) and others (second 1).
The mask is generally only applied to functions that create a new file; however, there are exceptions. For example, when using UNIX and GNU versions of chmod to set the permissions of a file, and symbolic notation is used, and no user is specified, then the mask is applied to the requested permissions before they are applied to the file. For ...
chmod: ATTRIB, PROT, and the chmod UNIX command are all somewhat different in their semantics. UNIX/Linux is multi-user and each user can control read, write, and execute permissions on his or her own files and directories. MS-DOS is single user and the file attributes for "read-only," "hidden," and "system" are advisory in nature. TRSDOS was ...