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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 ...
Most file systems include attributes of files and directories that control the ability of users to read, change, navigate, and execute the contents of the file system. In some cases, menu options or functions may be made visible or hidden depending on a user's permission level; this kind of user interface is referred to as permission-driven.
chmod: Changes the permissions of a file or directory cp: Copies a file or directory dd: Copies and converts a file df: Shows disk free space on file systems dir: Is exactly like "ls -C -b". (Files are by default listed in columns and sorted vertically.) dircolors: Set up color for ls: install: Copies files and set attributes ln: Creates a link ...
Most implementations have a symbolic representation of these bits; in the previous example, this could be u=rwx,go=x,ug+s. Typically, chmod does not have a recursive mode restricted to directories, so modifying an existing directory tree must be done manually, with a command such as find /path/to/directory-type d-exec chmod g+s '{}' '\'.
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.
The maximum size of a volume that the file system specification can handle. This may differ from the maximum size an operating system supports using a given implementation of the file system. Name The full, non abbreviated, name of the file system itself. Named streams Determines if the file systems supports multiple data streams.
Operating systems, like all software, may contain bugs in need of fixing or may be enhanced with the addition of new features; many UNIX systems come with a package manager for this. Patching the operating system in a secure manner requires that the software come from a trustworthy source and not have been altered since it was packaged.
The operating system evolved in a relatively small computer-center environment, where security was not an issue. It eventually grew to serve hundreds of users from different organizations. At first, developers made creation modes for key files more restrictive, especially for cases of actual security breaches, but this was not a general solution.