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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 ...
The Unix and Linux access rights flags setuid and setgid (short for set user identity and set group identity) [1] allow users to run an executable with the file system permissions of the executable's owner or group respectively and to change behaviour in directories. They are often used to allow users on a computer system to run programs with ...
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 ...
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 ...
Linux also has a file system user ID (fsuid) which is used explicitly for access control to the file system. It matches the euid unless explicitly set otherwise. It may be root's user ID only if ruid, suid, or euid is root. Whenever the euid is changed, the change is propagated to the fsuid.
Each program (technically called a process) has its own mask and is able to change its settings using a function call. When the process is a shell , the mask is set with the umask command. When a shell or process launches a new process, the child process inherits the mask from its parent process.
The current Linux manual pages for su define it as "substitute user", [9] making the correct meaning of sudo "substitute user, do", because sudo can run a command as other users as well. [10] [11] Unlike the similar command su, users must, by default, supply their own password for authentication, rather than the password of the target user.
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. Without the sticky bit set, any user with write and execute permissions for the directory can rename or delete contained files, regardless of the file ...