Su (Unix)

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The Unix command su, which stands for "substitute user" (or historically "superuser"), is used by a computer user to execute commands with the privileges of another user account. When executed it invokes a shell without changing the current working directory or the user environment. When the command is used without specifying the new user id as a command line argument, it defaults to using the superuser account (user id 0) of the system. The command su, including the Unix permissions system and the setuid system call, was part of Version 1 Unix. Encrypted passwords appeared in Version 3. The command is available as a separate package for Microsoft Windows as part of the UnxUtils collection of native Win32 ports of common GNU Unix-like utilities. When run from the command line, su asks for the target user's password, and if authenticated, grants the operator access to that account and the files and directories that account is permitted to access. When used with a hyphen (su -) it can be used to start a login shell. In this mode users can assume the user environment of the target user. The command sudo is related, and executes a command as another user but observes a set of constraints about which users can execute which commands as which other users (generally in a configuration file named /etc/sudoers, best editable by the command visudo).