sudo is a program for Unix-like computer operating systems that allows users to run programs with the security privileges of another user, by default the superuser. It originally stood for "superuser do" as the older versions of sudo were designed to run commands only as the superuser. However, the later versions added support for running commands not only as the superuser but also as other users, and thus it is also commonly expanded as "substitute user do". Although the latter case reflects its current functionality more accurately, sudo is still often called "superuser do" since it is so often used for administrative tasks. Unlike the similar command su, users must, by default, supply their own password for authentication, rather than the password of the target user. After authentication, and if the configuration file, which is typically located at /etc/sudoers, permits the user access, the system invokes the requested command. The configuration file offers detailed access permissions, including enabling commands only from the invoking terminal; requiring a password per user or group; requiring re-entry of a password every time or never requiring a password at all for a particular command line. It can also be configured to permit passing arguments or multiple commands.
Unlike the command su, users supply their personal password to sudo if necessary. After authentication, and if the configuration file permits the user access, the system invokes the requested command. sudo retains the user's invocation rights through a grace period per pseudo terminal by default, allowing the user to execute several successive commands as the requested user without having to provide a password again. sudo may be configured to log each command run. When a user attempts to invoke sudo without being listed in the configuration file, an exception indication is presented to the user indicating that the attempt has been recorded. The root user will be alerted via mail and an entry is recorded in the system.
Configuration
The file /etc/sudoers contains a list of users or user groups with permission to execute a subset of commands while having the privileges of the root user or another specified user. The program may be configured to require a password.
Impact
In some system distributions, sudo has largely supplanted the default use of a distinct superuser login for administrative tasks, most notably in some Linux distributions as well as Apple's macOS. This allows for more secure logging of admin commands and prevents some exploits.
visudo is a command-line utility that allows editing the sudo configuration file in a fail-safe manner. It prevents multiple simultaneous edits with locks and performs sanity and syntax checks. The program runas provides similar functionality in Microsoft Windows, but it cannot pass current directories, environment variables or long command lines to the child. And while it supports running the child as another user, it does not support simple elevation. A true su and sudo for Windows that can pass all of that state information and start the child either elevated or as another user is included with Hamilton C shell. Graphical user interfaces exist for sudo – notably gksudo – but are deprecated in Debian and no longer included in Ubuntu. Other user interfaces are not directly built on sudo, but provide similar temporary privilege elevation for administrative purposes, such as User Account Control in Microsoft Windows and Mac OS X Authorization Services. doas, available since OpenBSD 5.8, has been written in order to replace sudo in the OpenBSD base system, with the latter still being made available as a port.
