sudo

sudo

sudo in a terminal
Developer(s)	Todd C. Miller
Stable release	1.7.2p6 / April 9, 2010; 10 months ago (2010-04-09)
Operating system	Unix-like
Type	Privilege authorization
License	ISC-style[1]
Website	www.sudo.ws

The sudo ("su do", pronounced /ˈsuːduː/^[2], though /ˈsuːdoʊ/ is also common, (think "pseudo"), as is /ˌɛsˌjuːˈduː/) command is a program for some Unix and Unix-like computer operating systems that allows users to run programs with the security privileges of another user (normally the superuser, or root). It is an abbreviation for "substitute user do" (as in, do a command with another user's privileges). By default, sudo will prompt for a user password but it may be configured to require the root password, or require it only once per pseudo terminal, or no password at all.^[3] Sudo is able to log each command run and in some cases has completely supplanted the superuser login for administrative tasks, most notably in Ubuntu Linux and Apple's Mac OS X.^[4][5]

The program was originally written by Bob Coggeshall and Cliff Spencer "around 1980" at the Department of Computer Science at SUNY/Buffalo. The current version is under active development and is maintained by OpenBSD developer Todd C Miller and distributed under a BSD-style license.^[6]

Recent fears that Microsoft had patented the sudo command^[7] were found to be "overblown" with the claims being narrowly framed to a particular GUI rather than the sudo concept.^[8]

Design

Before running a command with sudo, users typically supply their password. Once authenticated, and if the /etc/sudoers configuration file permits the user access, then the command is run. There exist several graphical frontends for use in a GUI environment, notably kdesudo, and gksudo; Mac OS X also has Authorization Services.^[9] By default the user's password can be retained through a grace period, allowing the user to execute several successive commands as root without having to provide the password again.

The following is an example where the user is denied access:

snorri@rimu:~$ sudo emacs /etc/resolv.conf

 We assume you have received the usual lecture from the local System
 Administrator. It usually boils down to these three things:

 #1) Respect the privacy of others.
 #2) Think before you type.
 #3) With great power comes great responsibility.

 Password:
 snorri is not in the sudoers file. This incident will be reported.
 snorri@rimu:~$

Below is the log of this failed attempt, then a later successful one, after snorri has been added to /etc/sudoers:

snorri@rimu:~$ sudo tail /var/log/auth.log
 Aug 5 06:00:28 localhost sudo: snorri : user NOT in sudoers ; TTY=pts/1 ; PWD =/home/snorri ; USER=root ; 
      COMMAND=/usr/bin/emacs /etc/resolv.conf
 Aug 5 06:01:15 localhost su[15573]: (pam_unix) session opened for user root by snorri(uid=1000)
 Aug 5 06:02:09 localhost sudo: snorri : TTY=pts/1 ; PWD=/home/snorri ; USER=root ; COMMAND=/usr/bin/emacs /etc/resolv.conf
 Aug 5 06:02:49 localhost sudo: snorri : TTY=pts/1 ; PWD=/home/snorri ; USER=root ; COMMAND=/usr/bin/tail /var/log/auth.log

Runas, su and sudo

Windows has a command called runas. It has similar functionality, but neither runas nor UAC is sudo; rather, they impersonate another user rather than add privileges.

Runas and su:

• do not allow authorized users to launch processes with elevated privileges using their own passphrase.
• do not preserve the user's profile and ownership of created objects.

The runas command is (more or less) equivalent to Unix su, not sudo. The reason sudo is superior to su is that it allows privilege escalation based on the user’s own identity, and most importantly does not require use of a shared password. Using runas or su to access a privileged account requires distribution of a password to an admin-capable account, a security weakness that sudo does not have.

See also

• Comparison of privilege authorization features
• visudo, a vi-based program used to edit the /etc/sudoers file

References

External links

• Official website
• rootsh and sudosh, sudo wrappers for logging
• Sudo Fun, a brief guide to sudo on the Mac OS X