Editing Su (Unix) (section)

== Usage ==
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.

<syntaxhighlight lang="console">
john@localhost:~$ su jane
Password:
jane@localhost:/home/john$ exit
logout
john@localhost:~$ 
</syntaxhighlight>

When used with a [[hyphen]] ({{mono|su -}}) it can be used to start a login shell. In this mode users can assume the user environment of the target user.

<syntaxhighlight lang="console">
john@localhost:~$ su - jane
Password:
jane@localhost:~$
</syntaxhighlight>

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 {{mono|/etc/sudoers}}, best editable by the command {{mono|[[visudo]]}}). Unlike {{mono|su}}, {{mono|sudo}} authenticates users against their own password rather than that of the target user (to allow the delegation of specific commands to specific users on specific hosts without sharing passwords among them and while mitigating the risk of any unattended terminals).

Some [[Unix-like]] systems implement the user group ''[[Wheel (computing)|wheel]]'', and only allow members to become root with {{mono|su}}.<ref name=levi>{{cite book
 | title     = UNIX Administration: A Comprehensive Sourcebook for Effective Systems and Network Management
 | url     = https://archive.org/details/unixadministrati00levi_712
 | url-access = limited
 | first     = Bozidar
 | last      = Levi
 | publisher = CRC Press
 | year      = 2002
 | pages     = [https://archive.org/details/unixadministrati00levi_712/page/n217 207]
 | isbn      = 0-8493-1351-1}}</ref> This may or may not mitigate these security concerns, since an intruder might first simply break into one of those accounts. [[GNU]] {{mono|su}}, however, does not support the group ''wheel'' for philosophical reasons. [[Richard Stallman]] argues that because the group would prevent users from utilizing root passwords leaked to them, the group would allow existing admins to ride roughshod over ordinary users.<ref>{{cite web
 | url         = https://ftp.gnu.org/old-gnu/Manuals/coreutils-4.5.4/html_node/coreutils_149.html
 | title       = Why GNU su does not support the 'wheel' group
 | access-date = May 30, 2022
 | url-status  = live
 | archive-url  = https://web.archive.org/web/20210621182110/https://ftp.gnu.org/old-gnu/Manuals/coreutils-4.5.4/html_node/coreutils_149.html
 | archive-date = June 21, 2021}}</ref>