Su (Unix)

The command {{mono|su}}, including the Unix permissions system and the setuid system call, was part of Version 1 Unix. Encrypted passwords appeared in Version 3.{{cite tech report

| first1 = M. D.

| last1 = McIlroy

| authorlink1 = Doug McIlroy

| year = 1987

| url = https://www.cs.dartmouth.edu/~doug/reader.pdf

| title = A Research Unix reader: offticles annotated excerpts from the Programmer's Manual, 1971–1986

| series = CSTR

| number = 139

| institution = Bell Labs}} 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.{{Cite web|url=http://unxutils.sourceforge.net/|title=Native Win32 ports of some GNU utilities|website=unxutils.sourceforge.net}}

The {{mono|su}} command was removed from GNU coreutils as of release 8.18 (2012-08-12){{Cite web|url=https://github.com/coreutils/coreutils/blob/master/NEWS|title=NEWS|website=GitHub |date=17 September 2022 }} and is currently included in the util-linux package.

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.

john@localhost:~$ su jane

Password:

jane@localhost:/home/john$ exit

logout

john@localhost:~$

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.

john@localhost:~$ su - jane

Password:

jane@localhost:~$

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, and only allow members to become root with {{mono|su}}.{{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}} 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.{{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}}

• Unix security
• List of Unix commands
• Comparison of privilege authorization features

• {{Cite web |date=2013-01-14 |title=From Novice to Master, and Back Again |url=https://blog.djmnet.org/2013/01/14/from-novice-to-master-and-back-again/ |access-date=2022-08-10 |website=D-Mac's Stuff |language=en}}

{{Reflist}}

• [https://web.archive.org/web/20131210155635/http://www.gnu.org/software/coreutils/manual/html_node/su-invocation.html su] – manual pages from GNU coreutils.
• {{man|1|su|die.net}}
• {{man|1|su|FreeBSD}}
• {{man|8|su|Solaris}}
• [http://www.linfo.org/su.html The su command] – by The Linux Information Project (LINFO) ({{Webarchive |url=https://web.archive.org/web/20211020082958/http://www.linfo.org/su.html |date=20 October 2021}})

{{Unix commands}}

Category:Unix user management and support-related utilities

Category:System administration

{{unix-stub}}