The file /etc/suauth is referenced whenever the su command is
called. It can change the behaviour of the su command, based
1) the user su is targeting
2) the user executing the su command (or any groups he might be a
The file is formatted like this, with lines starting with a #
being treated as comment lines and ignored;
Where to-id is either the word ALL, a list of usernames delimited
by "," or the words ALL EXCEPT followed by a list of usernames
delimited by ",".
from-id is formatted the same as to-id except the extra word
GROUP is recognized. ALL EXCEPT GROUP is perfectly valid too.
Following GROUP appears one or more group names, delimited by
",". It is not sufficient to have primary group id of the
relevant group, an entry in /etc/group(5) is necessary.
Action can be one only of the following currently supported
The attempt to su is stopped before a password is even asked
The attempt to su is automatically successful; no password is
For the su command to be successful, the user must enter his
or her own password. They are told this.
Note there are three separate fields delimited by a colon. No
whitespace must surround this colon. Also note that the file is
examined sequentially line by line, and the first applicable rule
is used without examining the file further. This makes it
possible for a system administrator to exercise as fine control
as he or she wishes.
# sample /etc/suauth file
# A couple of privileged usernames may
# su to root with their own password.
# Anyone else may not su to root unless in
# group wheel. This is how BSD does things.
root:ALL EXCEPT GROUP wheel:DENY
# Perhaps terry and birddog are accounts
# owned by the same person.
# Access can be arranged between them
# with no password.
There could be plenty lurking. The file parser is particularly
unforgiving about syntax errors, expecting no spurious whitespace
(apart from beginning and end of lines), and a specific token
delimiting different things.
This page is part of the shadow-utils (utilities for managing
accounts and shadow password files) project. Information about
the project can be found at
⟨https://github.com/shadow-maint/shadow⟩. If you have a bug
report for this manual page, send it to
firstname.lastname@example.org. This page was obtained
from the project's upstream Git repository
⟨https://github.com/shadow-maint/shadow⟩ on 2021-08-27. (At that
time, the date of the most recent commit that was found in the
repository was 2021-08-14.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
shadow-utils 4.8.1 08/27/2021 SUAUTH(5)