sudo(8) MAINTENANCE COMMANDS sudo(8)
NNAAMMEE
sudo - execute a command as another user
SSYYNNOOPPSSIISS
ssuuddoo --VV | --hh | --ll | --LL | --vv | --kk | --KK | --ss | [ --HH ] [--SS ]
[ --bb ] | [ --pp prompt ] [ --cc class|- ] [ --aa auth_type ] [
--uu username/#uid ] command
DDEESSCCRRIIPPTTIIOONN
ssuuddoo allows a permitted user to execute a command as the
superuser or another user, as specified in the sudoers
file. The real and effective uid and gid are set to match
those of the target user as specified in the passwd file
(the group vector is also initialized when the target user
is not root). By default, ssuuddoo requires that users
authenticate themselves with a password (NOTE: this is the
user's password, not the root password). Once a user has
been authenticated, a timestamp is updated and the user
may then use sudo without a password for a short period of
time (five minutes by default).
ssuuddoo determines who is an authorized user by consulting
the file /etc/sudoers. By giving ssuuddoo the -v flag a user
can update the time stamp without running a command. The
password prompt itself will also time out if the user's
password is not entered with N minutes (again, this is
defined at configure time and defaults to 5 minutes).
If a user that is not listed in the sudoers file tries to
run a command via ssuuddoo, mail is sent to the proper
authorities, as defined at configure time (defaults to
root). Note that the mail will not be sent if an
unauthorized user tries to run sudo with the -l or -v
flags. This allows users to determine for themselves
whether or not they are allowed to use ssuuddoo.
ssuuddoo can log both successful and unsuccessful attempts (as
well as errors) to syslog(3), a log file, or both. By
default ssuuddoo will log via syslog(3) but this is changeable
at configure time.
OOPPTTIIOONNSS
ssuuddoo accepts the following command line options:
-V The -V (version) option causes ssuuddoo to print the
version number and exit.
-l The -l (list) option will list out the allowed (and
forbidden) commands for the user on the current host.
-L The -L (list defaults) option will list out the
parameters that may be set in a Defaults line along
with a short description for each. This option is
useful in conjunction with grep(1).
26/Mar/2000 1.6.3 1
sudo(8) MAINTENANCE COMMANDS sudo(8)
-h The -h (help) option causes ssuuddoo to print a usage
message and exit.
-v If given the -v (validate) option, ssuuddoo will update
the user's timestamp, prompting for the user's
password if necessary. This extends the ssuuddoo timeout
to for another N minutes (where N is defined at
installation time and defaults to 5 minutes) but does
not run a command.
-k The -k (kill) option to ssuuddoo invalidates the user's
timestamp by setting the time on it to the epoch. The
next time ssuuddoo is run a password will be required.
This option does not require a password and was added
to allow a user to revoke ssuuddoo permissions from a
.logout file.
-K The -K (sure kill) option to ssuuddoo removes the user's
timestamp entirely. This option does not require a
password.
-b The -b (background) option tells ssuuddoo to run the given
command in the background. Note that if you use the
-b option you cannot use shell job control to
manipulate the command.
-p The -p (prompt) option allows you to override the
default password prompt and use a custom one. If the
password prompt contains the %u escape, %u will be
replaced with the user's login name. Similarly, %h
will be replaced with the local hostname.
-c The --cc (class) option causes ssuuddoo to run the specified
command with resources limited by the specified login
class. The class argument can be either a class name
as defined in /etc/login.conf, or a single '-'
character. Specifying a class of - indicates that the
command should be run restricted by the default login
capabilities for the user the command is run as. If
the class argument specifies an existing user class,
the command must be run as root, or the ssuuddoo command
must be run from a shell that is already root. This
option is only available on systems with BSD login
classes where ssuuddoo has been configured with the
--with-logincap option.
-a The --aa (authentication type) option causes ssuuddoo to use
the specified authentication type when validating the
user, as allowed by /etc/login.conf. The system
administrator may specify a list of sudo-specific
authentication methods by adding an "auth-sudo" entry
in /etc/login.conf. This option is only available on
systems that support BSD authentication where ssuuddoo has
been configured with the --with-bsdauth option.
26/Mar/2000 1.6.3 2
sudo(8) MAINTENANCE COMMANDS sudo(8)
-u The -u (user) option causes ssuuddoo to run the specified
command as a user other than root. To specify a uid
instead of a username, use "#uid".
-s The -s (shell) option runs the shell specified by the
SHELL environment variable if it is set or the shell
as specified in passwd(5).
-H The -H (HOME) option sets the HOME environment
variable to the homedir of the target user (root by
default) as specified in passwd(5). By default, ssuuddoo
does not modify HOME.
-S The -S (stdin) option causes ssuuddoo to read the password
from standard input instead of the terminal device.
-- The -- flag indicates that ssuuddoo should stop processing
command line arguments. It is most useful in
conjunction with the -s flag.
RREETTUURRNN VVAALLUUEESS
ssuuddoo quits with an exit value of 1 if there is a
configuration/permission problem or if ssuuddoo cannot execute
the given command. In the latter case the error string is
printed to stderr. If ssuuddoo cannot stat(2) one or more
entries in the user's PATH an error is printed on stderr.
(If the directory does not exist or if it is not really a
directory, the entry is ignored and no error is printed.)
This should not happen under normal circumstances. The
most common reason for stat(2) to return "permission
denied" is if you are running an automounter and one of
the directories in your PATH is on a machine that is
currently unreachable.
SSEECCUURRIITTYY NNOOTTEESS
ssuuddoo tries to be safe when executing external commands.
Variables that control how dynamic loading and binding is
done can be used to subvert the program that ssuuddoo runs.
To combat this the LD_*, _RLD_*, SHLIB_PATH (HP-UX only),
and LIBPATH (AIX only) environment variables are removed
from the environment passed on to all commands executed.
ssuuddoo will also remove the IFS, ENV, BASH_ENV, KRB_CONF,
KRB5_CONFIG, LOCALDOMAIN, RES_OPTIONS and HOSTALIASES
variables as they too can pose a threat.
To prevent command spoofing, ssuuddoo checks "." and "" (both
denoting current directory) last when searching for a
command in the user's PATH (if one or both are in the
PATH). Note, however, that the actual PATH environment
variable is not modified and is passed unchanged to the
program that ssuuddoo executes.
For security reasons, if your OS supports shared libraries
and does not disable user-defined library search paths for
26/Mar/2000 1.6.3 3
sudo(8) MAINTENANCE COMMANDS sudo(8)
setuid programs (most do), you should either use a linker
option that disables this behavior or link ssuuddoo
statically.
ssuuddoo will check the ownership of its timestamp directory
(/var/run/sudo by default) and ignore the directory's
contents if it is not owned by root and only writable by
root. On systems that allow non-root users to give away
files via chown(2), if the timestamp directory is located
in a directory writable by anyone (e.g.: /tmp), it is
possible for a user to create the timestamp directory
before ssuuddoo is run. However, because ssuuddoo checks the
ownership and mode of the directory and its contents, the
only damage that can be done is to "hide" files by putting
them in the timestamp dir. This is unlikely to happen
since once the timestamp dir is owned by root and
inaccessible by any other user the user placing files
there would be unable to get them back out. To get around
this issue you can use a directory that is not world-
writable for the timestamps (/var/adm/sudo for instance)
or create /var/run/sudo with the appropriate owner (root)
and permissions (0700) in the system startup files.
ssuuddoo will not honor timestamps set far in the future.
Timestamps with a date greater than current_time + 2 *
TIMEOUT will be ignored and sudo will log and complain.
This is done to keep a user from creating his/her own
timestamp with a bogus date on system that allow users to
give away files.
EEXXAAMMPPLLEESS
Note: the following examples assume suitable sudoers(5)
entries.
To get a file listing of an unreadable directory:
% sudo ls /usr/local/protected
To list the home directory of user yazza on a machine
where the filesystem holding ~yazza is not exported as
root:
% sudo -u yazza ls ~yazza
To edit the index.html file as user www:
% sudo -u www vi ~www/htdocs/index.html
To shutdown a machine:
% sudo shutdown -r +15 "quick reboot"
To make a usage listing of the directories in the /home
partition. Note that this runs the commands in a sub-
26/Mar/2000 1.6.3 4
sudo(8) MAINTENANCE COMMANDS sudo(8)
shell to make the cd and file redirection work.
% sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
EENNVVIIRROONNMMEENNTT
ssuuddoo utilizes the following environment variables:
PATH Set to a sane value if SECURE_PATH is set
SHELL Used to determine shell to run with -s option
USER Set to the target user (root unless the -u option
is specified)
HOME In -s or -H mode (or if sudo was configured with
the --enable-shell-sets-home option), set to
homedir of the target user.
SUDO_PROMPT Used as the default password prompt
SUDO_COMMAND Set to the command run by sudo
SUDO_USER Set to the login of the user who invoked sudo
SUDO_UID Set to the uid of the user who invoked sudo
SUDO_GID Set to the gid of the user who invoked sudo
SUDO_PS1 If set, PS1 will be set to its value
FFIILLEESS
/etc/sudoers List of who can run what
/var/run/sudo Directory containing timestamps
AAUUTTHHOORRSS
Many people have worked on ssuuddoo over the years. This
version consists of code written primarily by:
Todd Miller
Chris Jepeway
See the HISTORY file in the ssuuddoo distribution for a short
history of ssuuddoo.
BBUUGGSS
If you feel you have found a bug in sudo, please submit a
bug report at http://www.courtesan.com/sudo/bugs/
DDIISSCCLLAAIIMMEERR
SSuuddoo is provided ``AS IS'' and any express or implied
warranties, including, but not limited to, the implied
warranties of merchantability and fitness for a particular
purpose are disclaimed. See the LICENSE file distributed
with ssuuddoo for complete details.
CCAAVVEEAATTSS
There is no easy way to prevent a user from gaining a root
shell if that user has access to commands allowing shell
escapes.
26/Mar/2000 1.6.3 5
sudo(8) MAINTENANCE COMMANDS sudo(8)
If users have sudo ALL there is nothing to prevent them
from creating their own program that gives them a root
shell regardless of any '!' elements in the user
specification.
Running shell scripts via ssuuddoo can expose the same kernel
bugs that make setuid shell scripts unsafe on some
operating systems (if your OS supports the /dev/fd/
directory, setuid shell scripts are generally safe).
SSEEEE AALLSSOO
sudoers(5), visudo(8), su(1).
26/Mar/2000 1.6.3 6