=cut Copyright (c) 1994-1996,1998-2002 Todd C. Miller <Todd.Miller@courtesan.com> All rights reserved. Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met: 1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer. 2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution. 3. The name of the author may not be used to endorse or promote products derived from this software without specific prior written permission from the author. 4. Products derived from this software may not be called "Sudo" nor may "Sudo" appear in their names without specific prior written permission from the author. THIS SOFTWARE 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. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. $Sudo: sudo.pod,v 1.51 2002/01/12 22:55:01 millert Exp $ =pod =head1 NAME sudo - execute a command as another user =head1 SYNOPSIS B<sudo> B<-V> | B<-h> | B<-l> | B<-L> | B<-v> | B<-k> | B<-K> | B<-s> | [ B<-H> ] [B<-P> ] [B<-S> ] [ B<-b> ] | [ B<-p> I<prompt> ] [ B<-c> I<class>|I<-> ] [ B<-a> I<auth_type> ] [ B<-u> I<username>|I<#uid> ] I<command> =head1 DESCRIPTION B<sudo> allows a permitted user to execute a I<command> as the superuser or another user, as specified in the I<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, B<sudo> requires that users authenticate themselves with a password (NOTE: by default 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 (C<@timeout@> minutes unless overridden in I<sudoers>). B<sudo> determines who is an authorized user by consulting the file F<@sysconfdir@/sudoers>. By giving B<sudo> the B<-v> flag a user can update the time stamp without running a I<command.> The password prompt itself will also time out if the user's password is not entered within C<@password_timeout@> minutes (unless overridden via I<sudoers>). If a user who is not listed in the I<sudoers> file tries to run a command via B<sudo>, mail is sent to the proper authorities, as defined at configure time or the I<sudoers> file (defaults to root). Note that the mail will not be sent if an unauthorized user tries to run sudo with the B<-l> or B<-v> flags. This allows users to determine for themselves whether or not they are allowed to use B<sudo>. B<sudo> can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file, or both. By default B<sudo> will log via syslog(3) but this is changeable at configure time or via the I<sudoers> file. =head1 OPTIONS B<sudo> accepts the following command line options: =over 4 =item -V The B<-V> (I<version>) option causes B<sudo> to print the version number and exit. If the invoking user is already root the B<-V> option will print out a list of the defaults B<sudo> was compiled with as well as the machine's local network addresses. =item -l The B<-l> (I<list>) option will list out the allowed (and forbidden) commands for the user on the current host. =item -L The B<-L> (I<list> defaults) option will list out the parameters that may be set in a I<Defaults> line along with a short description for each. This option is useful in conjunction with grep(1). =item -h The B<-h> (I<help>) option causes B<sudo> to print a usage message and exit. =item -v If given the B<-v> (I<validate>) option, B<sudo> will update the user's timestamp, prompting for the user's password if necessary. This extends the B<sudo> timeout for another C<@timeout@> minutes (or whatever the timeout is set to in I<sudoers>) but does not run a command. =item -k The B<-k> (I<kill>) option to B<sudo> invalidates the user's timestamp by setting the time on it to the epoch. The next time B<sudo> is run a password will be required. This option does not require a password and was added to allow a user to revoke B<sudo> permissions from a .logout file. =item -K The B<-K> (sure I<kill>) option to B<sudo> removes the user's timestamp entirely. Likewise, this option does not require a password. =item -b The B<-b> (I<background>) option tells B<sudo> to run the given command in the background. Note that if you use the B<-b> option you cannot use shell job control to manipulate the process. =item -p The B<-p> (I<prompt>) option allows you to override the default password prompt and use a custom one. If the password prompt contains the C<%u> escape, C<%u> will be replaced with the user's login name. Similarly, C<%h> will be replaced with the local hostname. =item -c The B<-c> (I<class>) option causes B<sudo> to run the specified command with resources limited by the specified login class. The I<class> argument can be either a class name as defined in /etc/login.conf, or a single '-' character. Specifying a I<class> of C<-> indicates that the command should be run restricted by the default login capabilities for the user the command is run as. If the I<class> argument specifies an existing user class, the command must be run as root, or the B<sudo> command must be run from a shell that is already root. This option is only available on systems with BSD login classes where B<sudo> has been configured with the --with-logincap option. =item -a The B<-a> (I<authentication type>) option causes B<sudo> 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 B<sudo> has been configured with the --with-bsdauth option. =item -u The B<-u> (I<user>) option causes B<sudo> to run the specified command as a user other than I<root>. To specify a I<uid> instead of a I<username>, use I<#uid>. =item -s The B<-s> (I<shell>) option runs the shell specified by the I<SHELL> environment variable if it is set or the shell as specified in passwd(5). =item -H The B<-H> (I<HOME>) option sets the C<HOME> environment variable to the homedir of the target user (root by default) as specified in passwd(5). By default, B<sudo> does not modify C<HOME>. =item -P The B<-P> (I<preserve group vector>) option causes B<sudo> to preserve the user's group vector unaltered. By default, B<sudo> will initialize the group vector to the list of groups the target user is in. The real and effective group IDs, however, are still set to match the target user. =item -S The B<-S> (I<stdin>) option causes B<sudo> to read the password from standard input instead of the terminal device. =item -- The B<--> flag indicates that B<sudo> should stop processing command line arguments. It is most useful in conjunction with the B<-s> flag. =back =head1 RETURN VALUES Upon successful execution of a program, the return value from B<sudo> will simply be the return value of the program that was executed. Otherwise, B<sudo> quits with an exit value of 1 if there is a configuration/permission problem or if B<sudo> cannot execute the given command. In the latter case the error string is printed to stderr. If B<sudo> cannot stat(2) one or more entries in the user's C<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 C<PATH> is on a machine that is currently unreachable. =head1 SECURITY NOTES B<sudo> 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 B<sudo> runs. To combat this the C<LD_*>, C<_RLD_*>, C<SHLIB_PATH> (HP-UX only), and C<LIBPATH> (AIX only) environment variables are removed from the environment passed on to all commands executed. B<sudo> will also remove the C<IFS>, C<ENV>, C<BASH_ENV>, C<KRB_CONF>, C<KRBCONFDIR>, C<KRBTKFILE>, C<KRB5_CONFIG>, C<LOCALDOMAIN>, C<RES_OPTIONS>, C<HOSTALIASES>, C<NLSPATH>, C<PATH_LOCALE>, C<TERMINFO>, C<TERMINFO_DIRS> and C<TERMPATH> variables as they too can pose a threat. If the C<TERMCAP> variable is set and is a pathname, it too is ignored. Additionally, if the C<LC_*> or C<LANGUAGE> variables contain the C</> or C<%> characters, they are ignored. If B<sudo> has been compiled with SecurID support, the C<VAR_ACE>, C<USR_ACE> and C<DLC_ACE> variables are cleared as well. The list of environment variables that B<sudo> clears is contained in the output of C<sudo -V> when run as root. To prevent command spoofing, B<sudo> 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 C<PATH> environment variable is I<not> modified and is passed unchanged to the program that B<sudo> executes. For security reasons, if your OS supports shared libraries and does not disable user-defined library search paths for setuid programs (most do), you should either use a linker option that disables this behavior or link B<sudo> statically. B<sudo> will check the ownership of its timestamp directory (F<@timedir@> 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.: F</tmp>), it is possible for a user to create the timestamp directory before B<sudo> is run. However, because B<sudo> 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 (F</var/adm/sudo> for instance) or create F<@timedir@> with the appropriate owner (root) and permissions (0700) in the system startup files. B<sudo> will not honor timestamps set far in the future. Timestamps with a date greater than current_time + 2 * C<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 systems that allow users to give away files. Please note that B<sudo> will only log the command it explicitly runs. If a user runs a command such as C<sudo su> or C<sudo sh>, subsequent commands run from that shell will I<not> be logged, nor will B<sudo>'s access control affect them. The same is true for commands that offer shell escapes (including most editors). Because of this, care must be taken when giving users access to commands via B<sudo> to verify that the command does not inadvertantly give the user an effective root shell. =head1 EXAMPLES 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 F<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-shell to make the C<cd> and file redirection work. % sudo sh -c "cd /home ; du -s * | sort -rn > USAGE" =head1 ENVIRONMENT B<sudo> 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 =head1 FILES @sysconfdir@/sudoers List of who can run what @timedir@ Directory containing timestamps =head1 AUTHORS Many people have worked on B<sudo> over the years; this version consists of code written primarily by: Todd Miller Chris Jepeway See the HISTORY file in the B<sudo> distribution or visit http://www.sudo.ws/sudo/history.html for a short history of B<sudo>. =head1 BUGS If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/ =head1 DISCLAIMER B<Sudo> 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 B<sudo> for complete details. =head1 CAVEATS There is no easy way to prevent a user from gaining a root shell if that user has access to commands allowing shell escapes. If users have sudo C<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 B<sudo> 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). =head1 SEE ALSO stat(2), login_cap(3), sudoers(5), passwd(5), visudo(8), grep(1), su(1).