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sudo_root(8) [linux man page]

sudo_root(8)						      System Manager's Manual						      sudo_root(8)

NAME
sudo_root - How to run administrative commands SYNOPSIS
sudo command sudo -i INTRODUCTION
By default, the password for the user "root" (the system administrator) is locked. This means you cannot login as root or use su. Instead, the installer will set up sudo to allow the user that is created during install to run all administrative commands. This means that in the terminal you can use sudo for commands that require root privileges. All programs in the menu will use a graphical sudo to prompt for a password. When sudo asks for a password, it needs your password, this means that a root password is not needed. To run a command which requires root privileges in a terminal, simply prepend sudo in front of it. To get an interactive root shell, use sudo -i. ALLOWING OTHER USERS TO RUN SUDO
By default, only the user who installed the system is permitted to run sudo. To add more administrators, i. e. users who can run sudo, you have to add these users to the group 'admin' by doing one of the following steps: * In a shell, do sudo adduser username admin * Use the graphical "Users & Groups" program in the "System settings" menu to add the new user to the admin group. BENEFITS OF USING SUDO
The benefits of leaving root disabled by default include the following: * Users do not have to remember an extra password, which they are likely to forget. * The installer is able to ask fewer questions. * It avoids the "I can do anything" interactive login by default - you will be prompted for a password before major changes can happen, which should make you think about the consequences of what you are doing. * Sudo adds a log entry of the command(s) run (in /var/log/auth.log). * Every attacker trying to brute-force their way into your box will know it has an account named root and will try that first. What they do not know is what the usernames of your other users are. * Allows easy transfer for admin rights, in a short term or long term period, by adding and removing users from the admin group, while not compromising the root account. * sudo can be set up with a much more fine-grained security policy. * On systems with more than one administrator using sudo avoids sharing a password amongst them. DOWNSIDES OF USING SUDO
Although for desktops the benefits of using sudo are great, there are possible issues which need to be noted: * Redirecting the output of commands run with sudo can be confusing at first. For instance consider sudo ls > /root/somefile will not work since it is the shell that tries to write to that file. You can use ls | sudo tee /root/somefile to get the behaviour you want. * In a lot of office environments the ONLY local user on a system is root. All other users are imported using NSS techniques such as nss-ldap. To setup a workstation, or fix it, in the case of a network failure where nss-ldap is broken, root is required. This tends to leave the system unusable. An extra local user, or an enabled root password is needed here. GOING BACK TO A TRADITIONAL ROOT ACCOUNT
This is not recommended! To enable the root account (i.e. set a password) use: sudo passwd root Afterwards, edit the sudo configuration with sudo visudo and comment out the line %admin ALL=(ALL) ALL to disable sudo access to members of the admin group. SEE ALSO
sudo(8), https://wiki.ubuntu.com/RootSudo February 8, 2006 sudo_root(8)

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sudo(8) 						       MAINTENANCE COMMANDS							   sudo(8)

NAME
sudo - execute a command as another user SYNOPSIS
sudo -V | -h | -l | -L | -v | -k | -K | -s | [ -H ] [-P ] [-S ] [ -b ] | [ -p prompt ] [ -c class|- ] [ -a auth_type ] [ -u username|#uid ] command DESCRIPTION
sudo allows a permitted user to execute a command as the superuser or another user, as specified in the sudoers file. The real and effec- tive 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, 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 (5 minutes unless overridden in sudoers). sudo determines who is an authorized user by consulting the file /etc/sudoers. By giving sudo 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 within 5 minutes (unless overridden via sudoers). If a user who is not listed in the sudoers file tries to run a command via sudo, mail is sent to the proper authorities, as defined at con- figure time or the sudoers file (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 sudo. sudo can log both successful and unsuccessful attempts (as well as errors) to syslog(3), a log file, or both. By default sudo will log via syslog(3) but this is changeable at configure time or via the sudoers file. OPTIONS
sudo accepts the following command line options: -V The -V (version) option causes sudo to print the version number and exit. If the invoking user is already root the -V option will print out a list of the defaults sudo was compiled with as well as the machine's local network addresses. -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). -h The -h (help) option causes sudo to print a usage message and exit. -v If given the -v (validate) option, sudo will update the user's timestamp, prompting for the user's password if necessary. This extends the sudo timeout for another 5 minutes (or whatever the timeout is set to in sudoers) but does not run a command. -k The -k (kill) option to sudo invalidates the user's timestamp by setting the time on it to the epoch. The next time sudo is run a password will be required. This option does not require a password and was added to allow a user to revoke sudo permissions from a .logout file. -K The -K (sure kill) option to sudo removes the user's timestamp entirely. Likewise, this option does not require a password. -b The -b (background) option tells sudo 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 process. -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 -c (class) option causes sudo 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 com- mand 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 sudo command must be run from a shell that is already root. This option is only available on systems with BSD login classes where sudo has been configured with the --with-logincap option. -a The -a (authentication type) option causes 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 sudo has been configured with the --with-bsdauth option. -u The -u (user) option causes sudo 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, sudo does not modify HOME. -P The -P (preserve group vector) option causes sudo to preserve the user's group vector unaltered. By default, 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. -S The -S (stdin) option causes sudo to read the password from standard input instead of the terminal device. -- The -- flag indicates that sudo should stop processing command line arguments. It is most useful in conjunction with the -s flag. RETURN VALUES
Upon successful execution of a program, the return value from sudo will simply be the return value of the program that was executed. Otherwise, sudo quits with an exit value of 1 if there is a configuration/permission problem or if sudo cannot execute the given command. In the latter case the error string is printed to stderr. If sudo 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. SECURITY NOTES
sudo tries to be safe when executing external commands. Variables that control how dynamic loading and binding is done can be used to sub- vert the program that sudo 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. sudo will also remove the IFS, ENV, BASH_ENV, KRB_CONF, KRBCONFDIR, KRBTKFILE, KRB5_CONFIG, LOCALDOMAIN, RES_OPTIONS, HOSTALIASES, NLSPATH, PATH_LOCALE, TERMINFO, TERMINFO_DIRS and TERMPATH variables as they too can pose a threat. If the TERMCAP variable is set and is a pathname, it too is ignored. Additionally, if the LC_* or LANGUAGE vari- ables contain the / or % characters, they are ignored. If sudo has been compiled with SecurID support, the VAR_ACE, USR_ACE and DLC_ACE variables are cleared as well. The list of environment variables that sudo clears is contained in the output of sudo -V when run as root. To prevent command spoofing, 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 PATH environment variable is not modified and is passed unchanged to the program that 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 sudo statically. sudo 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 sudo is run. However, because 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 (/var/adm/sudo for instance) or create /var/run/sudo with the appropriate owner (root) and permissions (0700) in the system startup files. sudo 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 systems that allow users to give away files. Please note that sudo will only log the command it explicitly runs. If a user runs a command such as sudo su or sudo sh, subsequent com- mands run from that shell will not be logged, nor will 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 sudo to verify that the command does not inadvertantly give the user an effective root shell. 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 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 cd and file redirection work. % sudo sh -c "cd /home ; du -s * | sort -rn > USAGE" ENVIRONMENT
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 FILES
/etc/sudoers List of who can run what /var/run/sudo Directory containing timestamps AUTHORS
Many people have worked on sudo over the years; this version consists of code written primarily by: Todd Miller Chris Jepeway See the HISTORY file in the sudo distribution or visit http://www.sudo.ws/sudo/history.html for a short history of sudo. BUGS
If you feel you have found a bug in sudo, please submit a bug report at http://www.sudo.ws/sudo/bugs/ DISCLAIMER
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 sudo for complete details. 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 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 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). SEE ALSO
stat(2), login_cap(3), sudoers(5), passwd(5), visudo(8), grep(1), su(1). 3rd Berkeley Distribution 1.6.6 sudo(8)
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