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SUDO(8)                      MAINTENANCE COMMANDS                      SUDO(8)

NAME
       sudo, sudoedit - execute a command as another user

SYNOPSIS
       sudo -h | -K | -k | -L | -l | -V | -v

       sudo [-bEHPS] [-p prompt] [-u username|#uid] [VAR=value]
       {-i | -s | command}

       sudoedit [-S] [-p prompt] [-u username|#uid] file ...

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 effective
       uid and gid are set to match those of the target user as specified in
       the passwd file and the group vector is initialized based on the group
       file (unless the -P option was specified).  If the invoking user is
       root or if the target user is the same as the invoking user, no pass-
       word is required.  Otherwise, sudo requires that users authenticate
       themselves with a password by default (NOTE: in the default configura-
       tion 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 (15 minutes
       unless overridden in sudoers).

       When invoked as sudoedit, the -e option (described below), is implied.

       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 0 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 config-
       ure time or in 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.

       If sudo is run by root and the SUDO_USER environment variable is set,
       sudo will use this value to determine who the actual user is.  This can
       be used by a user to log commands through sudo even when a root shell
       has been invoked.  It also allows the -e flag to remain useful even
       when being run via a sudo-run script or program.  Note however, that
       the sudoers lookup is still done for root, not the user specified by
       SUDO_USER.

       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 sudo-
       ers file.

OPTIONS
       sudo accepts the following command line options:

       -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.

       -E  The -E (preserve environment) option will override the env_reset
           option in sudoers(5)).  It is only available when either the
           matching command has the SETENV tag or the setenv option is set in
           sudoers(5).

       -e  The -e (edit) option indicates that, instead of running a command,
           the user wishes to edit one or more files.  In lieu of a command,
           the string "sudoedit" is used when consulting the sudoers file.  If
           the user is authorized by sudoers the following steps are taken:

           1.  Temporary copies are made of the files to be edited with the
               owner set to the invoking user.

           2.  The editor specified by the VISUAL or EDITOR environment vari-
               ables is run to edit the temporary files.  If neither VISUAL
               nor EDITOR are set, the program listed in the editor sudoers
               variable is used.

           3.  If they have been modified, the temporary files are copied back
               to their original location and the temporary versions are
               removed.

           If the specified file does not exist, it will be created.  Note
           that unlike most commands run by sudo, the editor is run with the
           invoking user's environment unmodified.  If, for some reason, sudo
           is unable to update a file with its edited version, the user will
           receive a warning and the edited copy will remain in a temporary
           file.

       -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 (see set_home and
           always_set_home in sudoers(5)).

       -h  The -h (help) option causes sudo to print a usage message and exit.

       -i  The -i (simulate initial login) option runs the shell specified in
           the passwd(5) entry of the user that the command is being run as.
           The command name argument given to the shell begins with a `-' to
           tell the shell to run as a login shell.  sudo attempts to change to
           that user's home directory before running the shell.  It also ini-
           tializes the environment, leaving TERM unchanged, setting HOME,
           SHELL, USER, LOGNAME, and PATH, and unsetting all other environment
           variables.  Note that because the shell to use is determined before
           the sudoers file is parsed, a runas_default setting in sudoers will
           specify the user to run the shell as but will not affect which
           shell is actually run.

       -K  The -K (sure kill) option is like -k except that it removes the
           user's timestamp entirely.  Like -k, this option does not require a
           password.

       -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.

       -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).

       -l  The -l (list) option will list out the allowed (and forbidden) com-
           mands for the invoking user on the current host.

       -P  The -P (preserve group vector) option causes sudo to preserve the
           invoking user's group vector unaltered.  By default, sudo will ini-
           tialize 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.

       -p  The -p (prompt) option allows you to override the default password
           prompt and use a custom one.  The following percent (`%') escapes
           are supported:

           %H  expanded to the local hostname including the domain name (on if
               the machine's hostname is fully qualified or the fqdn sudoers
               option is set)

           %h  expanded to the local hostname without the domain name

           %p  expanded to the user whose password is being asked for
               (respects the rootpw, targetpw and runaspw flags in sudoers)

           %U  expanded to the login name of the user the command will be run
               as (defaults to root)

           %u  expanded to the invoking user's login name

           %%  two consecutive % characters are collapsed into a single %
               character

       -S  The -S (stdin) option causes sudo to read the password from the
           standard input instead of the terminal device.

       -s  The -s (shell) option runs the shell specified by the SHELL envi-
           ronment variable if it is set or the shell as specified in
           passwd(5).

       -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.  When running commands as a uid, many shells require that the
           '#' be escaped with a backslash ('\').  Note that if the targetpw
           Defaults option is set (see sudoers(5)) it is not possible to run
           commands with a uid not listed in the password database.

       -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.

       -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 15 minutes (or whatever the
           timeout is set to in sudoers) but does not run a command.

       --  The -- flag indicates that sudo should stop processing command line
           arguments.  It is most useful in conjunction with the -s flag.

       Environment variables to be set for the command may also be passed on
       the command line in the form of VAR=value, e.g.
       LD_LIBRARY_PATH=/usr/local/pkg/lib.  Variables passed on the command
       line are subject to the same restrictions as normal environment vari-
       ables with one important exception.  If the setenv option is set in
       sudoers, the command to be run has the SETENV tag set or the command
       matched is ALL, the user may set variables that would overwise be for-
       bidden.  See sudoers(5) for more information.

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 configura-
       tion/permission problem or if sudo cannot execute the given command.
       In the latter case the error string is printed to stderr.  If sudo can-
       not 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 auto-
       mounter 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.

       There are two distinct ways to deal with environment variables.  By
       default, the env_reset sudoers option is enabled.  This causes commands
       to be executed with a minimal environment containing TERM, PATH, HOME,
       SHELL, LOGNAME, USER and USERNAME in addition to variables from the
       invoking process permitted by the env_check and env_keep sudoers
       options.  There is effectively a whitelist for environment variables.

       If, however, the env_reset option is disabled in sudoers, any variables
       not explicitly denied by the env_check and env_delete options are
       inherited from the invoking process.  In this case, env_check and
       env_delete behave like a blacklist.  Since it is not possible to black-
       list all potentially dangerous environment variables, use of the
       default env_reset behavior is encouraged.

       In all cases, environment variables with a value beginning with () are
       removed as they could be interpreted as bash functions.  The list of
       environment variables that sudo allows or denies is contained in the
       output of sudo -V when run as root.

       Note that the dynamic linker on most operating systems will remove
       variables that can control dynamic linking from the environment of
       setuid executables, including sudo.  Depending on the operating system
       this may include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and
       others.  These type of variables are removed from the environment
       before sudo even begins execution and, as such, it is not possible for
       sudo to preserve them.

       To prevent command spoofing, sudo checks "." and "" (both denoting cur-
       rent directory) last when searching for a command in the user's PATH
       (if one or both are in the PATH).  Note, however, that the PATH envi-
       ronment variable is further modified in Debian because of the use of
       the SECURE_PATH build option.

       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 or if it is writable by a user other than 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 direc-
       tory 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 cre-
       ate /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 normally only log the command it explicitly
       runs.  If a user runs a command such as sudo su or sudo sh, subsequent
       commands 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 com-
       mand does not inadvertently give the user an effective root shell.  For
       more information, please see the PREVENTING SHELL ESCAPES section in
       sudoers(5).

ENVIRONMENT
       sudo utilizes the following environment variables:

       EDITOR          Default editor to use in -e (sudoedit) mode if VISUAL
                       is not set

       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

       PATH            Set to a sane value if the secure_path sudoers option
                       is set.

       SHELL           Used to determine shell to run with -s option

       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

       USER            Set to the target user (root unless the -u option is
                       specified)

       VISUAL          Default editor to use in -e (sudoedit) mode

FILES
       /etc/sudoers            List of who can run what

       /var/run/sudo           Directory containing timestamps

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 file
       system 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"

SEE ALSO
       grep(1), su(1), stat(2), passwd(5), sudoers(5), visudo(8)

       The file /usr/share/doc/sudo/OPTIONS describes the options used for
       building the Debian version of sudo, some of which change default
       behaviors documented elsewhere in this document.

AUTHORS
       Many people have worked on sudo over the years; this version consists
       of code written primarily by:

               Todd C. 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.

CAVEATS
       There is no easy way to prevent a user from gaining a root shell if
       that user is allowed to run arbitrary commands via sudo.  Also, many
       programs (such as editors) allow the user to run commands via shell
       escapes, thus avoiding sudo's checks.  However, on most systems it is
       possible to prevent shell escapes with sudo's noexec functionality.
       See the sudoers(5) manual for details.

       It is not meaningful to run the cd command directly via sudo, e.g.,

        $ sudo cd /usr/local/protected

       since when the command exits the parent process (your shell) will still
       be the same.  Please see the EXAMPLES section for more information.

       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
       has a /dev/fd/ directory, setuid shell scripts are generally safe).

BUGS
       If you feel you have found a bug in sudo, please submit a bug report at
       http://www.sudo.ws/sudo/bugs/

SUPPORT
       Limited free support is available via the sudo-users mailing list, see
       http://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search
       the archives.

DISCLAIMER
       sudo is provided ``AS IS'' and any express or implied warranties,
       including, but not limited to, the implied warranties of merchantabil-
       ity and fitness for a particular purpose are disclaimed.  See the
       LICENSE file distributed with sudo or
       http://www.sudo.ws/sudo/license.html for complete details.

1.6.9p17                         Jun 21, 2008                          SUDO(8)

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