Difference between revisions of "Sudo"

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=== Defaults Skeleton ===
 
=== Defaults Skeleton ===
  
At [http://www.gratisoft.us/sudo/sudoers.man.html#sudoers_options this link] you can find a list of all the options available to use with the {{ic|Defaults}} command in {{ic|/etc/sudoers}}.
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The authors site has a [http://www.gratisoft.us/sudo/sudoers.man.html#sudoers_options list of all the options] that can be used with the {{ic|Defaults}} command in the {{ic|/etc/sudoers}} file.
  
{{Poor writing|the comments in the following block of code are truncated.}}
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The full list of options ''(parsed from the version 1.8.7 source code)'' is below in a format optimized for copying and pasting into your sudoers files for quick editing.
The same list is reproduced right below in a format optimized for copying and pasting it in your sudoers files and then make changes.
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{{bc|<nowiki>
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{{bc|<nowiki>#Defaults always_set_home
#Defaults       always_set_home
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# If enabled, sudo will set the HOME environment variable to the home directory of the target user
# always_set_home: If enabled, sudo will set the HOME environment variable to the home directory of the target user (which is root unless the -u option is used).  This effectively means that the -H op
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(which is root unless the -u option is used).  This effectively means that the -H option
#     always_set_home is only effective for configurations where either env_reset is disabled or HOME is present in the env_keep list.  This flag is off by default.
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# always_set_home is only effective for configurations where either env_reset is disabled or HOME is present
 +
in the env_keep list.  Default: OFF
  
#Defaults       authenticate
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#Defaults authenticate
# authenticate: If set, users must authenticate themselves via a password (or other means of authentication) before they may run commands.  This default may be overridden via the PASSWD and NOPASSWD t
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# If set, users must authenticate themselves via a password (or other means of authentication)
 +
before they may run commands.  This default may be overridden via the PASSWD and NOPASSWD
  
#Defaults       closefrom_override
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#Defaults closefrom_override
# closefrom_override: If set, the user may use sudo's -C option which overrides the default starting point at which sudo begins closing open file descriptors.  This flag is off by default.
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# If set, the user may use sudo's -C option which overrides the default starting
 +
point at which sudo begins closing open file descriptors.  Default: OFF
  
#Defaults       compress_io
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#Defaults compress_io
# compress_io: If set, and sudo is configured to log a command's input or output, the I/O logs will be compressed using zlib.  This flag is on by default when sudo is compiled with zlib support.
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# If set, and sudo is configured to log a command's input or output, the I/O logs will be
 +
compressed using zlib.  This flag is on by default when sudo is compiled with zlib support.
  
#Defaults       env_editor
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#Defaults env_editor
# env_editor: If set, visudo will use the value of the EDITOR or VISUAL environment variables before falling back on the default editor list.  Note that this may create a security hole as it allows th
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# If set, visudo will use the value of the EDITOR or VISUAL environment variables before falling back on the default
separated list of editors in the editor variable.  visudo will then only use the EDITOR or VISUAL if they match a value specified in editor.  This flag is on by default.
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editor list.  Note that this may create a security hole as it allows th separated list of editors in the editor
 +
variable.  visudo will then only use the EDITOR or VISUAL if they match a value specified in editor.  On by default.
  
#Defaults       env_reset
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#Defaults env_reset
# env_reset: If set, sudo will run the command in a minimal environment containing the TERM, PATH, HOME, MAIL, SHELL, LOGNAME, USER, USERNAME and SUDO_* variables.  Any variables in the caller's envir
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# If set, sudo will run the command in a minimal environment containing the TERM, PATH, HOME, MAIL, SHELL, LOGNAME,
in the file specified by the env_file option (if any).  The default contents of the env_keep and env_check lists are displayed when sudo is run by root with the -V option.  If the secure_path opti
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USER, USERNAME and SUDO_* variables.  Any variables in the caller's env in the file specified by the env_file
#  default.
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option (if any).  The default contents of the env_keep and env_check lists are displayed when sudo is run by
 +
root with the -V option.
  
#Defaults       fast_glob
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#Defaults fast_glob
# fast_glob: Normally, sudo uses the glob(3) function to do shell-style globbing when matching path names.  However, since it accesses the file system, glob(3) can take a long time to complete for som
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# Normally, sudo uses the glob(3) function to do shell-style globbing when matching path names.
(automounted).  The fast_glob option causes sudo to use the fnmatch(3) function, which does not access the file system to do its matching.  The disadvantage of fast_glob is that it is unable to ma
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# However, since it accesses the file system, glob(3) can take a long time to complete for som (automounted).
names that include globbing characters are used with the negation operator, '!', as such rules can be trivially bypassed.  As such, this option should not be used when sudoers contains rules that
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# The fast_glob option causes sudo to use the fnmatch(3) function, which does not access the file system to do
 +
its matching.  The disadvantage of fast_glob is that it is unable to ma names that include globbing characters
 +
are used with the negation operator, '!', as such rules can be trivially bypassed.  As such, this option should
 +
not be used when sudoers contains rules that
  
#Defaults       fqdn
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#Defaults fqdn
# fqdn: Set this flag if you want to put fully qualified host names in the sudoers file.  I.e., instead of myhost you would use myhost.mydomain.edu.  You may still use the short form if you wish (and
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# Set this flag if you want to put fully qualified host names in the sudoers file.  I.e., instead of myhost you
sudo unusable if DNS stops working (for example if the machine is not plugged into the network).  Also note that you must use the host's official name as DNS knows it.  That is, you may not use a
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would use myhost.mydomain.edu.  You may still use the short form if you wish (and sudo unusable if DNS stops
#    all aliases from DNS.  If your machine's host name (as returned by the hostname command) is already fully qualified you shouldn't need to set fqdn.  This flag is off by default.
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working (for example if the machine is not plugged into the network).  Also note that you must use the
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host's official name as DNS knows it.  That is, you may not use a all aliases from DNS.  If your machine's
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host name (as returned by the hostname command) is already fully qualified you shouldn't need to set fqdn.
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# Default: OFF
  
#Defaults       ignore_dot
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#Defaults ignore_dot
# ignore_dot: If set, sudo will ignore '.' or '' (current dir) in the PATH environment variable; the PATH itself is not modified.  This flag is off by default.
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# If set, sudo will ignore '.' or '' (current dir) in the PATH environment variable; the PATH
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itself is not modified.  Default: OFF
  
#Defaults       ignore_local_sudoers
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#Defaults ignore_local_sudoers
# ignore_local_sudoers: If set via LDAP, parsing of /etc/sudoers will be skipped.  This is intended for Enterprises that wish to prevent the usage of local sudoers files so that only LDAP is used.  Th
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# If set via LDAP, parsing of /etc/sudoers will be skipped.  This is intended for Enterprises that wish to prevent
#  present, /etc/sudoers does not even need to exist. Since this option tells sudo how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for the cn=default
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the usage of local sudoers files so that only LDAP is used.  /etc/sudoers does not even need to exist.
 +
Since this option tells sudo how to behave when no specific LDAP entries have been matched, this sudo
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#  Option is only meaningful for the cn=default
  
#Defaults       insults
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#Defaults insults
# insults: If set, sudo will insult users when they enter an incorrect password.  This flag is off by default.
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# If set, sudo will insult users when they enter an incorrect password.  Default: OFF
  
#Defaults       log_host
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#Defaults log_host
# log_host: If set, the host name will be logged in the (non-syslog) sudo log file.  This flag is off by default.
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# If set, the host name will be logged in the (non-syslog) sudo log file.  Default: OFF
  
#Defaults       log_input
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#Defaults log_input
# log_input: If set, sudo will run the command in a pseudo tty and log all user input.  If the standard input is not connected to the user's tty, due to I/O redirection or because the command is part
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# If set, sudo will run the command in a pseudo tty and log all user input.  If the standard
Input is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=.  The i
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input is not connected to the user's tty, due to I/O redirection or because the command is part Input is logged
Note that user input may contain sensitive information such as passwords (even if they are not echoed to the screen), which will be stored in the log file unencrypted. In most cases, logging the
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to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that
 +
is included in the normal sudo log line, prefixed with TSID=.  Note that user input may contain sensitive
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information such as passwords (even if they are not echoed to the screen), which will be stored in the log file
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unencrypted.
  
#Defaults       log_output
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#Defaults log_output
# log_output: If set, sudo will run the command in a pseudo tty and log all output that is sent to the screen, similar to the script(1) command.  If the standard output or standard error is not connec
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# If set, sudo will run the command in a pseudo tty and log all output that is sent to the
is also captured and stored in separate log files.
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screen, similar to the script(1) command.  If the standard output or standard error is not connec is also captured and
Output is logged to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=.  The
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stored in separate log files. Output is logged to the directory specified by the iolog_dir option (/var/log/sudo-io
#   Output logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.
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by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=.  The Output
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# logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.
  
#Defaults       log_year
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#Defaults log_year
# log_year: If set, the four-digit year will be logged in the (non-syslog) sudo log file.  This flag is off by default.
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# If set, the four-digit year will be logged in the (non-syslog) sudo log file.  Default: OFF
  
#Defaults       long_otp_prompt
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#Defaults long_otp_prompt
# long_otp_prompt: When validating with a One Time Password (OTP) scheme such as S/Key or OPIE, a two-line prompt is used to make it easier to cut and paste the challenge to a local window.  It's not
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# When validating with a One Time Password (OTP) scheme such as S/Key or OPIE, a two-line
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prompt is used to make it easier to cut and paste the challenge to a local window
  
#Defaults       mail_always
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#Defaults mail_always
# mail_always: Send mail to the mailto user every time a users runs sudo.  This flag is off by default.
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# Send mail to the mailto user every time a users runs sudo.  Default: OFF
  
#Defaults       mail_badpass
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#Defaults mail_badpass
# mail_badpass: Send mail to the mailto user if the user running sudo does not enter the correct password.  This flag is off by default.
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# Send mail to the mailto user if the user running sudo does not enter the correct password.
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# Default: OFF
  
#Defaults       mail_no_host
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#Defaults mail_no_host
# mail_no_host: If set, mail will be sent to the mailto user if the invoking user exists in the sudoers file, but is not allowed to run commands on the current host.  This flag is off by default.
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# If set, mail will be sent to the mailto user if the invoking user exists in the sudoers
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file, but is not allowed to run commands on the current host.  Default: OFF
  
#Defaults       mail_no_perms
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#Defaults mail_no_perms
# mail_no_perms: If set, mail will be sent to the mailto user if the invoking user is allowed to use sudo but the command they are trying is not listed in their sudoers file entry or is explicitly den
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# If set, mail will be sent to the mailto user if the invoking user is allowed to use sudo
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but the command they are trying is not listed in their sudoers file entry or is explicitly denied
  
#Defaults       mail_no_user
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#Defaults mail_no_user
# mail_no_user: If set, mail will be sent to the mailto user if the invoking user is not in the sudoers file.  This flag is on by default.
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# If set, mail will be sent to the mailto user if the invoking user is not in the sudoers file.
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# Default: ON
  
#Defaults       noexec
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#Defaults noexec
# noexec: If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless overridden by a EXEC tag.  See the description of NOEXEC and EXEC below as well as the "PREVENTING SHE
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# If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless overridden
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by a EXEC tag.  See the description of NOEXEC and EXEC below as well as the "PREVENTING SHE
  
#Defaults       path_info
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#Defaults path_info
# path_info: Normally, sudo will tell the user when a command could not be found in their PATH environment variable.  Some sites may wish to disable this as it could be used to gather information on t
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# Normally, sudo will tell the user when a command could not be found in their PATH environment
the executable is simply not in the user's PATH, sudo will tell the user that they are not allowed to run it, which can be confusing.  This flag is on by default.
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variable.  Some sites may wish to disable this as it could be used to gather information on t the executable is
 +
simply not in the user's PATH, sudo will tell the user that they are not allowed to run it, which can be confusing.
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# Default: ON
  
#Defaults       passprompt_override
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#Defaults passprompt_override
# passprompt_override: The password prompt specified by passprompt will normally only be used if the password prompt provided by systems such as PAM matches the string "Password:".  If passprompt_over
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# The password prompt specified by passprompt will normally only be used if the password prompt provided by
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systems such as PAM matches the string "Password:"
  
#Defaults       preserve_groups
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#Defaults preserve_groups
# preserve_groups: By default, sudo will initialize the group vector to the list of groups the target user is in.  When preserve_groups is set, the user's existing group vector is left unaltered.  The
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# By default, sudo will initialize the group vector to the list of groups the target
#  default.
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user is in.  When preserve_groups is set, the user's existing group vector is left unaltered.
  
#Defaults       pwfeedback
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#Defaults pwfeedback
# pwfeedback: By default, sudo reads the password like most other Unix programs, by turning off echo until the user hits the return (or enter) key.  Some users become confused by this as it appears to
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# By default, sudo reads the password like most other Unix programs, by turning off echo
the user presses a key.  Note that this does have a security impact as an onlooker may be able to determine the length of the password being entered.  This flag is off by default.
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until the user hits the return (or enter) key.  Some users become confused by this as it appears to the user
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presses a key.  Note that this does have a security impact as an onlooker may be able to determine the length of
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the password being entered.  Default: OFF
  
#Defaults       requiretty
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#Defaults requiretty
# requiretty: If set, sudo will only run when the user is logged in to a real tty.  When this flag is set, sudo can only be run from a login session and not via other means such as cron(8) or cgi-bin
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# If set, sudo will only run when the user is logged in to a real tty.  When this flag is set,
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sudo can only be run from a login session and not via other means such as cron(8) or cgi-bin
  
#Defaults       root_sudo
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#Defaults root_sudo
# root_sudo: If set, root is allowed to run sudo too.  Disabling this prevents users from "chaining" sudo commands to get a root shell by doing something like "sudo sudo /bin/sh".  Note, however, that
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# If set, root is allowed to run sudo too.  Disabling this prevents users from "chaining" sudo
real additional security; it exists purely for historical reasons.  This flag is on by default.
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commands to get a root shell by doing something like "sudo sudo /bin/sh".  Note, however, that real additional
 +
security; it exists purely for historical reasons.  Default: ON
  
#Defaults       rootpw
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#Defaults rootpw
# rootpw: If set, sudo will prompt for the root password instead of the password of the invoking user.  This flag is off by default.
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# If set, sudo will prompt for the root password instead of the password of the invoking user.
 +
# Default: OFF
  
#Defaults       runaspw
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#Defaults runaspw
# runaspw: If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to root) instead of the password of the invoking user.  This flag is off by default.
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# If set, sudo will prompt for the password of the user defined by the runas_default option
 +
(defaults to root) instead of the password of the invoking user.  Default: OFF
  
#Defaults       set_home
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#Defaults set_home
# set_home: If enabled and sudo is invoked with the -s option the HOME environment variable will be set to the home directory of the target user (which is root unless the -u option is used).  This eff
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# If enabled and sudo is invoked with the -s option the HOME environment variable will be set
#  is enabled, so set_home is only effective for configurations where either env_reset is disabled or HOME is present in the env_keep list.  This flag is off by default.
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to the home directory of the target user (which is root unless the -u option is used).  So set_home is only
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effective for configs where either env_reset is disabled or HOME is present in the env_keep list.  Default: OFF
  
#Defaults       set_logname
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#Defaults set_logname
# set_logname: Normally, sudo will set the LOGNAME, USER and USERNAME environment variables to the name of the target user (usually root unless the -u option is given).  However, since some programs (
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# Normally, sudo will set the LOGNAME, USER and USERNAME environment variables to the name
may be desirable to change this behavior.  This can be done by negating the set_logname option.  Note that if the env_reset option has not been disabled, entries in the env_keep list will override
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of the target user (usually root unless the -u option is given).  However, since some programs ( may be desirable
 +
to change this behavior.  This can be done by negating the set_logname option.  Note that if the env_reset option
 +
has not been disabled, entries in the env_keep list will override
  
#Defaults       set_utmp
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#Defaults set_utmp
# set_utmp: When enabled, sudo will create an entry in the utmp (or utmpx) file when a pseudo-tty is allocated.  A pseudo-tty is allocated by sudo when the log_input, log_output or use_pty flags are e
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# When enabled, sudo will create an entry in the utmp (or utmpx) file when a pseudo-tty is
the tty, time, type and pid fields updated.  This flag is on by default.
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allocated.  A pseudo-tty is allocated by sudo when the log_input, log_output or use_pty flags are e the tty, time,
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type and pid fields updated.  Default: ON
  
#Defaults       setenv
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#Defaults setenv
# setenv: Allow the user to disable the env_reset option from the command line via the -E option.  Additionally, environment variables set via the command line are not subject to the restrictions impo
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# Allow the user to disable the env_reset option from the command line via the -E option.
#   variables in this manner.  This flag is off by default.
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# Additionally, environment variables set via the command line are not subject to the restrictions impo variables
 +
# in this manner.  Default: OFF
  
#Defaults       shell_noargs
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#Defaults shell_noargs
# shell_noargs: If set and sudo is invoked with no arguments it acts as if the -s option had been given.  That is, it runs a shell as root (the shell is determined by the SHELL environment variable if
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# If set and sudo is invoked with no arguments it acts as if the -s option had been given.
is off by default.
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# That is, it runs a shell as root (the shell is determined by the SHELL environment variable if is off by default.
  
#Defaults       stay_setuid
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#Defaults stay_setuid
# stay_setuid: Normally, when sudo executes a command the real and effective UIDs are set to the target user (root by default).  This option changes that behavior such that the real UID is left as the
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# Normally, when sudo executes a command the real and effective UIDs are set to the target
systems that disable some potentially dangerous functionality when a program is run setuid.  This option is only effective on systems with either the setreuid() or setresuid() function.  This flag
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user (root by default).  This option changes that behaviour such that the real UID is left as the systems that
 +
disable some potentially dangerous functionality when a program is run setuid.  This option is only effective on
 +
systems with either the setreuid() or setresuid() function.  This flag
  
#Defaults       targetpw
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#Defaults targetpw
# targetpw: If set, sudo will prompt for the password of the user specified by the -u option (defaults to root) instead of the password of the invoking user.  In addition, the timestamp file name will
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# If set, sudo will prompt for the password of the user specified by the -u option (defaults to root) instead
passwd database as an argument to the -u option.  This flag is off by default.
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of the password of the invoking user.  In addition, the timestamp file name will passwd database as an argument
 +
to the -u option.  Default: OFF
  
#Defaults       tty_tickets
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#Defaults tty_tickets
# tty_tickets: If set, users must authenticate on a per-tty basis.  With this flag enabled, sudo will use a file named for the tty the user is logged in on in the user's time stamp directory. If disa
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# If set, users must authenticate on a per-tty basis.  With this flag enabled, sudo will
 +
use a file named for the tty the user is logged in on in the user's time stamp directory.
  
#Defaults       umask_override
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#Defaults umask_override
# umask_override: If set, sudo will set the umask as specified by sudoers without modification.  This makes it possible to specify a more permissive umask in sudoers than the user's own umask and matc
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# If set, sudo will set the umask as specified by sudoers without modification.  This makes
user's umask and what is specified in sudoers.  This flag is off by default.
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it possible to specify a more permissive umask in sudoers than the user's own umask and match user's umask and what
 +
is specified in sudoers.  Default: OFF
  
#Defaults       use_pty
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#Defaults use_pty
# use_pty: If set, sudo will run the command in a pseudo-pty even if no I/O logging is being gone.  A malicious program run under sudo could conceivably fork a background process that retains to the u
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# If set, sudo will run the command in a pseudo-pty even if no I/O logging is being gone.
that impossible.  This flag is off by default.
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# A malicious program run under sudo could conceivably fork a background process that retains to the u that impossible.
 +
# Default: OFF
  
#Defaults       utmp_runas
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#Defaults utmp_runas
# utmp_runas: If set, sudo will store the name of the runas user when updating the utmp (or utmpx) file.  By default, sudo stores the name of the invoking user.  This flag is off by default.
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# If set, sudo will store the name of the runas user when updating the utmp (or utmpx) file.
 +
# By default, sudo stores the name of the invoking user.  Default: OFF
  
#Defaults       visiblepw
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#Defaults visiblepw
# visiblepw: By default, sudo will refuse to run if the user must enter a password but it is not possible to disable echo on the terminal. If the visiblepw flag is set, sudo will prompt for a passwor
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# By default, sudo will refuse to run if the user must enter a password but it is not possible to disable echo on the  
#   somehost sudo ls" since rsh(1) does not allocate a tty. This flag is off by default.
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terminal. If the visiblepw flag is set, sudo will prompt for a password even when it would be visible on the screen.
 +
# This makes it possible to run things like "rsh somehost sudo ls" since rsh(1) does not allocate a tty. Default: OFF
  
#Defaults       closefrom
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#Defaults closefrom
# closefrom: Before it executes a command, sudo will close all open file descriptors other than standard input, standard output and standard error (ie: file descriptors 0-2). The closefrom option can
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# Before it executes a command, sudo will close all open file descriptors other than standard
 +
input, standard output and standard error (ie: file descriptors 0-2).
  
#Defaults       passwd_tries
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#Defaults passwd_tries
# passwd_tries: The number of tries a user gets to enter his/her password before sudo logs the failure and exits.  The default is 3.
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# The number of tries a user gets to enter his/her password before sudo logs the failure
 +
and exits.  The default is 3.
  
#Defaults       loglinelen
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#Defaults loglinelen
# loglinelen: Number of characters per line for the file log.  This value is used to decide when to wrap lines for nicer log files.  This has no effect on the syslog log file, only the file log. The
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# Number of characters per line for the file log.  This value is used to decide when to wrap
 +
lines for nicer log files.  This has no effect on the syslog log file, only the file log.
  
#Defaults       passwd_timeout
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#Defaults passwd_timeout
# passwd_timeout: Number of minutes before the sudo password prompt times out, or 0 for no timeout.  The timeout may include a fractional component if minute granularity is insufficient, for example 2
+
# Number of minutes before the sudo password prompt times out, or 0 for no timeout.
 +
# The timeout may include a fractional component if minute granularity is insufficient, for example 2
  
#Defaults       timestamp_timeout
+
#Defaults timestamp_timeout
# timestamp_timeout: Number of minutes that can elapse before sudo will ask for a passwd again.  The timeout may include a fractional component if minute granularity is insufficient, for example 2.5.
+
# Number of minutes that can elapse before sudo will ask for a passwd again.  The timeout
timestamp will never expire.  This can be used to allow users to create or delete their own timestamps via sudo -v and sudo -k respectively.
+
may include a fractional component if minute granularity is insufficient, for example 2.5. timestamp will never expire.
 +
# This can be used to allow users to create or delete their own timestamps via sudo -v and sudo -k respectively.
  
#Defaults       umask
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#Defaults umask
# umask: Umask to use when running the command.  Negate this option or set it to 0777 to preserve the user's umask.  The actual umask that is used will be the union of the user's umask and the value o
+
# Umask to use when running the command.  Negate this option or set it to 0777 to preserve
#   running a command.  Note on systems that use PAM, the default PAM configuration may specify its own umask which will override the value set in sudoers.
+
the user's umask.  The actual umask that is used will be the union of the user's umask and the value o running
 +
# a command.  Note on systems that use PAM, the default PAM configuration may specify its own umask which will
 +
override the value set in sudoers.
  
#Defaults       badpass_message
+
#Defaults badpass_message
# badpass_message: Message that is displayed if a user enters an incorrect password.  The default is Sorry, try again. unless insults are enabled.
+
# Message that is displayed if a user enters an incorrect password.  The default is Sorry,
 +
try again. unless insults are enabled.
  
#Defaults       editor
+
#Defaults editor
# editor: A colon (':') separated list of editors allowed to be used with visudo.  visudo will choose the editor that matches the user's EDITOR environment variable if possible, or the first editor in
+
# A colon (':') separated list of editors allowed to be used with visudo.  visudo will choose
 +
the editor that matches the user's EDITOR environment variable if possible, or the first editor in
  
#Defaults       iolog_dir
+
#Defaults iolog_dir
# iolog_dir: The top-level directory to use when constructing the path name for the input/output log directory.  Only used if the log_input or log_output options are enabled or when the LOG_INPUT or L
+
# The top-level directory to use when constructing the path name for the input/output log
#   directory. The default is "/var/log/sudo-io".
+
directory.  Only used if the log_input or log_output options are enabled or when the LOG_INPUT or L directory.
The following percent (`%') escape sequences are supported:
+
#  The default is "/var/log/sudo-io". The following percent (%) escape sequences are supported:
#     %{seq} - expanded to a monotonically increasing base-36 sequence number, such as 0100A5, where every two digits are used to form a new directory, e.g. 01/00/A5
+
#   %{seq}         - expanded to base-36 sequence number, such as 0100A5, to form a new directory, e.g. 01/00/A5
#     %{user} - expanded to the invoking user's login name
+
#   %{user}       - expanded to the invoking user's login name
#     %{group} - expanded to the name of the invoking user's real group ID
+
#   %{group}       - expanded to the name of the invoking user's real group ID
#     %{runas_user} - expanded to the login name of the user the command will be run as (e.g. root)
+
#   %{runas_user} - expanded to the login name of the user the command will be run as (e.g. root)
#     %{runas_group} - expanded to the group name of the user the command will be run as (e.g. wheel)
+
#   %{runas_group} - expanded to the group name of the user the command will be run as (e.g. wheel)
#     %{hostname} - expanded to the local host name without the domain name
+
#   %{hostname}   - expanded to the local host name without the domain name
#     %{command} - expanded to the base name of the command being run
+
#   %{command}     - expanded to the base name of the command being run In addition, any escape sequences supported by
In addition, any escape sequences supported by the system's strftime() function will be expanded.
+
#                    strftime() function will be expanded. To include a literal % character, the string %% should be used.
To include a literal `%' character, the string `%%' should be used.
+
  
#Defaults       iolog_file
+
#Defaults iolog_file
# iolog_file: The path name, relative to iolog_dir, in which to store input/output logs when the log_input or log_output options are enabled or when the LOG_INPUT or LOG_OUTPUT tags are present for a
+
# The path name, relative to iolog_dir, in which to store input/output logs when the log_input or log_output options are
See the iolog_dir option above for a list of supported percent (`%') escape sequences.
+
enabled or when the LOG_INPUT or LOG_OUTPUT tags are present for a See the iolog_dir option above for a list of
In addition to the escape sequences, path names that end in six or more Xs will have the Xs replaced with a unique combination of digits and letters, similar to the mktemp() function.
+
supported percent (%) escape sequences. In addition to the escape sequences, path names that end in six or more Xs will
 +
have the Xs replaced with a unique combination of digits and letters, similar to the mktemp() function.
  
#Defaults       mailsub
+
#Defaults mailsub
# mailsub: Subject of the mail sent to the mailto user. The escape %h will expand to the host name of the machine.  Default is *** SECURITY information for %h ***.
+
# Subject of the mail sent to the mailto user. The escape %h will expand to the host name of
 +
the machine.  Default is *** SECURITY information for %h ***.
  
#Defaults       noexec_file
+
#Defaults noexec_file
# noexec_file: This option is no longer supported.  The path to the noexec file should now be set in the /etc/sudo.conf file.
+
# This option is no longer supported.  The path to the noexec file should now be set in the /etc/sudo.conf file.
  
#Defaults       passprompt
+
#Defaults passprompt
# passprompt: The default prompt to use when asking for a password; can be overridden via the -p option or the SUDO_PROMPT environment variable.  The following percent (`%') escape sequences are suppo
+
# The default prompt to use when asking for a password; can be overridden via the -p option or the SUDO_PROMPT
#     %H expanded to the local host name including the domain name (only if the machine's host name is fully qualified or the fqdn option is set)
+
environment variable.  The following percent (%) escape sequences are supported:
#     %h expanded to the local host name without the domain name
+
#   %H - expanded to the local host name including the domain (only if the host name is fqdn or fqdn option is set)
#     %p expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)
+
#   %h - expanded to the local host name without the domain name
#     %U expanded to the login name of the user the command will be run as (defaults to root)
+
#   %p - expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags)
#     %u expanded to the invoking user's login name
+
#   %U - expanded to the login name of the user the command will be run as (defaults to root)
#     %% two consecutive % characters are collapsed into a single % character
+
#   %u - expanded to the invoking user's login name
#   The default value is Password:.
+
#   %% - two consecutive % characters are collapsed into a single % character
 +
# The default value is Password:.
  
#Defaults       runas_default
+
#Defaults runas_default
# runas_default: The default user to run commands as if the -u option is not specified on the command line. This defaults to root.
+
# The default user to run commands as if the -u option is not specified on the command line. This defaults to root.
  
#Defaults       syslog_badpri
+
#Defaults syslog_badpri
# syslog_badpri: Syslog priority to use when user authenticates unsuccessfully.  Defaults to alert.
+
# Syslog priority to use when user authenticates unsuccessfully.  Defaults to alert.
#   The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
+
# alert, crit, debug, emerg, err, info, notice, and warning.
  
#Defaults       syslog_goodpri
+
#Defaults syslog_goodpri
# syslog_goodpri: Syslog priority to use when user authenticates successfully.  Defaults to notice.
+
# Syslog priority to use when user authenticates successfully.  Defaults to notice. See syslog_badpri for the priorities.
See syslog_badpri for the list of supported syslog priorities.
+
  
#Defaults       sudoers_locale
+
#Defaults sudoers_locale
# sudoers_locale: Locale to use when parsing the sudoers file, logging commands, and sending email.  Note that changing the locale may affect how sudoers is interpreted.  Defaults to "C".
+
# Locale to use when parsing the sudoers file, logging commands, and sending email.
 +
# Note that changing the locale may affect how sudoers is interpreted.  Defaults to "C".
  
#Defaults       timestampdir
+
#Defaults timestampdir
# timestampdir: The directory in which sudo stores its timestamp files.  The default is /var/db/sudo.
+
# The directory in which sudo stores its timestamp files.  The default is /var/db/sudo.
  
#Defaults       timestampowner
+
#Defaults timestampowner
# timestampowner: The owner of the timestamp directory and the timestamps stored therein.  The default is root.
+
# The owner of the timestamp directory and the timestamps stored therein.  The default is root.
  
#Defaults       env_file
+
#Defaults env_file
# env_file: The env_file option specifies the fully qualified path to a file containing variables to be set in the environment of the program being run.  Entries in this file should either be of the f
+
# The env_file option specifies the fully qualified path to a file containing variables to
quotes.  Variables in this file are subject to other sudo environment settings such as env_keep and env_check.
+
be set in the environment of the program being run.  Entries in this file should either be of the f quotes.
 +
# Variables in this file are subject to other sudo environment settings such as env_keep and env_check.
  
#Defaults       exempt_group
+
#Defaults exempt_group
# exempt_group: Users in this group are exempt from password and PATH requirements.  The group name specified should not include a % prefix.  This is not set by default.
+
# Users in this group are exempt from password and PATH requirements.  The group name specified should not include
 +
a % prefix.  This is not set by default.
  
#Defaults       group_plugin
+
#Defaults group_plugin
# group_plugin: A string containing a sudoers group plugin with optional arguments.  This can be used to implement support for the nonunix_group syntax described earlier.  The string should consist of
+
# A string containing a sudoers group plugin with optional arguments.  This can be used to implement support for the
configuration arguments the plugin requires.  These arguments (if any) will be passed to the plugin's initialization function. If arguments are present, the string must be enclosed in double quot
+
nonunix_group syntax described earlier.  The string should consist of configuration arguments the plugin requires.
For example, given /etc/sudo-group, a group file in Unix group format, the sample group plugin can be used:
+
# These arguments (if any) will be passed to the plugin's initialization function. If arguments are present, the
Defaults group_plugin="sample_group.so /etc/sudo-group"
+
string must be enclosed in double quote For example, given /etc/sudo-group, a group file in Unix group format,
#   For more information see sudo_plugin(5).
+
the sample group plugin can be used: Defaults group_plugin="sample_group.so /etc/sudo-group"
 +
# For more information see sudo_plugin(5).
  
#Defaults       lecture
+
#Defaults lecture
# lecture: This option controls when a short lecture will be printed along with the password prompt.  It has the following possible values:
+
# This option controls when a short lecture will be printed along with the password prompt. The default value is once.
#     always Always lecture the user.
+
# It has the following possible values:
#     never   Never lecture the user.
+
#   always - Always lecture the user.
#     once   Only lecture the user the first time they run sudo.
+
#   never - Never lecture the user.
#   If no value is specified, a value of once is implied.  Negating the option results in a value of never being used.  The default value is once.
+
#    once  - Only lecture the user the first time they run sudo.
 +
# If no value is specified, a value of once is implied.  Negating the option results in a value of never being used.
  
#Defaults       lecture_file
+
#Defaults lecture_file
# lecture_file: Path to a file containing an alternate sudo lecture that will be used in place of the standard lecture if the named file exists.  By default, sudo uses a built-in lecture.
+
# Path to a file containing an alternate sudo lecture that will be used in place of the standard lecture if the named
 +
file exists.  By default, sudo uses a built-in lecture.
  
#Defaults       listpw
+
#Defaults listpw
# listpw: This option controls when a password will be required when a user runs sudo with the -l option.  It has the following possible values:
+
# This option controls when a password will be required when a user runs sudo with the -l option.
#     all     All the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password.
+
# It has the following possible values:
#     always The user must always enter a password to use the -l option.
+
#   all   - All the user's sudoers entries for the current host must have the NOPASSWD set to avoid entering a pass.
#     any     At least one of the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password.
+
#   always - The user must always enter a password to use the -l option.
#     never   The user need never enter a password to use the -l option.
+
#   any   - At least one of the user's sudoers entries for the current host must have the NOPASSWD set to avoid pass.
#   If no value is specified, a value of any is implied.  Negating the option results in a value of never being used.  The default value is any.
+
#   never - The user need never enter a password to use the -l option.
 +
# If no value is specified, a value of any is implied.  The default value is any.
  
#Defaults       logfile
+
#Defaults logfile
# logfile: Path to the sudo log file (not the syslog log file).  Setting a path turns on logging to a file; negating this option turns it off.  By default, sudo logs via syslog.
+
# Path to the sudo log file (not the syslog log file).  Setting a path turns on logging to a file;
 +
negating this option turns it off.  By default, sudo logs via syslog.
  
#Defaults       mailerflags
+
#Defaults mailerflags
# mailerflags: Flags to use when invoking mailer. Defaults to -t.
+
# Flags to use when invoking mailer. Defaults to -t.
  
#Defaults       mailerpath
+
#Defaults mailerpath
# mailerpath: Path to mail program used to send warning mail.  Defaults to the path to sendmail found at configure time.
+
# Path to mail program used to send warning mail.  Defaults to the path to sendmail found at configure time.
  
#Defaults       mailfrom
+
#Defaults mailfrom
# mailfrom: Address to use for the "from" address when sending warning and error mail.  The address should be enclosed in double quotes (") to protect against sudo interpreting the @ sign. Defaults t
+
# Address to use for the "from" address when sending warning and error mail.  The address should
 +
be enclosed in double quotes (") to protect against sudo interpreting the @ sign.
  
#Defaults       mailto
+
#Defaults mailto
# mailto: Address to send warning and error mail to.  The address should be enclosed in double quotes (") to protect against sudo interpreting the @ sign.  Defaults to root.
+
# Address to send warning and error mail to.  The address should be enclosed in double quotes
 +
(") to protect against sudo interpreting the @ sign.  Defaults to root.
  
#Defaults       secure_path
+
#Defaults secure_path
# secure_path: Path used for every command run from sudo.  If you don't trust the people running sudo to have a sane PATH environment variable you may want to use this.  Another use is if you want to
+
# Path used for every command run from sudo.  If you don't trust the people running sudo to have a sane PATH environment
option are not affected by secure_path.  This option is not set by default.
+
variable you may want to use this.  Another use is if you want to option are not affected by secure_path.
 +
# This option is not set by default.
  
#Defaults       syslog
+
#Defaults syslog
# syslog: Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to auth.
+
# Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to auth.
#   The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
+
# authpriv (if OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
  
#Defaults       verifypw
+
#Defaults verifypw
# verifypw: This option controls when a password will be required when a user runs sudo with the -v option.  It has the following possible values:
+
# This option controls when a password will be required when a user runs sudo with the -v option.
#     all     All the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password.
+
# It has the following possible values:
#     always The user must always enter a password to use the -v option.
+
#   all   - All the user's sudoers entries for the current host must have the NOPASSWD flag to avoid pw.
#     any     At least one of the user's sudoers entries for the current host must have the NOPASSWD flag set to avoid entering a password.
+
#   always - The user must always enter a password to use the -v option.
#     never   The user need never enter a password to use the -v option.
+
#   any   - At least one of the user's sudoers entries for the current host must have NOPASSWD to avoid pw.
#   If no value is specified, a value of all is implied.  Negating the option results in a value of never being used.  The default value is all.
+
#   never - The user need never enter a password to use the -v option
 +
# If no value is specified, a value of all is implied.  Negating the option results in a value of never being used.
 +
# The default value is all.
  
#Defaults       env_check
+
#Defaults env_check
# env_check: Environment variables to be removed from the user's environment if the variable's value contains % or / characters.  This can be used to guard against printf-style format vulnerabilities
+
# Environment variables to be removed from the user's environment if the variable's value contains % or / characters.
value without double-quotes.  The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively.  Regardless of whether the env_reset option is ena
+
# This can be used to guard against printf-style format vulnerabilities value without double-quotes.  The list can be
they pass the aforementioned check. The default list of environment variables to check is displayed when sudo is run by root with the -V option.
+
replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively.  Regardless of
 +
whether the env_reset option is ena they pass the aforementioned check. The default list of environment variables
 +
to check is displayed when sudo is run by root with the -V option.
  
#Defaults       env_delete
+
#Defaults env_delete
# env_delete: Environment variables to be removed from the user's environment when the env_reset option is not in effect.  The argument may be a double-quoted, space-separated list or a single value w
+
# Environment variables to be removed from the user's environment when the env_reset option is not in effect.  The
+=, -=, and ! operators respectively.  The default list of environment variables to remove is displayed when sudo is run by root with the -V option. Note that many operating systems will remove p
+
argument may be a double-quoted, space-separated list or a single value w +=, -=, and ! operators respectively.
 +
# The default list of environment variables to remove is displayed when sudo is run by root with the -V option.
  
#Defaults       env_keep
+
#Defaults env_keep
# env_keep: Environment variables to be preserved in the user's environment when the env_reset option is in effect.  This allows fine-grained control over the environment sudo-spawned processes will r
+
# Environment variables to be preserved in the user's environment when the env_reset option is in effect.  This
quotes.  The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively. The default list of variables to keep is displayed when sudo is run by
+
allows fine-grained control over the environment sudo-spawned processes will r quotes.  The list can be replaced,
</nowiki>}}
+
added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively.</nowiki>}}

Revision as of 10:26, 3 October 2013

Template:Article summary start Template:Article summary text Template:Article summary heading Template:Article summary text Template:Article summary end

sudo ("substitute user do") allows a system administrator to delegate authority to give certain users (or groups of users) the ability to run some (or all) commands as root or another user while providing an audit trail of the commands and their arguments.

Rationale

Sudo is an alternative to su for running commands as root. Unlike su, which launches a root shell that allows all further commands root access, sudo instead grants temporary privilege escalation to a single command. By enabling root privileges only when needed, sudo usage reduces the likelyhood that a typo or a bug in an invoked command will ruin the system. Sudo can also be used to run commands as other users; additionally, sudo logs all commands and failed access attempts for security auditing.

Installation

Install the sudo package, available in the official repositories:

# pacman -S sudo

To begin using sudo as a non-privileged user, it must be properly configured. So make sure you read the configuration section.

Usage

With sudo, users can prefix commands with sudo to run them with superuser (or other) privileges.

For example, to use pacman:

$ sudo pacman -Syu

See the sudo manual for more information.

Configuration

View current settings

Run sudo -ll to print out the current sudo configuration.

Using visudo

The configuration file for sudo is /etc/sudoers. It should always be edited with the visudo command. visudo locks the sudoers file, saves edits to a temporary file, and checks that file's grammar before copying it to /etc/sudoers.

Warning: It is imperative that sudoers be free of syntax errors! Any error makes sudo unusable. Always edit it with visudo to prevent errors.

The default editor for visudo is vi. It will be used if you do not specify another editor, by setting either VISUAL or EDITOR environment variables (used in that order) to the desired editor, e.g. vim. The command is run as root:

# VISUAL="/usr/bin/vim -p -X" visudo

You can permanently change the setting for your user to e.g. vim by appending:

export VISUAL="/usr/bin/vim -p -X"

to your ~/.bashrc file. Note that this won't take effect for already-running shells.

To change the editor of choice permanently system-wide only for visudo, add the following line to /etc/sudoers where vim is your prefered editor:

# Reset environment by default
Defaults      env_reset
# Set default EDITOR to vim, and do not allow visudo to use EDITOR/VISUAL.
Defaults      editor="/usr/bin/vim -p -X", !env_editor

Example Entries

To allow a user to gain full root privileges when he/she precedes a command with sudo, add the following line:

USER_NAME   ALL=(ALL) ALL

To allow a user to run all commands as any user but only the machine with hostname HOST_NAME:

USER_NAME   HOST_NAME=(ALL) ALL

To allow members of group wheel sudo access:

%wheel      ALL=(ALL) ALL

To disable asking for a password for user USER_NAME:

Defaults:USER_NAME      !authenticate

Enable explicitly defined commands only for user USER_NAME on host HOST_NAME:

USER_NAME HOST_NAME=/usr/bin/halt,/usr/bin/poweroff,/usr/bin/reboot,/usr/bin/pacman -Syu
Note: the most customized option should go at the end of the file, as the later lines overrides the previous ones. In particular such a line should be after the %wheel line if your user is in this group.

Enable explicitly defined commands only for user USER_NAME on host HOST_NAME without password:

USER_NAME HOST_NAME= NOPASSWD: /usr/bin/halt,/usr/bin/poweroff,/usr/bin/reboot,/usr/bin/pacman -Syu

A detailed sudoers example can be found here. Otherwise, see the sudoers manual for detailed information.

Sudoers default file permissions

The owner and group for the sudoers file must both be 0. The file permissions must be set to 0440. These permissions are set by default, but if you accidentally change them, they should be changed back immediately or sudo will fail.

# chown -c root:root /etc/sudoers
# chmod -c 0440 /etc/sudoers

Password cache timeout

Users may wish to change the default timeout before the cached password expires. This is accomplished with the timestamp_timeout option in /etc/sudoers which is in minutes. Set timeout to 20 minutes.

Defaults:USER_NAME timestamp_timeout=20
Tip: To ensure sudo always asks for a password, set the timeout to 0. To ensure the password never times out, set to less than 0.

Tips and tricks

File example

This example is especially helpful for those using terminal multiplexers like screen, tmux, or ratpoison, and those using sudo from scripts/cronjobs:

/etc/sudoers
Cmnd_Alias WHEELER = /usr/bin/lsof, /bin/nice, /bin/ps, /usr/bin/top, /usr/local/bin/nano, /usr/bin/ss, /usr/bin/locate, /usr/bin/find, /usr/bin/rsync
Cmnd_Alias PROCESSES = /bin/nice, /bin/kill, /usr/bin/nice, /usr/bin/ionice, /usr/bin/top, /usr/bin/kill, /usr/bin/killall, /usr/bin/ps, /usr/bin/pkill
Cmnd_Alias EDITS = /usr/bin/vim, /usr/bin/nano, /usr/bin/cat, /usr/bin/vi
Cmnd_Alias ARCHLINUX = /usr/bin/gparted, /usr/bin/pacman

root ALL = (ALL) ALL
USER_NAME ALL = (ALL) ALL, NOPASSWD: WHEELER, NOPASSWD: PROCESSES, NOPASSWD: ARCHLINUX, NOPASSWD: EDITS
 
Defaults !requiretty, !tty_tickets, !umask
Defaults visiblepw, path_info, insults, lecture=always
Defaults loglinelen = 0, logfile =/var/log/sudo.log, log_year, log_host, syslog=auth
Defaults mailto=webmaster@foobar.com, mail_badpass, mail_no_user, mail_no_perms
Defaults passwd_tries = 8, passwd_timeout = 1
Defaults env_reset, always_set_home, set_home, set_logname
Defaults !env_editor, editor="/usr/bin/vim:/usr/bin/vi:/usr/bin/nano"
Defaults timestamp_timeout=360
Defaults passprompt="Sudo invoked by [%u] on [%H] - Cmd run as %U - Password for user %p:"

Enabling Tab-completion in Bash

Tab-completion, by default, will not work when a user is initially added to the sudoers file. For example, normally john only needs to type:

$ fire<Tab>

and the shell will complete the command for him as:

$ firefox

If, however, john is added to the sudoers file and he types:

$ sudo fire<Tab>

the shell will do nothing.

To enable Tab-completion with sudo, install the bash-completion package from the official repositories. see bash#Tab_completion for more information.

Alternatively, add the following to your ~/.bashrc:

complete -cf sudo

Run X11 apps using sudo

To allow sudo to start graphical application in X11, you need to add:

Defaults env_keep += "HOME"

to visudo.

Disable per-terminal sudo

Warning: This will let any process use your sudo session.

If you are annoyed by sudo's defaults that require you to enter your password every time you open a new terminal, disable tty_tickets:

Defaults !tty_tickets

Environment variables

If you have a lot of environment variables, or you export your proxy settings via export http_proxy="...", when using sudo these variables do not get passed to the root account unless you run sudo with the -E option.

$ sudo -E pacman -Syu

The recommended way of preserving environment variables is to append them to env_keep:

/etc/sudoers
Defaults env_keep += "ftp_proxy http_proxy https_proxy no_proxy"

Passing aliases

If you use a lot of aliases, you might have noticed that they do not carry over to the root account when using sudo. However, there is an easy way to make them work. Simply add the following to your ~/.bashrc or /etc/bash.bashrc:

alias sudo='sudo '

Insults

Users can configure sudo to display clever insults when an incorrect password is entered instead of printing the default "wrong password" message. Find the Defaults line in /etc/sudoers and append "insults" after a comma to existing options. The final result might look like this:

#Defaults specification
Defaults insults

To test, type sudo -K to end the current session and let sudo ask for the password again.

Root password

Users can configure sudo to ask for the root password instead of the user password by adding "rootpw" to the Defaults line in /etc/sudoers:

Defaults timestamp_timeout=0,rootpw

Disable root login

Warning: Arch Linux is not fine-tuned to run with a disabled root account. Users may encounter problems with this method.

With sudo installed and configured, users may wish to disable the root login. Without root, attackers must first guess a user name configured as a sudoer as well as the user password.

Warning: Ensure a user is properly configured as a sudoer before disabling the root account!

The account can be locked via passwd:

# passwd -l root

A similar command unlocks root.

$ sudo passwd -u root

Alternatively, edit /etc/shadow and replace the root's encrypted password with "!":

root:!:12345::::::

To enable root login again:

$ sudo passwd root

kdesu

kdesu may be used under KDE to launch GUI applications with root privileges. It is possible that by default kdesu will try to use su even if the root account is disabled. Fortunately one can tell kdesu to use sudo instead of su. Create/edit the file ~/.kde4/share/config/kdesurc:

[super-user-command]
super-user-command=sudo

PolicyKit

When disabling the root account, it is necessary to change the PolicyKit configuration for local authorization to reflect that. The default is to ask for the root password, so that must be changed. With polkit-1, this can be achieved by editing /etc/polkit-1/localauthority.conf.d/50-localauthority.conf so that AdminIdentities=unix-user:0 is replaced with something else, depending on the system configuration. It can be a list of users and groups, for example:

AdminIdentities=unix-group:wheel

or

AdminIdentities=unix-user:me;unixuser:mom;unix-group:wheel

For more information, see man pklocalauthority.

NetworkManager

Even with the above PolicyKit configuration you still need to configure a policy for NetworkManager. This is documented on the NetworkManager page of this wiki.

Troubleshooting

SSH TTY Issues

SSH does not allocate a tty by default when running a remote command. Without a tty, sudo cannot disable echo when prompting for a password. You can use ssh's -tt option to force it to allocate a tty (or -t twice).

The Defaults option requiretty only allows the user to run sudo if they have a tty.

# Disable "ssh hostname sudo <cmd>", because it will show the password in clear text. You have to run "ssh -t hostname sudo <cmd>".
#
#Defaults    requiretty

Display User Privileges

You can find out what privileges a particular user has with the following command:

$ sudo -lU yourusename

Or view your own with:

$ sudo -l
Matching Defaults entries for yourusename on this host:
    loglinelen=0, logfile=/var/log/sudo.log, log_year, syslog=auth, mailto=webmaster@gmail.com, mail_badpass, mail_no_user, mail_no_perms, env_reset, always_set_home, tty_tickets, lecture=always, pwfeedback, rootpw, set_home

User yourusename may run the following commands on this host:

    (ALL) ALL
    (ALL) NOPASSWD: /usr/bin/lsof, /bin/nice, /usr/bin/ss, /usr/bin/su, /usr/bin/locate, /usr/bin/find, /usr/bin/rsync, /usr/bin/strace,
    (ALL) /bin/nice, /bin/kill, /usr/bin/nice, /usr/bin/ionice, /usr/bin/top, /usr/bin/kill, /usr/bin/killall, /usr/bin/ps, /usr/bin/pkill
    (ALL) /usr/bin/gparted, /usr/bin/pacman
    (ALL) /usr/local/bin/synergyc, /usr/local/bin/synergys
    (ALL) /usr/bin/vim, /usr/bin/nano, /usr/bin/cat
    (root) NOPASSWD: /usr/local/bin/synergyc

Permissive Umask

Sudo will union the user's umask value with its own umask (which defaults to 0022). This prevents sudo from creating files with more open permissions than the user's umask allows. While this is a sane default if no custom umask is in use, this can lead to situations where a utility run by sudo may create files with different permissions than if run by root directly. If errors arise from this, sudo provides a means to fix the umask, even if the desired umask is more permissive than the umask that the user has specified. Adding this (using visudo) will override sudo's default behavior:

Defaults umask = 0022
Defaults umask_override

This sets sudo's umask to root's default umask (0022) and overrides the default behavior, always using the indicated umask regardless of what umask the user as set.


Defaults Skeleton

The authors site has a list of all the options that can be used with the Defaults command in the /etc/sudoers file.

The full list of options (parsed from the version 1.8.7 source code) is below in a format optimized for copying and pasting into your sudoers files for quick editing.

#Defaults always_set_home
#  If enabled, sudo will set the HOME environment variable to the home directory of the target user
#  (which is root unless the -u option is used).  This effectively means that the -H option
#  always_set_home is only effective for configurations where either env_reset is disabled or HOME is present
#  in the env_keep list.  Default: OFF

#Defaults authenticate
#  If set, users must authenticate themselves via a password (or other means of authentication)
#  before they may run commands.  This default may be overridden via the PASSWD and NOPASSWD

#Defaults closefrom_override
#  If set, the user may use sudo's -C option which overrides the default starting
#  point at which sudo begins closing open file descriptors.  Default: OFF

#Defaults compress_io
#  If set, and sudo is configured to log a command's input or output, the I/O logs will be
#  compressed using zlib.  This flag is on by default when sudo is compiled with zlib support.

#Defaults env_editor
#  If set, visudo will use the value of the EDITOR or VISUAL environment variables before falling back on the default
#  editor list.  Note that this may create a security hole as it allows th separated list of editors in the editor
#  variable.  visudo will then only use the EDITOR or VISUAL if they match a value specified in editor.  On by default.

#Defaults env_reset
#  If set, sudo will run the command in a minimal environment containing the TERM, PATH, HOME, MAIL, SHELL, LOGNAME,
#  USER, USERNAME and SUDO_* variables.  Any variables in the caller's env in the file specified by the env_file
#  option (if any).  The default contents of the env_keep and env_check lists are displayed when sudo is run by
#  root with the -V option.

#Defaults fast_glob
#  Normally, sudo uses the glob(3) function to do shell-style globbing when matching path names.
#  However, since it accesses the file system, glob(3) can take a long time to complete for som (automounted).
#  The fast_glob option causes sudo to use the fnmatch(3) function, which does not access the file system to do
#  its matching.  The disadvantage of fast_glob is that it is unable to ma names that include globbing characters
#  are used with the negation operator, '!', as such rules can be trivially bypassed.  As such, this option should
#  not be used when sudoers contains rules that

#Defaults fqdn
#  Set this flag if you want to put fully qualified host names in the sudoers file.  I.e., instead of myhost you
#  would use myhost.mydomain.edu.  You may still use the short form if you wish (and sudo unusable if DNS stops
#  working (for example if the machine is not plugged into the network).  Also note that you must use the
#  host's official name as DNS knows it.  That is, you may not use a all aliases from DNS.  If your machine's
#  host name (as returned by the hostname command) is already fully qualified you shouldn't need to set fqdn.
#  Default: OFF

#Defaults ignore_dot
#  If set, sudo will ignore '.' or '' (current dir) in the PATH environment variable; the PATH
#  itself is not modified.  Default: OFF

#Defaults ignore_local_sudoers
#  If set via LDAP, parsing of /etc/sudoers will be skipped.  This is intended for Enterprises that wish to prevent
#  the usage of local sudoers files so that only LDAP is used.  /etc/sudoers does not even need to exist.
#  Since this option tells sudo how to behave when no specific LDAP entries have been matched, this sudo
#  Option is only meaningful for the cn=default

#Defaults insults
#  If set, sudo will insult users when they enter an incorrect password.  Default: OFF

#Defaults log_host
#  If set, the host name will be logged in the (non-syslog) sudo log file.  Default: OFF

#Defaults log_input
#  If set, sudo will run the command in a pseudo tty and log all user input.  If the standard
#  input is not connected to the user's tty, due to I/O redirection or because the command is part Input is logged
#  to the directory specified by the iolog_dir option (/var/log/sudo-io by default) using a unique session ID that
#  is included in the normal sudo log line, prefixed with TSID=.  Note that user input may contain sensitive
#  information such as passwords (even if they are not echoed to the screen), which will be stored in the log file
#  unencrypted.

#Defaults log_output
#  If set, sudo will run the command in a pseudo tty and log all output that is sent to the
#  screen, similar to the script(1) command.  If the standard output or standard error is not connec is also captured and
#  stored in separate log files. Output is logged to the directory specified by the iolog_dir option (/var/log/sudo-io
#  by default) using a unique session ID that is included in the normal sudo log line, prefixed with TSID=.  The Output
#  logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.

#Defaults log_year
#  If set, the four-digit year will be logged in the (non-syslog) sudo log file.  Default: OFF

#Defaults long_otp_prompt
#  When validating with a One Time Password (OTP) scheme such as S/Key or OPIE, a two-line
#  prompt is used to make it easier to cut and paste the challenge to a local window

#Defaults mail_always
#  Send mail to the mailto user every time a users runs sudo.  Default: OFF

#Defaults mail_badpass
#  Send mail to the mailto user if the user running sudo does not enter the correct password.
#  Default: OFF

#Defaults mail_no_host
#  If set, mail will be sent to the mailto user if the invoking user exists in the sudoers
#  file, but is not allowed to run commands on the current host.  Default: OFF

#Defaults mail_no_perms
#  If set, mail will be sent to the mailto user if the invoking user is allowed to use sudo
#  but the command they are trying is not listed in their sudoers file entry or is explicitly denied

#Defaults mail_no_user
#  If set, mail will be sent to the mailto user if the invoking user is not in the sudoers file.
#  Default: ON

#Defaults noexec
#  If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless overridden
#  by a EXEC tag.  See the description of NOEXEC and EXEC below as well as the "PREVENTING SHE

#Defaults path_info
#  Normally, sudo will tell the user when a command could not be found in their PATH environment
#  variable.  Some sites may wish to disable this as it could be used to gather information on t the executable is
#  simply not in the user's PATH, sudo will tell the user that they are not allowed to run it, which can be confusing.
#  Default: ON

#Defaults passprompt_override
#  The password prompt specified by passprompt will normally only be used if the password prompt provided by
#  systems such as PAM matches the string "Password:"

#Defaults preserve_groups
#  By default, sudo will initialize the group vector to the list of groups the target
#  user is in.  When preserve_groups is set, the user's existing group vector is left unaltered.

#Defaults pwfeedback
#  By default, sudo reads the password like most other Unix programs, by turning off echo
#  until the user hits the return (or enter) key.  Some users become confused by this as it appears to the user
#  presses a key.  Note that this does have a security impact as an onlooker may be able to determine the length of
#  the password being entered.  Default: OFF

#Defaults requiretty
#  If set, sudo will only run when the user is logged in to a real tty.  When this flag is set,
#  sudo can only be run from a login session and not via other means such as cron(8) or cgi-bin

#Defaults root_sudo
#  If set, root is allowed to run sudo too.  Disabling this prevents users from "chaining" sudo
#  commands to get a root shell by doing something like "sudo sudo /bin/sh".  Note, however, that real additional
#  security; it exists purely for historical reasons.  Default: ON

#Defaults rootpw
#  If set, sudo will prompt for the root password instead of the password of the invoking user.
#  Default: OFF

#Defaults runaspw
#  If set, sudo will prompt for the password of the user defined by the runas_default option
#  (defaults to root) instead of the password of the invoking user.  Default: OFF

#Defaults set_home
#  If enabled and sudo is invoked with the -s option the HOME environment variable will be set
#  to the home directory of the target user (which is root unless the -u option is used).  So set_home is only
#  effective for configs where either env_reset is disabled or HOME is present in the env_keep list.  Default: OFF

#Defaults set_logname
#  Normally, sudo will set the LOGNAME, USER and USERNAME environment variables to the name
#  of the target user (usually root unless the -u option is given).  However, since some programs ( may be desirable
#  to change this behavior.  This can be done by negating the set_logname option.  Note that if the env_reset option
#  has not been disabled, entries in the env_keep list will override

#Defaults set_utmp
#  When enabled, sudo will create an entry in the utmp (or utmpx) file when a pseudo-tty is
#  allocated.  A pseudo-tty is allocated by sudo when the log_input, log_output or use_pty flags are e the tty, time,
#  type and pid fields updated.  Default: ON

#Defaults setenv
#  Allow the user to disable the env_reset option from the command line via the -E option.
#  Additionally, environment variables set via the command line are not subject to the restrictions impo variables
#  in this manner.  Default: OFF

#Defaults shell_noargs
#  If set and sudo is invoked with no arguments it acts as if the -s option had been given.
#  That is, it runs a shell as root (the shell is determined by the SHELL environment variable if is off by default.

#Defaults stay_setuid
#  Normally, when sudo executes a command the real and effective UIDs are set to the target
#  user (root by default).  This option changes that behaviour such that the real UID is left as the systems that
#  disable some potentially dangerous functionality when a program is run setuid.  This option is only effective on
#  systems with either the setreuid() or setresuid() function.  This flag

#Defaults targetpw
#  If set, sudo will prompt for the password of the user specified by the -u option (defaults to root) instead
#  of the password of the invoking user.  In addition, the timestamp file name will passwd database as an argument
#  to the -u option.  Default: OFF

#Defaults tty_tickets
#  If set, users must authenticate on a per-tty basis.  With this flag enabled, sudo will
#  use a file named for the tty the user is logged in on in the user's time stamp directory.

#Defaults umask_override
#  If set, sudo will set the umask as specified by sudoers without modification.  This makes
#  it possible to specify a more permissive umask in sudoers than the user's own umask and match user's umask and what
#  is specified in sudoers.  Default: OFF

#Defaults use_pty
#  If set, sudo will run the command in a pseudo-pty even if no I/O logging is being gone.
#  A malicious program run under sudo could conceivably fork a background process that retains to the u that impossible.
#  Default: OFF

#Defaults utmp_runas
#  If set, sudo will store the name of the runas user when updating the utmp (or utmpx) file.
#  By default, sudo stores the name of the invoking user.  Default: OFF

#Defaults visiblepw
#  By default, sudo will refuse to run if the user must enter a password but it is not possible to disable echo on the 
#  terminal. If the visiblepw flag is set, sudo will prompt for a password even when it would be visible on the screen. 
#  This makes it possible to run things like "rsh somehost sudo ls" since rsh(1) does not allocate a tty. Default: OFF

#Defaults closefrom
#  Before it executes a command, sudo will close all open file descriptors other than standard
#  input, standard output and standard error (ie: file descriptors 0-2).

#Defaults passwd_tries
#  The number of tries a user gets to enter his/her password before sudo logs the failure
#  and exits.  The default is 3.

#Defaults loglinelen
#  Number of characters per line for the file log.  This value is used to decide when to wrap
#  lines for nicer log files.  This has no effect on the syslog log file, only the file log.

#Defaults passwd_timeout
#  Number of minutes before the sudo password prompt times out, or 0 for no timeout.
#  The timeout may include a fractional component if minute granularity is insufficient, for example 2

#Defaults timestamp_timeout
#  Number of minutes that can elapse before sudo will ask for a passwd again.  The timeout
#  may include a fractional component if minute granularity is insufficient, for example 2.5. timestamp will never expire.
#  This can be used to allow users to create or delete their own timestamps via sudo -v and sudo -k respectively.

#Defaults umask
#  Umask to use when running the command.  Negate this option or set it to 0777 to preserve
#  the user's umask.  The actual umask that is used will be the union of the user's umask and the value o running
#  a command.  Note on systems that use PAM, the default PAM configuration may specify its own umask which will
#  override the value set in sudoers.

#Defaults badpass_message
#  Message that is displayed if a user enters an incorrect password.  The default is Sorry,
#  try again. unless insults are enabled.

#Defaults editor
#  A colon (':') separated list of editors allowed to be used with visudo.  visudo will choose
#  the editor that matches the user's EDITOR environment variable if possible, or the first editor in

#Defaults iolog_dir
#  The top-level directory to use when constructing the path name for the input/output log
#  directory.  Only used if the log_input or log_output options are enabled or when the LOG_INPUT or L directory.
#  The default is "/var/log/sudo-io". The following percent (%) escape sequences are supported:
#    %{seq}         - expanded to base-36 sequence number, such as 0100A5, to form a new directory, e.g. 01/00/A5
#    %{user}        - expanded to the invoking user's login name
#    %{group}       - expanded to the name of the invoking user's real group ID
#    %{runas_user}  - expanded to the login name of the user the command will be run as (e.g. root)
#    %{runas_group} - expanded to the group name of the user the command will be run as (e.g. wheel)
#    %{hostname}    - expanded to the local host name without the domain name
#    %{command}     - expanded to the base name of the command being run In addition, any escape sequences supported by
#                     strftime() function will be expanded. To include a literal % character, the string %% should be used.

#Defaults iolog_file
#  The path name, relative to iolog_dir, in which to store input/output logs when the log_input or log_output options are
#  enabled or when the LOG_INPUT or LOG_OUTPUT tags are present for a See the iolog_dir option above for a list of
#  supported percent (%) escape sequences. In addition to the escape sequences, path names that end in six or more Xs will
#  have the Xs replaced with a unique combination of digits and letters, similar to the mktemp() function.

#Defaults mailsub
#  Subject of the mail sent to the mailto user. The escape %h will expand to the host name of
#  the machine.  Default is *** SECURITY information for %h ***.

#Defaults noexec_file
#  This option is no longer supported.  The path to the noexec file should now be set in the /etc/sudo.conf file.

#Defaults passprompt
#  The default prompt to use when asking for a password; can be overridden via the -p option or the SUDO_PROMPT
#  environment variable.  The following percent (%) escape sequences are supported:
#    %H - expanded to the local host name including the domain (only if the host name is fqdn or fqdn option is set)
#    %h - expanded to the local host name without the domain name
#    %p - expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags)
#    %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
#  The default value is Password:.

#Defaults runas_default
#  The default user to run commands as if the -u option is not specified on the command line. This defaults to root.

#Defaults syslog_badpri
#  Syslog priority to use when user authenticates unsuccessfully.  Defaults to alert.
#  alert, crit, debug, emerg, err, info, notice, and warning.

#Defaults syslog_goodpri
#  Syslog priority to use when user authenticates successfully.  Defaults to notice. See syslog_badpri for the priorities.

#Defaults sudoers_locale
#  Locale to use when parsing the sudoers file, logging commands, and sending email.
#  Note that changing the locale may affect how sudoers is interpreted.  Defaults to "C".

#Defaults timestampdir
#  The directory in which sudo stores its timestamp files.  The default is /var/db/sudo.

#Defaults timestampowner
#  The owner of the timestamp directory and the timestamps stored therein.  The default is root.

#Defaults env_file
#  The env_file option specifies the fully qualified path to a file containing variables to
#  be set in the environment of the program being run.  Entries in this file should either be of the f quotes.
#  Variables in this file are subject to other sudo environment settings such as env_keep and env_check.

#Defaults exempt_group
#  Users in this group are exempt from password and PATH requirements.  The group name specified should not include
#  a % prefix.  This is not set by default.

#Defaults group_plugin
#  A string containing a sudoers group plugin with optional arguments.  This can be used to implement support for the
#  nonunix_group syntax described earlier.  The string should consist of configuration arguments the plugin requires.
#  These arguments (if any) will be passed to the plugin's initialization function. If arguments are present, the
#  string must be enclosed in double quote For example, given /etc/sudo-group, a group file in Unix group format,
#  the sample group plugin can be used: Defaults group_plugin="sample_group.so /etc/sudo-group"
#  For more information see sudo_plugin(5).

#Defaults lecture
#  This option controls when a short lecture will be printed along with the password prompt.  The default value is once.
#  It has the following possible values:
#    always - Always lecture the user.
#    never  - Never lecture the user.
#    once   - Only lecture the user the first time they run sudo.
#  If no value is specified, a value of once is implied.  Negating the option results in a value of never being used.

#Defaults lecture_file
#  Path to a file containing an alternate sudo lecture that will be used in place of the standard lecture if the named
#  file exists.  By default, sudo uses a built-in lecture.

#Defaults listpw
#  This option controls when a password will be required when a user runs sudo with the -l option.
#  It has the following possible values:
#    all    - All the user's sudoers entries for the current host must have the NOPASSWD set to avoid entering a pass.
#    always - The user must always enter a password to use the -l option.
#    any    - At least one of the user's sudoers entries for the current host must have the NOPASSWD set to avoid pass.
#    never  - The user need never enter a password to use the -l option.
#  If no value is specified, a value of any is implied.  The default value is any.

#Defaults logfile
#  Path to the sudo log file (not the syslog log file).  Setting a path turns on logging to a file;
#  negating this option turns it off.  By default, sudo logs via syslog.

#Defaults mailerflags
#  Flags to use when invoking mailer. Defaults to -t.

#Defaults mailerpath
#  Path to mail program used to send warning mail.  Defaults to the path to sendmail found at configure time.

#Defaults mailfrom
#  Address to use for the "from" address when sending warning and error mail.  The address should
#  be enclosed in double quotes (") to protect against sudo interpreting the @ sign.

#Defaults mailto
#  Address to send warning and error mail to.  The address should be enclosed in double quotes
#  (") to protect against sudo interpreting the @ sign.  Defaults to root.

#Defaults secure_path
#  Path used for every command run from sudo.  If you don't trust the people running sudo to have a sane PATH environment
#  variable you may want to use this.  Another use is if you want to option are not affected by secure_path.
#  This option is not set by default.

#Defaults syslog
#  Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to auth.
#  authpriv (if OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.

#Defaults verifypw
#  This option controls when a password will be required when a user runs sudo with the -v option.
#  It has the following possible values:
#    all    - All the user's sudoers entries for the current host must have the NOPASSWD flag to avoid pw.
#    always - The user must always enter a password to use the -v option.
#    any    - At least one of the user's sudoers entries for the current host must have NOPASSWD to avoid pw.
#    never  - The user need never enter a password to use the -v option
#  If no value is specified, a value of all is implied.  Negating the option results in a value of never being used.
#  The default value is all.

#Defaults env_check
#  Environment variables to be removed from the user's environment if the variable's value contains % or / characters.
#  This can be used to guard against printf-style format vulnerabilities value without double-quotes.  The list can be
#  replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively.  Regardless of
#  whether the env_reset option is ena they pass the aforementioned check. The default list of environment variables
#  to check is displayed when sudo is run by root with the -V option.

#Defaults env_delete
#  Environment variables to be removed from the user's environment when the env_reset option is not in effect.  The
#  argument may be a double-quoted, space-separated list or a single value w +=, -=, and ! operators respectively.
#  The default list of environment variables to remove is displayed when sudo is run by root with the -V option.

#Defaults env_keep
#  Environment variables to be preserved in the user's environment when the env_reset option is in effect.  This
#  allows fine-grained control over the environment sudo-spawned processes will r quotes.  The list can be replaced,
#  added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively.