Man page 5 : sudoers

sudoers - list of which users may execute what

The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).

When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).

The sudoers grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you don't know what EBNF is; it is fairly simple, and the definitions below are annotated.

2.1. Quick guide to EBNF ▲

2.2. Aliases ▲

2.3. Defaults ▲

2.4. User Specification ▲

2.5. Runas_Spec ▲

2.6. SELinux_Spec ▲

2.7. Tag_Spec ▲

2.8. Wildcards ▲

2.9. Exceptions to wildcard rules ▲

2.10. Including other files from within sudoers ▲

2.11. Other special characters and reserved words ▲

sudo's behavior can be modified by \f(CW\*(C`Default_Entry\*(C'\fR lines, as explained earlier. A list of all supported Defaults parameters, grouped by type, are listed below.

Boolean Flags:

always_set_home 16 If enabled, sudo will set the \f(CW\*(C`HOME\*(C'\fR 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 is always implied. Note that \f(CW\*(C`HOME\*(C'\fR is already set when the the env_reset option is enabled, so always_set_home is only effective for configurations where env_reset is disabled. This flag is off by default.

authenticate 16 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 \f(CW\*(C`PASSWD\*(C'\fR and \f(CW\*(C`NOPASSWD\*(C'\fR tags. This flag is on by default.

closefrom_override 16 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.

compress_io 16 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.

env_editor 16 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 the user to run any arbitrary command as root without logging. A safer alternative is to place a colon-separated list of editors in the \f(CW\*(C`editor\*(C'\fR variable. visudo will then only use the EDITOR or VISUAL if they match a value specified in \f(CW\*(C`editor\*(C'\fR. This flag is on by default.

env_reset 16 If set, sudo will reset the environment to only contain the LOGNAME, MAIL, SHELL, USER, USERNAME and the \f(CW\*(C`SUDO_*\*(C'\fR variables. Any variables in the caller's environment that match the \f(CW\*(C`env_keep\*(C'\fR and \f(CW\*(C`env_check\*(C'\fR lists are then added. The default contents of the \f(CW\*(C`env_keep\*(C'\fR and \f(CW\*(C`env_check\*(C'\fR lists are displayed when sudo is run by root with the -V option. If the secure_path option is set, its value will be used for the \f(CW\*(C`PATH\*(C'\fR environment variable. This flag is on by default.

fast_glob 16 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 some patterns, especially when the pattern references a network file system that is mounted on demand (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 match relative path names such as ./ls or ../bin/ls. This has security implications when path names that include globbing characters are used with the negation operator, \f(CW\*(Aq!\*(Aq\fR, as such rules can be trivially bypassed. As such, this option should not be used when sudoers contains rules that contain negated path names which include globbing characters. This flag is off by default.

fqdn 16 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 even mix the two). Beware that turning on fqdn requires sudo to make DNS lookups which may make 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 host alias (\f(CW\*(C`CNAME\*(C'\fR entry) due to performance issues and the fact that there is no way to get all aliases from DNS. If your machine's host name (as returned by the \f(CW\*(C`hostname\*(C'\fR command) is already fully qualified you shouldn't need to set fqdn. This flag is on by default.

ignore_dot 16 If set, sudo will ignore '.' or '' (current dir) in the \f(CW\*(C`PATH\*(C'\fR environment variable; the \f(CW\*(C`PATH\*(C'\fR itself is not modified. This flag is off by default.

ignore_local_sudoers 16 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. This thwarts the efforts of rogue operators who would attempt to add roles to /etc/sudoers. When this option is 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 \f(CW\*(C`cn=defaults\*(C'\fR section. This flag is off by default.

insults 16 If set, sudo will insult users when they enter an incorrect password. This flag is off by default.

log_host 16 If set, the host name will be logged in the (non-syslog) sudo log file. This flag is off by default.

log_year 16 If set, the four-digit year will be logged in the (non-syslog) sudo log file. This flag is off by default.

long_otp_prompt 16 When validating with a One Time Password (OPT) 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 as pretty as the default but some people find it more convenient. This flag is off by default.

mail_always 16 Send mail to the mailto user every time a users runs sudo. This flag is off by default.

mail_badpass 16 Send mail to the mailto user if the user running sudo does not enter the correct password. This flag is off by default.

mail_no_host 16 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.

mail_no_perms 16 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. This flag is off by default.

mail_no_user 16 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.

noexec 16 If set, all commands run via sudo will behave as if the \f(CW\*(C`NOEXEC\*(C'\fR tag has been set, unless overridden by a \f(CW\*(C`EXEC\*(C'\fR tag. See the description of NOEXEC and EXEC below as well as the \*(L"PREVENTING SHELL ESCAPES\*(R" section at the end of this manual. This flag is off by default.

path_info 16 Normally, sudo will tell the user when a command could not be found in their \f(CW\*(C`PATH\*(C'\fR environment variable. Some sites may wish to disable this as it could be used to gather information on the location of executables that the normal user does not have access to. The disadvantage is that if the executable is simply not in the user's \f(CW\*(C`PATH\*(C'\fR, sudo will tell the user that they are not allowed to run it, which can be confusing. This flag is on by default.

passprompt_override 16 The password prompt specified by passprompt will normally only be used if the password prompt provided by systems such as PAM matches the string \*(L"Password:\*(R". If passprompt_override is set, passprompt will always be used. This flag is off by default.

preserve_groups 16 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 real and effective group IDs, however, are still set to match the target user. This flag is off by default.

pwfeedback 16 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 them that sudo has hung at this point. When pwfeedback is set, sudo will provide visual feedback when 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.

requiretty 16 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 scripts. This flag is off by default.

root_sudo 16 If set, root is allowed to run sudo too. Disabling this prevents users from \*(L"chaining\*(R" sudo commands to get a root shell by doing something like \f(CW"sudo sudo /bin/sh"\fR. Note, however, that turning off root_sudo will also prevent root from running sudoedit. Disabling root_sudo provides no real additional security; it exists purely for historical reasons. This flag is on by default.

rootpw 16 If set, sudo will prompt for the root password instead of the password of the invoking user. This flag is off by default.

runaspw 16 If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to \f(CW\*(C`root\*(C'\fR) instead of the password of the invoking user. This flag is off by default.

set_home 16 If enabled and sudo is invoked with the -s option the \f(CW\*(C`HOME\*(C'\fR environment variable will be set to the home directory of the target user (which is root unless the -u option is used). This effectively makes the -s option imply -H. Note that \f(CW\*(C`HOME\*(C'\fR is already set when the the env_reset option is enabled, so set_home is only effective for configurations where env_reset is disabled. This flag is off by default.

set_logname 16 Normally, sudo will set the \f(CW\*(C`LOGNAME\*(C'\fR, \f(CW\*(C`USER\*(C'\fR and \f(CW\*(C`USERNAME\*(C'\fR environment variables to the name of the target user (usually root unless the -u option is given). However, since some programs (including the RCS revision control system) use \f(CW\*(C`LOGNAME\*(C'\fR to determine the real identity of the user, it 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 the value of set_logname. This flag is on by default.

setenv 16 Allow the user to disable the env_reset option from the command line. Additionally, environment variables set via the command line are not subject to the restrictions imposed by env_check, env_delete, or env_keep. As such, only trusted users should be allowed to set variables in this manner. This flag is off by default.

shell_noargs 16 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 \f(CW\*(C`SHELL\*(C'\fR environment variable if it is set, falling back on the shell listed in the invoking user's /etc/passwd entry if not). This flag is off by default.

stay_setuid 16 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 invoking user's UID. In other words, this makes sudo act as a setuid wrapper. This can be useful on 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 is off by default.

targetpw 16 If set, sudo will prompt for the password of the user specified by the -u option (defaults to \f(CW\*(C`root\*(C'\fR) instead of the password of the invoking user. In addition, the timestamp file name will include the target user's name. Note that this flag precludes the use of a uid not listed in the passwd database as an argument to the -u option. This flag is off by default.

log_input 16 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 of a pipeline, that input is also captured and stored in a separate log file. .Sp Input is logged to the /var/log/sudo-io directory using a unique session ID that is included in the normal sudo log line, prefixed with TSID=.

log_output 16 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 connected to the user's tty, due to I/O redirection or because the command is part of a pipeline, that output is also captured and stored in separate log files. .Sp Output is logged to the /var/log/sudo-io directory using a unique session ID that is included in the normal sudo log line, prefixed with TSID=. .Sp Output logs may be viewed with the sudoreplay (8) utility, which can also be used to list or search the available logs.

tty_tickets 16 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 disabled, the time stamp of the directory is used instead. This flag is on by default.

umask_override 16 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 matches historical behavior. If umask_override is not set, sudo will set the umask to be the union of the user's umask and what is specified in sudoers. This flag is off by default.

use_loginclass 16 If set, sudo will apply the defaults specified for the target user's login class if one exists. Only available if sudo is configured with the --with-logincap option. This flag is off by default.

use_pty 16 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 user's terminal device after the main program has finished executing. Use of this option will make that impossible.

visiblepw 16 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 \f(CW"rsh somehost sudo ls"\fR since rsh (1) does not allocate a tty. This flag is off by default.

Integers:

closefrom 16 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 be used to specify a different file descriptor at which to start closing. The default is \f(CW3\fR.

passwd_tries 16 The number of tries a user gets to enter his/her password before sudo logs the failure and exits. The default is \f(CW\*(C`3\*(C'\fR.

Integers that can be used in a boolean context:

loglinelen 16 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 default is \f(CW\*(C`80\*(C'\fR (use 0 or negate the option to disable word wrap).

passwd_timeout 16 Number of minutes before the sudo password prompt times out, or \f(CW0\fR for no timeout. The timeout may include a fractional component if minute granularity is insufficient, for example \f(CW2.5\fR. The default is \f(CW\*(C`0\*(C'\fR.

timestamp_timeout 16 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 \f(CW2.5\fR. The default is \f(CW\*(C`15\*(C'\fR. Set this to \f(CW0\fR to always prompt for a password. If set to a value less than \f(CW0\fR the user's timestamp will never expire. This can be used to allow users to create or delete their own timestamps via \f(CW\*(C`sudo -v\*(C'\fR and \f(CW\*(C`sudo -k\*(C'\fR respectively.

umask 16 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 \f(CW\*(C`0022\*(C'\fR. This guarantees that sudo never lowers the umask when 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.

Strings:

badpass_message 16 Message that is displayed if a user enters an incorrect password. The default is \f(CW\*(C`Sorry, try again.\*(C'\fR unless insults are enabled.

editor 16 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 the list that exists and is executable. The default is \f(CW"/usr/bin/editor"\fR.

mailsub 16 Subject of the mail sent to the mailto user. The escape \f(CW%h\fR will expand to the host name of the machine. Default is \f(CW\*(C`*** SECURITY information for %h ***\*(C'\fR.

noexec_file 16 Path to a shared library containing dummy versions of the execv(), execve() and fexecve() library functions that just return an error. This is used to implement the noexec functionality on systems that support \f(CW\*(C`LD_PRELOAD\*(C'\fR or its equivalent. Defaults to /usr/lib/sudo/sudo_noexec.so.

passprompt 16 The default prompt to use when asking for a password; can be overridden via the -p option or the \f(CW\*(C`SUDO_PROMPT\*(C'\fR environment variable. The following percent (`\f(CW\*(C`%\*(C'\fR') escapes are supported:

%H 4 expanded to the local host name including the domain name (on if the machine's host name is fully qualified or the fqdn option is set)

%h 4 expanded to the local host name without the domain name

%p 4 expanded to the user whose password is being asked for (respects the rootpw, targetpw and runaspw flags in sudoers)

%U 4 expanded to the login name of the user the command will be run as (defaults to root)

%u 4 expanded to the invoking user's login name

\*(C`%%\*(C' 4 two consecutive \f(CW\*(C`%\*(C'\fR characters are collapsed into a single \f(CW\*(C`%\*(C'\fR character
                .Sp The default value is \f(CW\*(C`[sudo] password for %p: \*(C'\fR.

role 16 The default SELinux role to use when constructing a new security context to run the command. The default role may be overridden on a per-command basis in sudoers or via command line options. This option is only available whe sudo is built with SELinux support.

runas_default 16 The default user to run commands as if the -u option is not specified on the command line. This defaults to \f(CW\*(C`root\*(C'\fR. Note that if runas_default is set it must occur before any \f(CW\*(C`Runas_Alias\*(C'\fR specifications.

syslog_badpri 16 Syslog priority to use when user authenticates unsuccessfully. Defaults to \f(CW\*(C`alert\*(C'\fR.

syslog_goodpri 16 Syslog priority to use when user authenticates successfully. Defaults to \f(CW\*(C`notice\*(C'\fR.

sudoers_locale 16 Locale to use when parsing the sudoers file. Note that changing the locale may affect how sudoers is interpreted. Defaults to \f(CW"C"\fR.

timestampdir 16 The directory in which sudo stores its timestamp files. The default is /var/lib/sudo.

timestampowner 16 The owner of the timestamp directory and the timestamps stored therein. The default is \f(CW\*(C`root\*(C'\fR.

type 16 The default SELinux type to use when constructing a new security context to run the command. The default type may be overridden on a per-command basis in sudoers or via command line options. This option is only available whe sudo is built with SELinux support.

Strings that can be used in a boolean context:

askpass 12 The askpass option specifies the fully qualified path to a helper program used to read the user's password when no terminal is available. This may be the case when sudo is executed from a graphical (as opposed to text-based) application. The program specified by askpass should display the argument passed to it as the prompt and write the user's password to the standard output. The value of askpass may be overridden by the \f(CW\*(C`SUDO_ASKPASS\*(C'\fR environment variable.

env_file 12 The env_file options 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 form \f(CW\*(C`VARIABLE=value\*(C'\fR or \f(CW\*(C`export VARIABLE=value\*(C'\fR. The value may optionally be surrounded by single or double quotes. Variables in this file are subject to other sudo environment settings such as env_keep and env_check.

exempt_group 12 Users in this group are exempt from password and PATH requirements. This is not set by default.

lecture 12 This option controls when a short lecture will be printed along with the password prompt. It has the following possible values:

always 8 Always lecture the user.

never 8 Never lecture the user.

once 8 Only lecture the user the first time they run sudo.
            .Sp 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.

lecture_file 12 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.

listpw 12 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 8 All the user's sudoers entries for the current host must have the \f(CW\*(C`NOPASSWD\*(C'\fR flag set to avoid entering a password.

always 8 The user must always enter a password to use the -l option.

any 8 At least one of the user's sudoers entries for the current host must have the \f(CW\*(C`NOPASSWD\*(C'\fR flag set to avoid entering a password.

never 8 The user need never enter a password to use the -l option.
            .Sp 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.

logfile 12 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.

mailerflags 12 Flags to use when invoking mailer. Defaults to -t.

mailerpath 12 Path to mail program used to send warning mail. Defaults to the path to sendmail found at configure time.

mailfrom 12 Address to use for the \*(L"from\*(R" address when sending warning and error mail. The address should be enclosed in double quotes (\f(CW\*(C`"\*(C'\fR) to protect against sudo interpreting the \f(CW\*(C`@\*(C'\fR sign. Defaults to the name of the user running sudo.

mailto 12 Address to send warning and error mail to. The address should be enclosed in double quotes (\f(CW\*(C`"\*(C'\fR) to protect against sudo interpreting the \f(CW\*(C`@\*(C'\fR sign. Defaults to \f(CW\*(C`root\*(C'\fR.

secure_path 12 Path used for every command run from sudo. If you don't trust the people running sudo to have a sane \f(CW\*(C`PATH\*(C'\fR environment variable you may want to use this. Another use is if you want to have the \*(L"root path\*(R" be separate from the \*(L"user path.\*(R" Users in the group specified by the exempt_group option are not affected by secure_path. This option is set to F</usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/X11R6/bin> by default.

syslog 12 Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to \f(CW\*(C`authpriv\*(C'\fR.

verifypw 12 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 8 All the user's sudoers entries for the current host must have the \f(CW\*(C`NOPASSWD\*(C'\fR flag set to avoid entering a password.

always 8 The user must always enter a password to use the -v option.

any 8 At least one of the user's sudoers entries for the current host must have the \f(CW\*(C`NOPASSWD\*(C'\fR flag set to avoid entering a password.

never 8 The user need never enter a password to use the -v option.
            .Sp 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.

Lists that can be used in a boolean context:

env_check 16 Environment variables to be removed from the user's environment if the variable's value contains \f(CW\*(C`%\*(C'\fR or \f(CW\*(C`/\*(C'\fR characters. This can be used to guard against printf-style format vulnerabilities in poorly-written programs. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the \f(CW\*(C`=\*(C'\fR, \f(CW\*(C`+=\*(C'\fR, \f(CW\*(C`-=\*(C'\fR, and \f(CW\*(C`!\*(C'\fR operators respectively. Regardless of whether the \f(CW\*(C`env_reset\*(C'\fR option is enabled or disabled, variables specified by \f(CW\*(C`env_check\*(C'\fR will be preserved in the environment if 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.

env_delete 16 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 without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the \f(CW\*(C`=\*(C'\fR, \f(CW\*(C`+=\*(C'\fR, \f(CW\*(C`-=\*(C'\fR, and \f(CW\*(C`!\*(C'\fR 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 potentially dangerous variables from the environment of any setuid process (such as sudo).

env_keep 16 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 receive. The argument may be a double-quoted, space-separated list or a single value without double-quotes. The list can be replaced, added to, deleted from, or disabled by using the \f(CW\*(C`=\*(C'\fR, \f(CW\*(C`+=\*(C'\fR, \f(CW\*(C`-=\*(C'\fR, and \f(CW\*(C`!\*(C'\fR operators respectively. The default list of variables to keep is displayed when sudo is run by root with the -V option.

When logging via syslog (3), sudo accepts the following values for the syslog facility (the value of the syslog Parameter): authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7. The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.

/etc/sudoers 24 List of who can run what

/etc/group 24 Local groups file

/etc/netgroup 24 List of network groups

/var/log/sudo-io 24 I/O log files

Below are example sudoers entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases:

# Run X applications through sudo; HOME is used to find the # .Xauthority file. Note that other programs use HOME to find # configuration files and this may lead to privilege escalation! Defaults env_keep += "DISPLAY HOME" # User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBMASTERS = will, wendy, wim # Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase Runas_Alias ADMINGRP = adm, oper # Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 128.138.0.0/255.255.0.0 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0 Host_Alias SERVERS = master, mail, www, ns Host_Alias CDROM = orion, perseus, hercules # Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh, \ /usr/local/bin/tcsh, /usr/bin/rsh, \ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less

Here we override some of the compiled in default values. We want sudo to log via syslog (3) using the auth facility in all cases. We don't want to subject the full time staff to the sudo lecture, user millert need not give a password, and we don't want to reset the \f(CW\*(C`LOGNAME\*(C'\fR, \f(CW\*(C`USER\*(C'\fR or \f(CW\*(C`USERNAME\*(C'\fR environment variables when running commands as root. Additionally, on the machines in the SERVERS \f(CW\*(C`Host_Alias\*(C'\fR, we keep an additional local log file and make sure we log the year in each log line since the log entries will be kept around for several years. Lastly, we disable shell escapes for the commands in the PAGERS \f(CW\*(C`Cmnd_Alias\*(C'\fR (/usr/bin/more, /usr/bin/pg and /usr/bin/less).

# Override built-in defaults Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec

The User specification is the part that actually determines who may run what.

root ALL = (ALL) ALL %wheel ALL = (ALL) ALL

We let root and any user in group wheel run any command on any host as any user.

FULLTIMERS ALL = NOPASSWD: ALL

Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves.

PARTTIMERS ALL = ALL

Part time sysadmins (bostley, jwfox, and crawl) may run any command on any host but they must authenticate themselves first (since the entry lacks the \f(CW\*(C`NOPASSWD\*(C'\fR tag).

jack CSNETS = ALL

The user jack may run any command on the machines in the CSNETS alias (the networks \f(CW128.138.243.0\fR, \f(CW128.138.204.0\fR, and \f(CW128.138.242.0\fR). Of those networks, only \f(CW128.138.204.0\fR has an explicit netmask (in CIDR notation) indicating it is a class C network. For the other networks in CSNETS, the local machine's netmask will be used during matching.

lisa CUNETS = ALL

The user lisa may run any command on any host in the CUNETS alias (the class B network \f(CW128.138.0.0\fR).

operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/

The operator user may run commands limited to simple maintenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory /usr/oper/bin/.

joe ALL = /usr/bin/su operator

The user joe may only su (1) to operator.

pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd root %opers ALL = (: ADMINGRP) /usr/sbin/

Users in the opers group may run commands in /usr/sbin/ as themselves with any group in the ADMINGRP \f(CW\*(C`Runas_Alias\*(C'\fR (the adm and oper groups).

The user pete is allowed to change anyone's password except for root on the HPPA machines. Note that this assumes passwd (1) does not take multiple user names on the command line.

bob SPARC = (OP) ALL : SGI = (OP) ALL

The user bob may run anything on the SPARC and SGI machines as any user listed in the OP \f(CW\*(C`Runas_Alias\*(C'\fR (root and operator).

jim +biglab = ALL

The user jim may run any command on machines in the biglab netgroup. sudo knows that \*(L"biglab\*(R" is a netgroup due to the '+' prefix.

+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser

Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on all machines.

fred ALL = (DB) NOPASSWD: ALL

The user fred can run commands as any user in the DB \f(CW\*(C`Runas_Alias\*(C'\fR (oracle or sybase) without giving a password.

john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*

On the ALPHA machines, user john may su to anyone except root but he is not allowed to specify any options to the su (1) command.

jen ALL, !SERVERS = ALL

The user jen may run any command on any machine except for those in the SERVERS \f(CW\*(C`Host_Alias\*(C'\fR (master, mail, www and ns).

jill SERVERS = /usr/bin/, !SU, !SHELLS

For any machine in the SERVERS \f(CW\*(C`Host_Alias\*(C'\fR, jill may run any commands in the directory /usr/bin/ except for those commands belonging to the SU and SHELLS \f(CW\*(C`Cmnd_Aliases\*(C'\fR.

steve CSNETS = (operator) /usr/local/op_commands/

The user steve may run any command in the directory /usr/local/op_commands/ but only as user operator.

matt valkyrie = KILL

On his personal workstation, valkyrie, matt needs to be able to kill hung processes.

WEBMASTERS www = (www) ALL, (root) /usr/bin/su www

On the host www, any user in the WEBMASTERS \f(CW\*(C`User_Alias\*(C'\fR (will, wendy, and wim), may run any command as user www (which owns the web pages) or simply su (1) to www.

ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM

Any user may mount or unmount a CD-ROM on the machines in the CDROM \f(CW\*(C`Host_Alias\*(C'\fR (orion, perseus, hercules) without entering a password. This is a bit tedious for users to type, so it is a prime candidate for encapsulating in a shell script.

It is generally not effective to \*(L"subtract\*(R" commands from \f(CW\*(C`ALL\*(C'\fR using the '!' operator. A user can trivially circumvent this by copying the desired command to a different name and then executing that. For example:

bill ALL = ALL, !SU, !SHELLS

Doesn't really prevent bill from running the commands listed in SU or SHELLS since he can simply copy those commands to a different name, or use a shell escape from an editor or other program. Therefore, these kind of restrictions should be considered advisory at best (and reinforced by policy).

Furthermore, if the fast_glob option is in use, it is not possible to reliably negate commands where the path name includes globbing (aka wildcard) characters. This is because the C library's fnmatch (3) function cannot resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it can result in a security issue for rules that subtract or revoke privileges.

For example, given the following sudoers entry:

john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*, /usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root

User john can still run \f(CW\*(C`/usr/bin/passwd root\*(C'\fR if fast_glob is enabled by changing to /usr/bin and running \f(CW\*(C`./passwd root\*(C'\fR instead.

Once sudo executes a program, that program is free to do whatever it pleases, including run other programs. This can be a security issue since it is not uncommon for a program to allow shell escapes, which lets a user bypass sudo's access control and logging. Common programs that permit shell escapes include shells (obviously), editors, paginators, mail and terminal programs.

There are two basic approaches to this problem:

restrict 10 Avoid giving users access to commands that allow the user to run arbitrary commands. Many editors have a restricted mode where shell escapes are disabled, though sudoedit is a better solution to running editors via sudo. Due to the large number of programs that offer shell escapes, restricting users to the set of programs that do not if often unworkable.

noexec 10 Many systems that support shared libraries have the ability to override default library functions by pointing an environment variable (usually \f(CW\*(C`LD_PRELOAD\*(C'\fR) to an alternate shared library. On such systems, sudo's noexec functionality can be used to prevent a program run by sudo from executing any other programs. Note, however, that this applies only to native dynamically-linked executables. Statically-linked executables and foreign executables running under binary emulation are not affected. .Sp To tell whether or not sudo supports noexec, you can run the following as root: .Sp sudo -V | grep "dummy exec"

.Sp If the resulting output contains a line that begins with: .Sp File containing dummy exec functions:

.Sp then sudo may be able to replace the exec family of functions in the standard library with its own that simply return an error. Unfortunately, there is no foolproof way to know whether or not noexec will work at compile-time. noexec should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known not to work on AIX and UnixWare. noexec is expected to work on most operating systems that support the \f(CW\*(C`LD_PRELOAD\*(C'\fR environment variable. Check your operating system's manual pages for the dynamic linker (usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see if \f(CW\*(C`LD_PRELOAD\*(C'\fR is supported. .Sp To enable noexec for a command, use the \f(CW\*(C`NOEXEC\*(C'\fR tag as documented in the User Specification section above. Here is that example again: .Sp aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi

.Sp This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting noexec you can always just try it out and see if it works.

Note that restricting shell escapes is not a panacea. Programs running as root are still capable of many potentially hazardous operations (such as changing or overwriting files) that could lead to unintended privilege escalation. In the specific case of an editor, a safer approach is to give the user permission to run sudoedit.

rsh (1), su (1), fnmatch (3), glob (3), sudo (8), visudo (8)

The sudoers file should always be edited by the visudo command which locks the file and does grammatical checking. It is imperative that sudoers be free of syntax errors since sudo will not run with a syntactically incorrect sudoers file.

When using netgroups of machines (as opposed to users), if you store fully qualified host name in the netgroup (as is usually the case), you either need to have the machine's host name be fully qualified as returned by the \f(CW\*(C`hostname\*(C'\fR command or use the fqdn option in sudoers.

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

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