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 are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with “wildcard” characters, which have different meanings.
?*+Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name).
User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias.
Alias ::= 'User_Alias' User_Alias (':' User_Alias)* |
'Runas_Alias' Runas_Alias (':' Runas_Alias)* |
'Host_Alias' Host_Alias (':' Host_Alias)* |
'Cmnd_Alias' Cmnd_Alias (':' Cmnd_Alias)*
User_Alias ::= NAME '=' User_List
Runas_Alias ::= NAME '=' Runas_List
Host_Alias ::= NAME '=' Host_List
Cmnd_Alias ::= NAME '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and underscore characters (‘_’). A NAME must start with an uppercase letter. It is possible to put several alias definitions of the same type on a single line, joined by a colon (‘:’). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user ids (prefixed with ‘#’), system group names and ids (prefixed with ‘%’ and ‘%#’ respectively), netgroups (prefixed with ‘+’), non-Unix group names and IDs (prefixed with ‘%:’ and ‘%:#’ respectively) and User_Aliases. Each list item may be prefixed with zero or more ‘!’ operators. An odd number of ‘!’ operators negate the value of the item; an even number just cancel each other out.
A user name, uid, group, gid, netgroup, nonunix_group or nonunix_gid may be enclosed in double quotes to avoid the need for escaping special characters. Alternately, special characters may be specified in escaped hex mode, e.g. \x20 for space. When using double quotes, any prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying implementation. For instance, the QAS AD backend supports the following formats:
Note that quotes around group names are optional. Unquoted strings must use a backslash (‘\’) to escape spaces and special characters. See Other special characters and reserved words for a list of characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias
A Runas_List is similar to a User_List except that instead of User_Aliases it can contain Runas_Aliases. Note that user names and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are considered to be distinct. If you wish to match all user names with the same uid (e.g. root and toor), you can use a uid instead (#0 in the example given).
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias
A Host_List is made up of one or more host names, IP addresses, network numbers, netgroups (prefixed with ‘+’) and other aliases. Again, the value of an item may be negated with the ‘!’ operator. If you do not specify a netmask along with the network number, sudo will query each of the local host's network interfaces and, if the network number corresponds to one of the hosts's network interfaces, the corresponding netmask will be used. The netmask may be specified either in standard IP address notation (e.g. 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation (number of bits, e.g. 24 or 64). A host name may include shell-style wildcards (see the Wildcards section below), but unless the host name command on your machine returns the fully qualified host name, you'll need to use the fqdn option for wildcards to be useful. Note that sudo only inspects actual network interfaces; this means that IP address 127.0.0.1 (localhost) will never match. Also, the host name “localhost” will only match if that is the actual host name, which is usually only the case for non-networked systems.
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Cmnd ::= '!'* command name |
'!'* directory |
'!'* "sudoedit" |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more command names, directories, and other aliases. A command name is a fully qualified file name which may include shell-style wildcards (see the Wildcards section below). A simple file name allows the user to run the command with any arguments he/she wishes. However, you may also specify command line arguments (including wildcards). Alternately, you can specify "" to indicate that the command may only be run without command line arguments. A directory is a fully qualified path name ending in a ‘/’. When you specify a directory in a Cmnd_List, the user will be able to run any file within that directory (but not in any sub-directories therein).
If a Cmnd has associated command line arguments, then the arguments in the Cmnd must match exactly those given by the user on the command line (or match the wildcards if there are any). Note that the following characters must be escaped with a ‘\’ if they are used in command arguments: ‘,’, ‘:’, ‘=’, ‘\’. The special command “sudoedit” is used to permit a user to run sudo with the ‑e option (or as sudoedit). It may take command line arguments just as a normal command does.
Default_Entry lines. These may affect all users on any host, all users on a specific host, a specific user, a specific command, or commands being run as a specific user. Note that per-command entries may not include command line arguments. If you need to specify arguments, define a Cmnd_Alias and reference that instead.
Default_Type ::= 'Defaults' |
'Defaults' '@' Host_List |
'Defaults' ':' User_List |
'Defaults' '!' Cmnd_List |
'Defaults' '>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are implicitly boolean and can be turned off via the ‘!’ operator. Some integer, string and list parameters may also be used in a boolean context to disable them. Values may be enclosed in double quotes ("") when they contain multiple words. Special characters may be escaped with a backslash (‘\’).
Lists have two additional assignment operators, += and -=. These operators are used to add to and delete from a list respectively. It is not an error to use the -= operator to remove an element that does not exist in a list.
Defaults entries are parsed in the following order: generic, host and user Defaults first, then runas Defaults and finally command defaults.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? SELinux_Spec? Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
SELinux_Spec ::= ('ROLE=role' | 'TYPE=type')
Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:' |
'SETENV:' | 'NOSETENV:' | 'LOG_INPUT:' | 'NOLOG_INPUT:' |
'LOG_OUTPUT:' | 'NOLOG_OUTPUT:')
A user specification determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as root, but this can be changed on a per-command basis.
The basic structure of a user specification is “who where = (as_whom) what”. Let's break that down into its constituent parts:
Runas_Spec determines the user and/or the group that a command may be run as. A fully-specified Runas_Spec consists of two Runas_Lists (as defined above) separated by a colon (‘:’) and enclosed in a set of parentheses. The first Runas_List indicates which users the command may be run as via sudo's ‑u option. The second defines a list of groups that can be specified via sudo's ‑g option. If both Runas_Lists are specified, the command may be run with any combination of users and groups listed in their respective Runas_Lists. If only the first is specified, the command may be run as any user in the list but no ‑g option may be specified. If the first Runas_List is empty but the second is specified, the command may be run as the invoking user with the group set to any listed in the Runas_List. If no Runas_Spec is specified the command may be run as root and no group may be specified.
A Runas_Spec sets the default for the commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm—but only as operator. E.g.,
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
Note that while the group portion of the Runas_Spec permits the user to run as command with that group, it does not force the user to do so. If no group is specified on the command line, the command will run with the group listed in the target user's password database entry. The following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls $ sudo -u operator -g operator /bin/ls $ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
Note that in this example only the group will be set, the command still runs as user tcm. E.g.
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in which case the user may select any combination of users and groups via the ‑u and ‑g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally setting the group to operator or system.
NOPASSWD, PASSWD, NOEXEC, EXEC, SETENV, NOSETENV, LOG_INPUT, NOLOG_INPUT, LOG_OUTPUT and NOLOG_OUTPUT. Once a tag is set on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless it is overridden by the opposite tag (in other words, PASSWD overrides NOPASSWD and NOEXEC overrides EXEC).
NOPASSWD and PASSWD
By default, sudo requires that a user authenticate him or herself before running a command. This behavior can be modified via the NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a default for the commands that follow it in the Cmnd_Spec_List. Conversely, the PASSWD tag can be used to reverse things. For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on the machine rushmore without authenticating himself. If we only want ray to be able to run /bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are in the group specified by the exempt_group option.
By default, if the NOPASSWD tag is applied to any of the entries for a user on the current host, he or she will be able to run “sudo -l” without a password. Additionally, a user may only run “sudo -v” without a password if the NOPASSWD tag is present for all a user's entries that pertain to the current host. This behavior may be overridden via the verifypw and listpw options.
NOEXEC and EXEC
If sudo has been compiled with noexec support and the underlying operating system supports it, the NOEXEC tag can be used to prevent a dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the Preventing shell escapes section below for more details on how NOEXEC works and whether or not it will work on your system.
SETENV and NOSETENV
These tags override the value of the setenv option on a per-command basis. Note that if SETENV has been set for a command, the user may disable the env_reset option from the command line via the ‑E option. Additionally, environment variables set on 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. If the command matched is ALL, the SETENV tag is implied for that command; this default may be overridden by use of the NOSETENV tag.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input option on a per-command basis. For more information, see the description of log_input in the SUDOERS OPTIONS section below.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output option on a per-command basis. For more information, see the description of log_output in the SUDOERS OPTIONS section below.
*?[...][!...]\x*’, ‘?’, ‘[’, and ‘]’.POSIX character classes may also be used if your system's glob(3) and fnmatch(3) functions support them. However, because the ‘:’ character has special meaning in sudoers, it must be escaped. For example:
/bin/ls [[:alpha:]]*
Would match any file name beginning with a letter.
Note that a forward slash (‘/’) will not be matched by wildcards used in the path name. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.
Wildcards in command line arguments should be used with care. Because command line arguments are matched as a single, concatenated string, a wildcard such as ‘?’ or ‘*’ can match multiple words. For example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended.
"""" is the only command line argument in the sudoers entry it means that command is not allowed to be run with any arguments./’) will not be matched by a wildcard.#include and #includedir directives.
This can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers will be /etc/sudoers and the per-machine one will be /etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers we would use the following line in /etc/sudoers:
#include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the current file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching the end of /etc/sudoers.local, the rest of /etc/sudoers will be processed. Files that are included may themselves include other files. A hard limit of 128 nested include files is enforced to prevent include file loops.
If the path to the include file is not fully-qualified (does not begin with a ‘/’, it must be located in the same directory as the sudoers file it was included from. For example, if /etc/sudoers contains the line:
#include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the %h escape, signifying the short form of the host name. In other words, if the machine's host name is “xerxes”, then
#include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes.
The #includedir directive can be used to create a sudo.d directory that the system package manager can drop sudoers rules into as part of package installation. For example, given:
#includedir /etc/sudoers.d
sudo will read each file in /etc/sudoers.d, skipping file names that end in ‘~’ or contain a ‘.’ character to avoid causing problems with package manager or editor temporary/backup files. Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second. Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second. Using a consistent number of leading zeroes in the file names can be used to avoid such problems.
Note that unlike files included via #include, visudo will not edit the files in a #includedir directory unless one of them contains a syntax error. It is still possible to run visudo with the ‑f flag to edit the files directly.
#’) is used to indicate a comment (unless it is part of a #include directive or unless it occurs in the context of a user name and is followed by one or more digits, in which case it is treated as a uid). Both the comment character and any text after it, up to the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. You should not try to define your own alias called ALL as the built-in alias will be used in preference to your own. Please note that using ALL can be dangerous since in a command context, it allows the user to run any command on the system.
An exclamation point (‘!’) can be used as a logical not operator both in an alias and in front of a Cmnd. This allows one to exclude certain values. Note, however, that using a ‘!’ in conjunction with the built-in ALL alias to allow a user to run “all but a few” commands rarely works as intended (see SECURITY NOTES below).
Long lines can be continued with a backslash (‘\’) as the last character on the line.
White space between elements in a list as well as special syntactic characters in a User Specification (‘=’, ‘:’, ‘(’, ‘)’) is optional.
The following characters must be escaped with a backslash (‘\’) when used as part of a word (e.g. a user name or host name): ‘!’, ‘=’, ‘:’, ‘,’, ‘(’, ‘)’, ‘\’.
Default_Entry lines, as explained earlier. A list of all supported Defaults parameters, grouped by type, are listed below.
Boolean Flags:
PASSWD and NOPASSWD tags. This flag is on by default.editor variable. visudo will then only use the EDITOR or VISUAL if they match a value specified in editor. This flag is off by default.env_keep and env_check lists are then added, followed by any variables present 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 option is set, its value will be used for the PATH environment variable. This flag is on by default.!’, 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.hostname command) does not contain the domain name. In other words, instead of myhost you would use myhost.mydomain.edu. You may still use the short form if you wish (and even mix the two). This option is only effective when the “canonical” host name, as returned by the getaddrinfo() or gethostbyname() function, is a fully-qualified domain name. This is usually the case when the system is configured to use DNS for host name resolution.
If the system is configured to use the /etc/hosts file in preference to DNS, the “canonical” host name may not be fully-qualified. The order that sources are queried for hosts name resolution is usually specified in the /etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf, or, in some cases, /etc/resolv.conf file. In the /etc/hosts file, the first host name of the entry is considered to be the “canonical” name; subsequent names are aliases that are not used by sudoers. For example, the following hosts file line for the machine “xyzzy” has the fully-qualified domain name as the “canonical” host name, and the short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
Beware that when using DNS for host name resolution, turning on fqdn requires sudoers to make DNS lookups which renders sudo unusable if DNS stops working (for example if the machine is disconnected from the network). Also note that just like with the hosts file, you must use the “canonical” name as DNS knows it. That is, you may not use a host alias (CNAME entry) due to performance issues and the fact that there is no way to get all aliases from DNS.
This flag is off by default.
cn=defaults section. This flag is off by default.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. In most cases, logging the command output via log_output is all that is required.
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=”.
Output logs may be viewed with the sudoreplay(8) utility, which can also be used to list or search the available logs.
NOEXEC tag has been set, unless overridden by a EXEC tag. See the description of NOEXEC and EXEC below as well as the Preventing shell escapes section at the end of this manual. This flag is off by default.sudo sudo /bin/sh”. 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.root) instead of the password of the invoking user. This flag is off by default.root) instead of the password of the invoking user. In addition, the time stamp 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.--with-logincap option. This flag is off by default.ssh somehost sudo ls” since by default, ssh(1) does not allocate a tty when running a command. This flag is off by default.Integers:
3.3.Integers that can be used in a boolean context:
80 (use 0 or negate the option to disable word wrap).0 for no timeout. The timeout may include a fractional component if minute granularity is insufficient, for example 2.5. The default is 5.2.5. The default is 5. Set this to 0 to always prompt for a password. If set to a value less than 0 the user's time stamp will never expire. This can be used to allow users to create or delete their own time stamps via “sudo -v” and “sudo -k” respectively.0022. 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:
Sorry, try again. unless insults are enabled.:’) 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 vi.LOG_INPUT or LOG_OUTPUT tags are present for a command. The default is /var/log/sudo-io.%h will expand to the host name of the machine. Default is “*** SECURITY information for %h ***”.%’) escape sequences are supported:
%H%h%p%U%u%%% characters are collapsed into a single % characterThe default value is “Password:”.
root.alert.
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, and warning.
notice.
See syslog_badpri for the list of supported syslog priorities.
C”.root.Strings that can be used in a boolean context:
VARIABLE=value” or “export VARIABLE=value”. 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.% prefix. This is not set by default.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.
NOPASSWD flag set to avoid entering a password.NOPASSWD flag set to avoid entering a password.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.
@ sign. Defaults to the name of the user running sudo.@ sign. Defaults to root.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.
NOPASSWD flag set to avoid entering a password.NOPASSWD flag set to avoid entering a password.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:
%’ or ‘/’ 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 =, +=, -=, and ! operators respectively. Regardless of whether the env_reset option is enabled or disabled, variables specified by env_check 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.=, +=, -=, 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 potentially dangerous variables from the environment of any setuid process (such as sudo).=, +=, -=, and ! operators respectively. The default list of variables to keep is displayed when sudo is run by root with the ‑V option.
Defaults env_keep += "DISPLAY HOME"
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBMASTERS = will, wendy, wim
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
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 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 LOGNAME, USER or USERNAME environment variables when running commands as root. Additionally, on the machines in the SERVERS Host_Alias, 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 Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less).
Defaults syslog=auth Defaults>root !set_logname Defaults:FULLTIMERS !lecture Defaults:millert !authenticate Defaults@SERVERS 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 NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias (the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those networks, only 128.138.204.0 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 128.138.0.0).
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 Runas_Alias (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 Runas_Alias (root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup. sudo knows that “biglab” 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 Runas_Alias (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 Host_Alias (master, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in the directory /usr/bin/ except for those commands belonging to the SU and SHELLS Cmnd_Aliases.
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 User_Alias (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 Host_Alias (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.
!’ 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).
In general, if a user has sudo ALL there is nothing to prevent them from creating their own program that gives them a root shell (or making their own copy of a shell) regardless of any ‘!’ elements in the user specification.
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 /usr/bin/passwd root if fast_glob is enabled by changing to /usr/bin and running ./passwd root instead.
There are two basic approaches to this problem:
The noexec feature is known to work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, HP-UX 11.x and AIX 5.3 and above. It should be supported on most operating systems that support the LD_PRELOAD 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 LD_PRELOAD is supported.
On Solaris 10 and higher, noexec uses Solaris privileges instead of the LD_PRELOAD environment variable.
To enable noexec for a command, use the NOEXEC tag as documented in the User Specification section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
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 check whether shell escapes work when noexec is enabled.
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.
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 hostname command or use the fqdn option in sudoers.