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 conflicting values, 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 (\s-1EBNF\s0). Don't despair if you don't know what \s-1EBNF\s0 is; it is fairly simple, and the definitions below are annotated.

\s-1EBNF\s0 is a concise and exact way of describing the grammar of a language. Each \s-1EBNF\s0 definition is made up of production rules. E.g.,

symbol ::= definition | alternate1 | alternate2 ...

Each production rule references others and thus makes up a grammar for the language. \s-1EBNF\s0 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. Means that the preceding symbol (or group of symbols) is optional. That is, it may appear once or not at all. Means that the preceding symbol (or group of symbols) may appear zero or more times. Means that the preceding symbol (or group of symbols) may appear one or more times.

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).

There are four kinds of aliases: CWUser_Alias, CWRunas_Alias, CWHost_Alias and CWCmnd_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][A-Z][0-9]_)*

Each alias definition is of the form

Alias_Type NAME = item1, item2, ...

where Alias_Type is one of CWUser_Alias, CWRunas_Alias, CWHost_Alias, or CWCmnd_Alias. A CWNAME is a string of uppercase letters, numbers, and underscore characters ('_'). A CWNAME 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 ::= '!'* username | '!'* '%'group | '!'* '+'netgroup | '!'* User_Alias

A CWUser_List is made up of one or more usernames, system groups (prefixed with '%'), netgroups (prefixed with '+') and other aliases. Each list item may be prefixed with one or more '!' operators. An odd number of '!' operators negate the value of the item; an even number just cancel each other out.

Runas_List ::= Runas_User | Runas_User ',' Runas_List

Runas_User ::= '!'* username | '!'* '#'uid | '!'* '%'group | '!'* +netgroup | '!'* Runas_Alias

A CWRunas_List is similar to a CWUser_List except that it can also contain uids (prefixed with '#') and instead of CWUser_Aliases it can contain CWRunas_Aliases. Note that usernames 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 usernames 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 ::= '!'* hostname | '!'* ip_addr | '!'* network(/netmask)? | '!'* '+'netgroup | '!'* Host_Alias

A CWHost_List is made up of one or more hostnames, \s-1IP\s0 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 with a network number, the netmask of the host's ethernet interface(s) will be used when matching. The netmask may be specified either in dotted quad notation (e.g. 255.255.255.0) or \s-1CIDR\s0 notation (number of bits, e.g. 24). A hostname may include shell-style wildcards (see the Wildcards section below), but unless the CWhostname command on your machine returns the fully qualified hostname, you'll need to use the fqdn option for wildcards to be useful.

Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List

commandname ::= filename | filename args | filename '""'

Cmnd ::= '!'* commandname | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias

A CWCmnd_List is a list of one or more commandnames, directories, and other aliases. A commandname is a fully qualified filename which may include shell-style wildcards (see the Wildcards section below). A simple filename 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 CW"" to indicate that the command may only be run without command line arguments. A directory is a fully qualified pathname ending in a '/'. When you specify a directory in a CWCmnd_List, the user will be able to run any file within that directory (but not in any subdirectories therein).

If a CWCmnd has associated command line arguments, then the arguments in the CWCmnd 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 CW"sudoedit" is used to permit a user to run sudo with the -e flag (or as sudoedit). It may take command line arguments just as a normal command does.

Certain configuration options may be changed from their default values at runtime via one or more CWDefault_Entry lines. These may affect all users on any host, all users on a specific host, a specific user, or commands being run as a specific user.

Default_Type ::= 'Defaults' | 'Defaults' '@' Host | 'Defaults' ':' User | 'Defaults' '>' RunasUser

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 (CW") when they contain multiple words. Special characters may be escaped with a backslash (CW\).

Lists have two additional assignment operators, CW+= and CW-=. These operators are used to add to and delete from a list respectively. It is not an error to use the CW-= operator to remove an element that does not exist in a list.

"long_otp_prompt" When validating with a One Time Password scheme (S/Key or \s-1OPIE\s0), 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.

"ignore_dot" If set, sudo will ignore '.' or '' (current dir) in the CWPATH environment variable; the CWPATH itself is not modified. This flag is off by default. Currently, while it is possible to set ignore_dot in sudoers, its value is not used. This option should be considered read-only (it will be fixed in a future version of sudo).

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

"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.

"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.

"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.

"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. This flag is off by default.

"tty_tickets" If set, users must authenticate on a per-tty basis. Normally, sudo uses a directory in the ticket dir with the same name as the user running it. With this flag enabled, sudo will use a file named for the tty the user is logged in on in that directory. This flag is off by default.

"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 CWPASSWD and CWNOPASSWD tags. This flag is on by default.

"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 CW"sudo sudo /bin/sh". Note, however, that turning off root_sudo will also prevent root and from running sudoedit. Disabling root_sudo provides no real additional security; it exists purely for historical reasons. This flag is on by default.

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

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

"shell_noargs" If set and sudo is invoked with no arguments it acts as if the -s flag had been given. That is, it runs a shell as root (the shell is determined by the CWSHELL 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.

"set_home" If set and sudo is invoked with the -s flag the CWHOME 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 flag imply -H. This flag is off by default.

"always_set_home" If set, sudo will set the CWHOME 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 flag is always implied. This flag is off by default.

"path_info" Normally, sudo will tell the user when a command could not be found in their CWPATH 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 CWPATH, sudo will tell the user that they are not allowed to run it, which can be confusing. This flag is off by default.

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

"fqdn" Set this flag if you want to put fully qualified hostnames 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 \s-1DNS\s0 lookups which may make affect sudo performance if \s-1DNS\s0 stops working (for example if the machine is not plugged into the network). The default behavior for Debian has been modified to minimize the potential of a problem, but there may still be some cases in which lack of working \s-1DNS\s0 might make sudo work very slowly. Also note that you must use the host's official name as \s-1DNS\s0 knows it. That is, you may not use a host alias (CWCNAME entry) due to performance issues and the fact that there is no way to get all aliases from \s-1DNS\s0. If your machine's hostname (as returned by the CWhostname command) is already fully qualified you shouldn't need to set fqdn. This flag is on by default.

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

"requiretty" If set, sudo will only run when the user is logged in to a real tty. This will disallow things like CW"rsh somehost sudo ls" since rsh(1) does not allocate a tty. Because it is not possible to turn off echo when there is no tty present, some sites may with to set this flag to prevent a user from entering a visible password. This flag is off by default.

"env_editor" If set, visudo will use the value of the \s-1EDITOR\s0 or \s-1VISUAL\s0 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 CWeditor variable. visudo will then only use the \s-1EDITOR\s0 or \s-1VISUAL\s0 if they match a value specified in CWeditor. This flag is CWon by default.

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

"runaspw" If set, sudo will prompt for the password of the user defined by the runas_default option (defaults to CWroot) instead of the password of the invoking user. This flag is off by default.

"targetpw" If set, sudo will prompt for the password of the user specified by the -u flag (defaults to CWroot) instead of the password of the invoking user. Note that this precludes the use of a uid not listed in the passwd database as an argument to the -u flag. This flag is off by default.

"set_logname" Normally, sudo will set the CWLOGNAME and CWUSER environment variables to the name of the target user (usually root unless the -u flag is given). However, since some programs (including the \s-1RCS\s0 revision control system) use CWLOGNAME 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.

"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 \s-1UID\s0 is left as the invoking user's \s-1UID\s0. 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. Note, however, that this means that sudo will run with the real uid of the invoking user which may allow that user to kill sudo before it can log a failure, depending on how your \s-1OS\s0 defines the interaction between signals and setuid processes.

"env_reset" If set, sudo will reset the environment to only contain the following variables: CWHOME, CWLOGNAME, CWPATH, CWSHELL, CWTERM, CWDISPLAY, CWXAUTHORITY, CWXAUTHORIZATION, CWLANG, CWLANGUAGE, CWLC_*, and CWUSER (in addition to the CWSUDO_* variables). Of these, only CWTERM, CWDISPLAY, CWXAUTHORITY, CWXAUTHORIZATION, CWLANG, CWLANGUAGE, and CWLC_* are copied unaltered from the old environment. The other variables are set to default values (possibly modified by the value of the set_logname option). If sudo was compiled with the CWSECURE_PATH option, its value will be used for the CWPATH environment variable. This option is enabled by default. Other variables may be preserved with the env_keep option.

"use_loginclass" 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.

"noexec" If set, all commands run via sudo will behave as if the CWNOEXEC tag has been set, unless overridden by a CWEXEC tag. See the description of \s-1NOEXEC\s0 and \s-1EXEC\s0 below as well as the “\s-1PREVENTING\s0 \s-1SHELL\s0 \s-1ESCAPES\s0” section at the end of this manual. This flag is off by default.

"ignore_local_sudoers" If set via \s-1LDAP\s0, parsing of CW@sysconfdir@/sudoers will be skipped. This is intended for an Enterprises that wish to prevent the usage of local sudoers files so that only \s-1LDAP\s0 is used. This thwarts the efforts of rogue operators who would attempt to add roles to CW@sysconfdir@/sudoers. When this option is present, CW@sysconfdir@/sudoers does not even need to exist. Since this options tells sudo how to behave when no specific \s-1LDAP\s0 entries have been matched, this sudoOption is only meaningful for the cn=defaults section. This flag is off by default.

"passwd_tries" The number of tries a user gets to enter his/her password before sudo logs the failure and exits. The default is CW3.

"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 default is CW80 (use 0 or negate the option to disable word wrap).

"timestamp_timeout" Number of minutes that can elapse before sudo will ask for a passwd again. The default is CW15. Set this to CW0 to always prompt for a password. If set to a value less than CW0 the user's timestamp will never expire. This can be used to allow users to create or delete their own timestamps via CWsudo -v and CWsudo -k respectively.

"passwd_timeout" Number of minutes before the sudo password prompt times out. The default is CW0, set this to CW0 for no password timeout.

"umask" Umask to use when running the command. Negate this option or set it to 0777 to preserve the user's umask. The default is CW0022.

"mailsub" Subject of the mail sent to the mailto user. The escape CW%h will expand to the hostname of the machine. Default is CW*** SECURITY information for %h ***.

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

"timestampdir" The directory in which sudo stores its timestamp files. The default is /var/run/sudo.

"timestampowner" The owner of the timestamp directory and the timestamps stored therein. The default is CWroot.

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

"runas_default" The default user to run commands as if the -u flag is not specified on the command line. This defaults to CWroot. Note that if runas_default is set it must occur before any CWRunas_Alias specifications.

"syslog_goodpri" Syslog priority to use when user authenticates successfully. Defaults to CWnotice.

"syslog_badpri" Syslog priority to use when user authenticates unsuccessfully. Defaults to CWalert.

"editor" A colon (':') separated list of editors allowed to be used with visudo. visudo will choose the editor that matches the user's \s-1USER\s0 environment variable if possible, or the first editor in the list that exists and is executable. The default is the path to vi on your system.

"noexec_file" 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 CWLD_PRELOAD or its equivalent. Defaults to /usr/lib/sudo/sudo_noexec.so.

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

"never" Never lecture the user.

"once" Only lecture the user the first time they run sudo.

"always" Always lecture the user.

"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.

"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.

"syslog" Syslog facility if syslog is being used for logging (negate to disable syslog logging). Defaults to CWauthpriv.

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

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

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

"exempt_group" Users in this group are exempt from password and \s-1PATH\s0 requirements. This option is turned on for Debian.

"verifypw" This option controls when a password will be required when a user runs sudo with the -v flag. It has the following possible values:

"all" All the user's sudoers entries for the current host must have the CWNOPASSWD flag set to avoid entering a password.

"any" At least one of the user's sudoers entries for the current host must have the CWNOPASSWD flag set to avoid entering a password.

"never" The user need never enter a password to use the -v flag.

"always" The user must always enter a password to use the -v flag.

"listpw" This option controls when a password will be required when a user runs sudo with the -l flag. It has the following possible values:

"all" All the user's sudoers entries for the current host must have the CWNOPASSWD flag set to avoid entering a password.

"any" At least one of the user's sudoers entries for the current host must have the CWNOPASSWD flag set to avoid entering a password.

"never" The user need never enter a password to use the -l flag.

"always" The user must always enter a password to use the -l flag.

"env_check" Like env_keep, but listed environment variables are taken from the user's environment if the variable's value does not contain CW% or CW/ 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 CW=, CW+=, CW-=, and CW! operators respectively. The default list of environment variables to check is printed when sudo is run by root with the -V option.

"env_delete" Not effective due to security issues: only variables listed in env_keep or env_check can be passed through sudo! 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 CW=, CW+=, CW-=, and CW! operators respectively. The default list of environment variables to remove is printed 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" Environment variables to be preserved in the user's environment. 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 CW=, CW+=, CW-=, and CW! operators respectively. This list has no default members.

When logging via syslog(3), sudo accepts the following values for the syslog facility (the value of the syslog Parameter): authpriv (if your \s-1OS\s0 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.

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? Tag_Spec* Cmnd

Runas_Spec ::= '(' Runas_List ')'

Tag_Spec ::= ('NOPASSWD:' | 'PASSWD:' | 'NOEXEC:' | 'EXEC:')

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.

Let's break that down into its constituent parts:

A CWRunas_Spec is simply a CWRunas_List (as defined above) enclosed in a set of parentheses. If you do not specify a CWRunas_Spec in the user specification, a default CWRunas_Spec of root will be used. A CWRunas_Spec sets the default for 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 CWRunas_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.

A command may have zero or more tags associated with it. There are four possible tag values, CWNOPASSWD, CWPASSWD, CWNOEXEC, CWEXEC. Once a tag is set on a CWCmnd, subsequent CWCmnds in the CWCmnd_Spec_List, inherit the tag unless it is overridden by the opposite tag (ie: CWPASSWD overrides CWNOPASSWD and CWEXEC overrides CWNOEXEC).

By default, sudo requires that a user authenticate him or herself before running a command. This behavior can be modified via the CWNOPASSWD tag. Like a CWRunas_Spec, the CWNOPASSWD tag sets a default for the commands that follow it in the CWCmnd_Spec_List. Conversely, the CWPASSWD 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 as root 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 CWPASSWD tag has no effect on users who are in the group specified by the exempt_group option.

By default, if the CWNOPASSWD tag is applied to any of the entries for a user on the current host, he or she will be able to run CWsudo -l without a password. Additionally, a user may only run CWsudo -v without a password if the CWNOPASSWD 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.

If sudo has been compiled with noexec support and the underlying operating system support it, the CWNOEXEC 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 “\s-1PREVENTING\s0 \s-1SHELL\s0 \s-1ESCAPES\s0” section below for more details on how noexec works and whether or not it will work on your system.

sudo allows shell-style wildcards (aka meta or glob characters) to be used in pathnames as well as command line arguments in the sudoers file. Wildcard matching is done via the \s-1POSIX\s0 fnmatch(3) routine. Note that these are not regular expressions. Matches any set of zero or more characters. Matches any single character. Matches any character in the specified range. Matches any character not in the specified range. For any character “x”, evaluates to “x”. This is used to escape special characters such as: “*”, “?”, “[”, and “}”.

Note that a forward slash ('/') will not be matched by wildcards used in the pathname. When matching the command line arguments, however, a slash does get matched by wildcards. This is to make a path like:

/usr/bin/*

match /usr/bin/who but not /usr/bin/X11/xterm.

\s-1WARNING:\s0 a pathname with wildcards will not match a user command that consists of a relative path. In other words, given the following sudoers entry:

billy workstation = /usr/bin/*

user billy will be able to run any command in /usr/bin as root, such as /usr/bin/w. The following two command will be allowed (the first assumes that /usr/bin is in the user's path):

$ sudo w $ sudo /usr/bin/w

However, this will not:

$ cd /usr/bin $ sudo ./w

For this reason you should only grant access to commands using wildcards and never restrict access using them. This limitation will be removed in a future version of sudo.

The following exceptions apply to the above rules: If the empty string CW"" is the only command line argument in the sudoers entry it means that command is not allowed to be run with any arguments.

The pound sign ('#') is used to indicate a comment (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 \s-1ALL\s0 is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a CWCmnd_Alias, CWUser_Alias, CWRunas_Alias, or CWHost_Alias. You should not try to define your own alias called \s-1ALL\s0 as the built-in alias will be used in preference to your own. Please note that using \s-1ALL\s0 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 CWCmnd. This allows one to exclude certain values. Note, however, that using a CW! in conjunction with the built-in CWALL alias to allow a user to run “all but a few” commands rarely works as intended (see \s-1SECURITY\s0 \s-1NOTES\s0 below).

Long lines can be continued with a backslash ('\') as the last character on the line.

Whitespace 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 username or hostname): '@', '!', '=', ':', ',', '(', ')', '\'.

/etc/sudoers List of who can run what /etc/group Local groups file /etc/netgroup List of network groups

Since the sudoers file is parsed in a single pass, order is important. In general, you should structure sudoers such that the CWHost_Alias, CWUser_Alias, and CWCmnd_Alias specifications come first, followed by any CWDefault_Entry lines, and finally the CWRunas_Alias and user specifications. The basic rule of thumb is you cannot reference an Alias that has not already been defined.

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 .Xauthority file # Note that some programs may use HOME for other purposes too 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

# 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

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 CWLOGNAME or CWUSER environment variables when running commands as root. Additionally, on the machines in the \s-1SERVERS\s0 CWHost_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.

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

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 CWNOPASSWD tag).

jack CSNETS = ALL

The user jack may run any command on the machines in the \s-1CSNETS\s0 alias (the networks CW128.138.243.0, CW128.138.204.0, and CW128.138.242.0). Of those networks, only CW128.138.204.0 has an explicit netmask (in \s-1CIDR\s0 notation) indicating it is a class C network. For the other networks in \s-1CSNETS\s0, 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 \s-1CUNETS\s0 alias (the class B network CW128.138.0.0).

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-z]*, !/usr/bin/passwd root

The user pete is allowed to change anyone's password except for root on the \s-1HPPA\s0 machines. Note that this assumes passwd(1) does not take multiple usernames on the command line.

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

The user bob may run anything on the \s-1SPARC\s0 and \s-1SGI\s0 machines as any user listed in the \s-1OP\s0 CWRunas_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 \s-1DB\s0 CWRunas_Alias (oracle or sybase) without giving a password.

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

On the \s-1ALPHA\s0 machines, user john may su to anyone except root but he is not allowed to give su(1) any flags.

jen ALL, !SERVERS = ALL

The user jen may run any command on any machine except for those in the \s-1SERVERS\s0 CWHost_Alias (master, mail, www and ns).

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

For any machine in the \s-1SERVERS\s0 CWHost_Alias, jill may run any commands in the directory /usr/bin/ except for those commands belonging to the \s-1SU\s0 and \s-1SHELLS\s0 CWCmnd_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 \s-1WEBMASTERS\s0 CWUser_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 \s-1CDROM\s0 CWHost_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.

It is generally not effective to “subtract” commands from CWALL 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 \s-1SU\s0 or \s-1SHELLS\s0 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).

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 restrictions. Common programs that permit shell escapes include shells (obviously), editors, paginators, mail and terminal programs.

Many systems that support shared libraries have the ability to override default library functions by pointing an environment variable (usually CWLD_PRELOAD) 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.

To tell whether or not sudo supports noexec, you can run the following as root:

sudo -V | grep "dummy exec"

If the resulting output contains a line that begins with:

File containing dummy exec functions:

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, \s-1IRIX\s0, Tru64 \s-1UNIX\s0, MacOS X, and HP-UX 11.x. It is known not to work on \s-1AIX\s0 and UnixWare. Noexec is expected to work on most operating systems that support the CWLD_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 CWLD_PRELOAD is supported.

To enable noexec for a command, use the CWNOEXEC 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 see if it works.

Note that disabling 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.

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 hostnames in the netgroup (as is usually the case), you either need to have the machine's hostname be fully qualified as returned by the CWhostname 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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