SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) NNAAMMEE sudoers - list of which users may execute what DDEESSCCRRIIPPTTIIOONN The _s_u_d_o_e_r_s 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 _s_u_d_o_e_r_s 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. QQuuiicckk gguuiiddee ttoo EEBBNNFF EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of _p_r_o_d_u_c_­ _t_i_o_n _r_u_l_e_s. E.g., symbol ::= definition | alternate1 | alternate2 ... Each _p_r_o_d_u_c_t_i_o_n _r_u_l_e references others and thus makes up a grammar for the language. EBNF also contains the follow­ ing operators, which many readers will recognize from reg­ ular expressions. Do not, however, confuse them with "wildcard" characters, which have different meanings. ? Means that the preceding symbol (or group of sym­ bols) is optional. That is, it may appear once or not at all. * Means that the preceding symbol (or group of sym­ bols) may appear zero or more times. + Means that the preceding symbol (or group of sym­ bols) 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). AAlliiaasseess There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias. 1.6.8p5 November 28, 2004 1 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) 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 _a_l_i_a_s definition is of the form Alias_Type NAME = item1, item2, ... where _A_l_i_a_s___T_y_p_e is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias. A NAME is a string of upper­ case letters, numbers, and underscore characters ('_'). A NAME mmuusstt 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 _a_l_i_a_s member follow. User_List ::= User | User ',' User_List User ::= '!'* username | '!'* '%'group | '!'* '+'netgroup | '!'* User_Alias A User_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 1.6.8p5 November 28, 2004 2 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) A Runas_List is similar to a User_List except that it can also contain uids (prefixed with '#') and instead of User_Aliases it can contain Runas_Aliases. Note that usernames and groups are matched as strings. In other words, two users (groups) with the same uid (gid) are con­ sidered 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 ::= '!'* hostname | '!'* ip_addr | '!'* network(/netmask)? | '!'* '+'netgroup | '!'* Host_Alias A Host_List is made up of one or more hostnames, 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 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 CIDR notation (number of bits, e.g. 24). A hostname may include shell-style wildcards (see the Wildcards section below), but unless the hostname command on your machine returns the fully qualified host­ name, you'll need to use the _f_q_d_n option for wildcards to be useful. Cmnd_List ::= Cmnd | Cmnd ',' Cmnd_List commandname ::= filename | filename args | filename '""' Cmnd ::= '!'* commandname | '!'* directory | '!'* "sudoedit" | '!'* Cmnd_Alias A Cmnd_List is a list of one or more commandnames, direc­ tories, and other aliases. A commandname is a fully qual­ ified 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 "" to indicate that the command may only be run wwiitthhoouutt command line arguments. A directory is a fully qualified pathname ending in a '/'. When you specify a 1.6.8p5 November 28, 2004 3 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) directory in a Cmnd_List, the user will be able to run any file within that directory (but not in any subdirectories 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 argu­ ments: ',', ':', '=', '\'. The special command "sudoedit" is used to permit a user to run ssuuddoo with the --ee flag (or as ssuuddooeeddiitt). It may take command line arguments just as a normal command does. DDeeffaauullttss Certain configuration options may be changed from their default values at runtime via one or more Default_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 ffllaaggss, iinntteeggeerr values, ssttrriinnggss, or lliissttss. 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 dis­ able 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. FFllaaggss: long_otp_prompt When validating with a One Time Password 1.6.8p5 November 28, 2004 4 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) scheme (SS//KKeeyy or OOPPIIEE), 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 _o_f_f by default. ignore_dot If set, ssuuddoo will ignore '.' or '' (current dir) in the PATH environment variable; the PATH itself is not modified. This flag is _o_f_f by default. Currently, while it is possible to set _i_g_n_o_r_e___d_o_t in _s_u_d_o_e_r_s, its value is not used. This option should be considered read- only (it will be fixed in a future version of ssuuddoo). mail_always Send mail to the _m_a_i_l_t_o user every time a users runs ssuuddoo. This flag is _o_f_f by default. mail_badpass Send mail to the _m_a_i_l_t_o user if the user run­ ning sudo does not enter the correct password. This flag is _o_f_f by default. mail_no_user If set, mail will be sent to the _m_a_i_l_t_o user if the invoking user is not in the _s_u_d_o_e_r_s file. This flag is _o_n by default. mail_no_host If set, mail will be sent to the _m_a_i_l_t_o user if the invoking user exists in the _s_u_d_o_e_r_s file, but is not allowed to run commands on the current host. This flag is _o_f_f by default. mail_no_perms If set, mail will be sent to the _m_a_i_l_t_o user if the invoking user is allowed to use ssuuddoo but the command they are trying is not listed in their _s_u_d_o_e_r_s file entry or is explicitly denied. This flag is _o_f_f by default. tty_tickets If set, users must authenticate on a per-tty basis. Normally, ssuuddoo uses a directory in the ticket dir with the same name as the user run­ ning it. With this flag enabled, ssuuddoo will use a file named for the tty the user is logged in on in that directory. This flag is _o_f_f by default. authenticate If set, users must authenticate themselves via a password (or other means of authentication) before they may run commands. This default 1.6.8p5 November 28, 2004 5 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) may be overridden via the PASSWD and NOPASSWD tags. This flag is _o_n by default. root_sudo If set, root is allowed to run ssuuddoo too. Dis­ abling this prevents users from "chaining" ssuuddoo commands to get a root shell by doing something like "sudo sudo /bin/sh". Note, however, that turning off _r_o_o_t___s_u_d_o will also prevent root and from running ssuuddooeeddiitt. Dis­ abling _r_o_o_t___s_u_d_o provides no real additional security; it exists purely for historical rea­ sons. This flag is _o_n by default. log_host If set, the hostname will be logged in the (non-syslog) ssuuddoo log file. This flag is _o_f_f by default. log_year If set, the four-digit year will be logged in the (non-syslog) ssuuddoo log file. This flag is _o_f_f by default. shell_noargs If set and ssuuddoo is invoked with no arguments it acts as if the --ss flag had been given. That is, it runs a shell as root (the shell is determined by the SHELL 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 _o_f_f by default. set_home If set and ssuuddoo is invoked with the --ss flag the HOME environment variable will be set to the home directory of the target user (which is root unless the --uu option is used). This effectively makes the --ss flag imply --HH. This flag is _o_f_f by default. always_set_home If set, ssuuddoo will set the HOME environment variable to the home directory of the target user (which is root unless the --uu option is used). This effectively means that the --HH flag is always implied. This flag is _o_f_f by default. path_info Normally, ssuuddoo will tell the user when a com­ mand could not be found in their PATH environ­ ment 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 disadvan­ tage is that if the executable is simply not in the user's PATH, ssuuddoo will tell the user that they are not allowed to run it, which can 1.6.8p5 November 28, 2004 6 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) be confusing. This flag is _o_f_f by default. preserve_groups By default ssuuddoo will initialize the group vec­ tor to the list of groups the target user is in. When _p_r_e_s_e_r_v_e___g_r_o_u_p_s 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 _o_f_f by default. fqdn Set this flag if you want to put fully quali­ fied hostnames in the _s_u_d_o_e_r_s file. I.e., instead of myhost you would use myhost.mydo­ main.edu. You may still use the short form if you wish (and even mix the two). Beware that turning on _f_q_d_n requires ssuuddoo to make DNS lookups which may make ssuuddoo 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 (CNAME entry) due to performance issues and the fact that there is no way to get all aliases from DNS. If your machine's hostname (as returned by the hostname command) is already fully qualified you shouldn't need to set _f_q_d_n. This flag is _o_f_f by default. insults If set, ssuuddoo will insult users when they enter an incorrect password. This flag is _o_f_f by default. requiretty If set, ssuuddoo will only run when the user is logged in to a real tty. This will disallow things like "rsh somehost sudo ls" since _r_s_h(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 _o_f_f by default. env_editor If set, vviissuuddoo will use the value of the EDI­ TOR 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 editor variable. vviissuuddoo will then only use the EDITOR or VISUAL if they match a value specified in editor. This flag is off by default. 1.6.8p5 November 28, 2004 7 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) rootpw If set, ssuuddoo will prompt for the root password instead of the password of the invoking user. This flag is _o_f_f by default. runaspw If set, ssuuddoo will prompt for the password of the user defined by the _r_u_n_a_s___d_e_f_a_u_l_t option (defaults to root) instead of the password of the invoking user. This flag is _o_f_f by default. targetpw If set, ssuuddoo will prompt for the password of the user specified by the --uu flag (defaults to root) 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 --uu flag. This flag is _o_f_f by default. set_logname Normally, ssuuddoo will set the LOGNAME and USER environment variables to the name of the tar­ get user (usually root unless the --uu flag is given). However, since some programs (includ­ ing the RCS revision control system) use LOG­ NAME 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 ssuuddoo 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 ssuuddoo 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 ssuuddoo before it can log a failure, depending on how your OS defines the interac­ tion between signals and setuid processes. env_reset If set, ssuuddoo will reset the environment to only contain the following variables: HOME, LOGNAME, PATH, SHELL, TERM, and USER (in addi­ tion to the SUDO_* variables). Of these, only TERM is copied unaltered from the old environ­ ment. The other variables are set to default values (possibly modified by the value of the _s_e_t___l_o_g_n_a_m_e option). If ssuuddoo was compiled with the SECURE_PATH option, its value will be used for the PATH environment variable. Other variables may be preserved with the _e_n_v___k_e_e_p 1.6.8p5 November 28, 2004 8 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) option. use_loginclass If set, ssuuddoo will apply the defaults specified for the target user's login class if one exists. Only available if ssuuddoo is configured with the --with-logincap option. This flag is _o_f_f by default. noexec If set, all commands run via sudo will behave as if the NOEXEC tag has been set, unless overridden by a EXEC tag. See the description of _N_O_E_X_E_C _a_n_d _E_X_E_C below as well as the "PRE­ VENTING SHELL ESCAPES" section at the end of this manual. This flag is _o_f_f by default. ignore_local_sudoers If set via LDAP, parsing of @sysconfdir@/sudo­ ers will be skipped. This is intended for an 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 @sysconfdir@/sudoers. When this option is present, @sysconfdir@/sudoers does not even need to exist. Since this options tells sudo how to behave when no specific LDAP entries have been matched, this sudoOption is only meaningful for the cn=defaults section. This flag is _o_f_f by default. IInntteeggeerrss: passwd_tries The number of tries a user gets to enter his/her password before ssuuddoo logs the failure and exits. The default is 3. IInntteeggeerrss tthhaatt ccaann bbee uusseedd iinn aa bboooolleeaann ccoonntteexxtt: 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 80 (use 0 or negate the option to disable word wrap). timestamp_timeout Number of minutes that can elapse before ssuuddoo will ask for a passwd again. The default is 5. Set this to 0 to always prompt for a pass­ word. If set to a value less than 0 the user's timestamp will never expire. This can be used to allow users to create or delete 1.6.8p5 November 28, 2004 9 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) their own timestamps via sudo -v and sudo -k respectively. passwd_timeout Number of minutes before the ssuuddoo password prompt times out. The default is 5, set this to 0 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 0022. SSttrriinnggss: mailsub Subject of the mail sent to the _m_a_i_l_t_o user. The escape %h will expand to the hostname of the machine. Default is *** SECURITY informa­ tion for %h ***. badpass_message Message that is displayed if a user enters an incorrect password. The default is Sorry, try again. unless insults are enabled. timestampdir The directory in which ssuuddoo stores its times­ tamp files. The default is _/_v_a_r_/_r_u_n_/_s_u_d_o. timestampowner The owner of the timestamp directory and the timestamps stored therein. The default is root. passprompt The default prompt to use when asking for a password; can be overridden via the --pp option or the SUDO_PROMPT environment variable. The following percent (`%') escapes are supported: %u expanded to the invoking user's login name %U expanded to the login name of the user the command will be run as (defaults to root) %h expanded to the local hostname without the domain name %H expanded to the local hostname includ­ ing the domain name (on if the machine's hostname is fully qualified or the _f_q_d_n option is set) %% two consecutive % characters are 1.6.8p5 November 28, 2004 10 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) collaped into a single % character The default value is Password:. runas_default The default user to run commands as if the --uu flag is not specified on the command line. This defaults to root. Note that if _r_u_n_a_s___d_e_f_a_u_l_t is set it mmuusstt occur before any Runas_Alias specifications. syslog_goodpri Syslog priority to use when user authenticates successfully. Defaults to notice. syslog_badpri Syslog priority to use when user authenticates unsuccessfully. Defaults to alert. editor A colon (':') separated list of editors allowed to be used with vviissuuddoo. vviissuuddoo will choose the editor that matches the user's USER environment variable if possible, or the first editor in the list that exists and is exe­ cutable. The default is the path to vi on your system. noexec_file Path to a shared library containing dummy ver­ sions of the _e_x_e_c_v_(_), _e_x_e_c_v_e_(_) and _f_e_x_e_c_v_e_(_) library functions that just return an error. This is used to implement the _n_o_e_x_e_c function­ ality on systems that support LD_PRELOAD or its equivalent. Defaults to _/_u_s_r_/_l_o_c_a_l_/_l_i_b_e_x_e_c_/_s_u_d_o___n_o_e_x_e_c_._s_o. SSttrriinnggss tthhaatt ccaann bbee uusseedd iinn aa bboooolleeaann ccoonntteexxtt: 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 ssuuddoo. always Always lecture the user. If no value is specified, a value of _o_n_c_e is implied. Negating the option results in a value of _n_e_v_e_r being used. The default value is _o_n_c_e. 1.6.8p5 November 28, 2004 11 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) 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 ssuuddoo 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 local2. 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 --tt. mailto Address to send warning and error mail to. The address should be enclosed in double quotes (") to protect against sudo interpret­ ing the @ sign. Defaults to root. exempt_group Users in this group are exempt from password and PATH requirements. This is not set by default. verifypw This option controls when a password will be required when a user runs ssuuddoo with the --vv flag. It has the following possible values: all All the user's _s_u_d_o_e_r_s entries for the current host must have the NOPASSWD flag set to avoid entering a password. any At least one of the user's _s_u_d_o_e_r_s entries for the current host must have the NOPASSWD flag set to avoid enter­ ing a password. never The user need never enter a password to use the --vv flag. always The user must always enter a password to use the --vv flag. If no value is specified, a value of _a_l_l is implied. Negating the option results in a value of _n_e_v_e_r being used. The default value is _a_l_l. 1.6.8p5 November 28, 2004 12 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) listpw This option controls when a password will be required when a user runs ssuuddoo with the --ll flag. It has the following possible values: all All the user's _s_u_d_o_e_r_s entries for the current host must have the NOPASSWD flag set to avoid entering a password. any At least one of the user's _s_u_d_o_e_r_s entries for the current host must have the NOPASSWD flag set to avoid enter­ ing a password. never The user need never enter a password to use the --ll flag. always The user must always enter a password to use the --ll flag. If no value is specified, a value of _a_n_y is implied. Negating the option results in a value of _n_e_v_e_r being used. The default value is _a_n_y. LLiissttss tthhaatt ccaann bbee uusseedd iinn aa bboooolleeaann ccoonntteexxtt: env_check Environment variables to be removed from the user's environment if the variable's value contains % or / characters. This can be used to guard against printf-style format vulnera­ bilities in poorly-written programs. The argument may be a double-quoted, space-sepa­ rated list or a single value without dou­ ble-quotes. The list can be replaced, added to, deleted from, or disabled by using the =, +=, -=, and ! operators respectively. The default list of environment variables to check is printed when ssuuddoo is run by root with the _-_V option. env_delete Environment variables to be removed from the user's environment. The argument may be a double-quoted, space-separated list or a sin­ gle value without double-quotes. The list can be replaced, added to, deleted from, or dis­ abled by using the =, +=, -=, and ! operators respectively. The default list of environment variables to remove is printed when ssuuddoo 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 ssuuddoo). env_keep Environment variables to be preserved in the 1.6.8p5 November 28, 2004 13 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) user's environment when the _e_n_v___r_e_s_e_t option is in effect. This allows fine-grained con­ trol over the environment ssuuddoo-spawned pro­ cesses will receive. The argument may be a double-quoted, space-separated list or a sin­ gle value without double-quotes. The list can be replaced, added to, deleted from, or dis­ abled by using the =, +=, -=, and ! operators respectively. This list has no default mem­ bers. When logging via _s_y_s_l_o_g(3), ssuuddoo accepts the following values for the syslog facility (the value of the ssyysslloogg Parameter): aauutthhpprriivv (if your OS supports it), aauutthh, ddaaee­­ mmoonn, uusseerr, llooccaall00, llooccaall11, llooccaall22, llooccaall33, llooccaall44, llooccaall55, llooccaall66, and llooccaall77. The following syslog priorities are supported: aalleerrtt, ccrriitt, ddeebbuugg, eemmeerrgg, eerrrr, iinnffoo, nnoottiiccee, and wwaarrnniinngg. UUsseerr SSppeecciiffiiccaattiioonn 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 uusseerr ssppeecciiffiiccaattiioonn determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as rroooott, but this can be changed on a per-command basis. Let's break that down into its constituent parts: RRuunnaass__SSppeecc A Runas_Spec is simply a Runas_List (as defined above) enclosed in a set of parentheses. If you do not specify a Runas_Spec in the user specification, a default Runas_Spec of rroooott will be used. A Runas_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 ddggbb may run _/_b_i_n_/_l_s, _/_b_i_n_/_k_i_l_l, and _/_u_s_r_/_b_i_n_/_l_p_r_m -- but only as ooppeerraattoorr. E.g., 1.6.8p5 November 28, 2004 14 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) $ 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 ddggbb is now allowed to run _/_b_i_n_/_l_s as ooppeerraattoorr, but _/_b_i_n_/_k_i_l_l and _/_u_s_r_/_b_i_n_/_l_p_r_m as rroooott. TTaagg__SSppeecc A command may have zero or more tags associated with it. There are four possible tag values, NOPASSWD, PASSWD, NOEXEC, EXEC. 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 (ie: PASSWD overrides NOPASSWD and EXEC overrides NOEXEC). _N_O_P_A_S_S_W_D _a_n_d _P_A_S_S_W_D By default, ssuuddoo 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 rraayy to run _/_b_i_n_/_k_i_l_l, _/_b_i_n_/_l_s, and _/_u_s_r_/_b_i_n_/_l_p_r_m as root on the machine rushmore as rroooott without authenticating himself. If we only want rraayy to be able to run _/_b_i_n_/_k_i_l_l 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 per­ tain to the current host. This behavior may be overridden via the verifypw and listpw options. _N_O_E_X_E_C _a_n_d _E_X_E_C If sudo has been compiled with _n_o_e_x_e_c support and the underlying operating system support it, the NOEXEC tag can be used to prevent a dynamically-linked executable from 1.6.8p5 November 28, 2004 15 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) running further commands itself. In the following example, user aaaarroonn may run _/_u_s_r_/_b_i_n_/_m_o_r_e and _/_u_s_r_/_b_i_n_/_v_i 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 _n_o_e_x_e_c works and whether or not it will work on your system. WWiillddccaarrddss ssuuddoo allows shell-style _w_i_l_d_c_a_r_d_s (aka meta or glob char­ acters) to be used in pathnames as well as command line arguments in the _s_u_d_o_e_r_s file. Wildcard matching is done via the PPOOSSIIXX _f_n_m_a_t_c_h(3) routine. Note that these are _n_o_t regular expressions. * Matches any set of zero or more characters. ? Matches any single character. [...] Matches any character in the specified range. [!...] Matches any character nnoott in the specified range. \x For any character "x", evaluates to "x". This is used to escape special characters such as: "*", "?", "[", and "}". Note that a forward slash ('/') will nnoott be matched by wildcards used in the pathname. When matching the command line arguments, however, a slash ddooeess get matched by wild­ cards. This is to make a path like: /usr/bin/* match _/_u_s_r_/_b_i_n_/_w_h_o but not _/_u_s_r_/_b_i_n_/_X_1_1_/_x_t_e_r_m. WARNING: a pathname with wildcards will nnoott match a user command that consists of a relative path. In other words, given the following _s_u_d_o_e_r_s entry: billy workstation = /usr/bin/* user billy will be able to run any command in /usr/bin as root, such as _/_u_s_r_/_b_i_n_/_w. The following two command will be allowed (the first assumes that _/_u_s_r_/_b_i_n is in the user's path): $ sudo w $ sudo /usr/bin/w 1.6.8p5 November 28, 2004 16 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) However, this will not: $ cd /usr/bin $ sudo ./w For this reason you should only ggrraanntt access to commands using wildcards and never rreessttrriicctt access using them. This limitation will be removed in a future version of ssuuddoo. EExxcceeppttiioonnss ttoo wwiillddccaarrdd rruulleess The following exceptions apply to the above rules: "" If the empty string "" is the only command line argument in the _s_u_d_o_e_r_s entry it means that com­ mand is not allowed to be run with aannyy arguments. OOtthheerr ssppeecciiaall cchhaarraacctteerrss aanndd rreesseerrvveedd wwoorrddss 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 AALLLL is a built-in _a_l_i_a_s 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 _a_l_i_a_s called AALLLL as the built-in alias will be used in preference to your own. Please note that using AALLLL can be dangerous since in a command context, it allows the user to run aannyy command on the system. An exclamation point ('!') can be used as a logical _n_o_t operator both in an _a_l_i_a_s 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. Whitespace between elements in a list as well as special syntactic characters in a _U_s_e_r _S_p_e_c_i_f_i_c_a_t_i_o_n ('=', ':', '(', ')') is optional. The following characters must be escaped with a backslash ('\') when used as part of a word (e.g. a username or hostname): '@', '!', '=', ':', ',', '(', ')', '\'. 1.6.8p5 November 28, 2004 17 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) FFIILLEESS /etc/sudoers List of who can run what /etc/group Local groups file /etc/netgroup List of network groups EEXXAAMMPPLLEESS Since the _s_u_d_o_e_r_s file is parsed in a single pass, order is important. In general, you should structure _s_u_d_o_e_r_s such that the Host_Alias, User_Alias, and Cmnd_Alias spec­ ifications come first, followed by any Default_Entry lines, and finally the Runas_Alias and user specifica­ tions. The basic rule of thumb is you cannot reference an Alias that has not already been defined. Below are example _s_u_d_o_e_r_s entries. Admittedly, some of these are a bit contrived. First, we define our _a_l_i_a_s_e_s: # 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 ssuuddoo to log via _s_y_s_l_o_g(3) using the _a_u_t_h facility in all cases. We don't want to subject the full time staff to the ssuuddoo lecture, user mmiilllleerrtt need not give a password, and we don't want to reset the LOGNAME or USER 1.6.8p5 November 28, 2004 18 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) environment variables when running commands as root. Additionally, on the machines in the _S_E_R_V_E_R_S 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. # 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 _U_s_e_r _s_p_e_c_i_f_i_c_a_t_i_o_n is the part that actually deter­ mines who may run what. root ALL = (ALL) ALL %wheel ALL = (ALL) ALL We let rroooott and any user in group wwhheeeell run any command on any host as any user. FULLTIMERS ALL = NOPASSWD: ALL Full time sysadmins (mmiilllleerrtt, mmiikkeeff, and ddoowwddyy) may run any command on any host without authenticating themselves. PARTTIMERS ALL = ALL Part time sysadmins (bboossttlleeyy, jjwwffooxx, and ccrraawwll) may run any command on any host but they must authenticate them­ selves first (since the entry lacks the NOPASSWD tag). jack CSNETS = ALL The user jjaacckk may run any command on the machines in the _C_S_N_E_T_S 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 _C_S_N_E_T_S, the local machine's netmask will be used during matching. lisa CUNETS = ALL The user lliissaa may run any command on any host in the _C_U_N_E_T_S alias (the class B network 128.138.0.0). operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/ The ooppeerraattoorr user may run commands limited to simple main­ tenance. Here, those are commands related to backups, killing processes, the printing system, shutting down the system, and any commands in the directory _/_u_s_r_/_o_p_e_r_/_b_i_n_/. 1.6.8p5 November 28, 2004 19 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) joe ALL = /usr/bin/su operator The user jjooee may only _s_u(1) to operator. pete HPPA = /usr/bin/passwd [A-z]*, !/usr/bin/passwd root The user ppeettee is allowed to change anyone's password except for root on the _H_P_P_A machines. Note that this assumes _p_a_s_s_w_d(1) does not take multiple usernames on the command line. bob SPARC = (OP) ALL : SGI = (OP) ALL The user bboobb may run anything on the _S_P_A_R_C and _S_G_I machines as any user listed in the _O_P Runas_Alias (rroooott and ooppeerraattoorr). jim +biglab = ALL The user jjiimm may run any command on machines in the _b_i_g_l_a_b netgroup. SSuuddoo knows that "biglab" is a netgroup due to the '+' prefix. +secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser Users in the sseeccrreettaarriieess 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 ffrreedd can run commands as any user in the _D_B Runas_Alias (oorraaccllee or ssyybbaassee) without giving a password. john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root* On the _A_L_P_H_A machines, user jjoohhnn may su to anyone except root but he is not allowed to give _s_u(1) any flags. jen ALL, !SERVERS = ALL The user jjeenn may run any command on any machine except for those in the _S_E_R_V_E_R_S Host_Alias (master, mail, www and ns). jill SERVERS = /usr/bin/, !SU, !SHELLS For any machine in the _S_E_R_V_E_R_S Host_Alias, jjiillll may run any commands in the directory /usr/bin/ except for those commands belonging to the _S_U and _S_H_E_L_L_S Cmnd_Aliases. steve CSNETS = (operator) /usr/local/op_commands/ The user sstteevvee may run any command in the directory 1.6.8p5 November 28, 2004 20 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) /usr/local/op_commands/ but only as user operator. matt valkyrie = KILL On his personal workstation, valkyrie, mmaatttt 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 _W_E_B_M_A_S_T_E_R_S User_Alias (will, wendy, and wim), may run any command as user www (which owns the web pages) or simply _s_u(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. SSEECCUURRIITTYY NNOOTTEESS It is generally not effective to "subtract" commands from ALL using the '!' operator. A user can trivially circum­ vent 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 bbiillll from running the commands listed in _S_U or _S_H_E_L_L_S since he can simply copy those com­ mands 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). PPRREEVVEENNTTIINNGG SSHHEELLLL EESSCCAAPPEESS Once ssuuddoo 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 ssuuddoo'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 abil­ ity to override default library functions by pointing an environment variable (usually LD_PRELOAD) to an alternate shared library. On such systems, ssuuddoo's _n_o_e_x_e_c function­ ality 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 1.6.8p5 November 28, 2004 21 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) running under binary emulation are not affected. To tell whether or not ssuuddoo supports _n_o_e_x_e_c, 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 ssuuddoo may be able to replace the exec family of func­ tions in the standard library with its own that simply return an error. Unfortunately, there is no foolproof way to know whether or not _n_o_e_x_e_c will work at compile-time. _N_o_e_x_e_c should work on SunOS, Solaris, *BSD, Linux, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known nnoott to work on AIX and UnixWare. _N_o_e_x_e_c is expected to work on most operating systems that support the LD_PRELOAD envi­ ronment 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 sup­ ported. To enable _n_o_e_x_e_c for a command, use the NOEXEC tag as doc­ umented in the User Specification section above. Here is that example again: aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi This allows user aaaarroonn to run _/_u_s_r_/_b_i_n_/_m_o_r_e and _/_u_s_r_/_b_i_n_/_v_i with _n_o_e_x_e_c 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 _n_o_e_x_e_c you can always just try it out and see if it works. Note that disabling shell escapes is not a panacea. Pro­ grams running as root are still capable of many poten­ tially hazardous operations (such as changing or overwrit­ ing files) that could lead to unintended privilege escala­ tion. In the specific case of an editor, a safer approach is to give the user permission to run ssuuddooeeddiitt. SSEEEE AALLSSOO _r_s_h(1), _s_u(1), _f_n_m_a_t_c_h(3), sudo(1m), visudo(1m) CCAAVVEEAATTSS The _s_u_d_o_e_r_s file should aallwwaayyss be edited by the vviissuuddoo command which locks the file and does grammatical check­ ing. It is imperative that _s_u_d_o_e_r_s be free of syntax errors since ssuuddoo will not run with a syntactically incor­ rect _s_u_d_o_e_r_s file. 1.6.8p5 November 28, 2004 22 SUDOERS(4) MAINTENANCE COMMANDS SUDOERS(4) 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 hostname command or use the _f_q_d_n option in _s_u_d_o_e_r_s. BBUUGGSS If you feel you have found a bug in ssuuddoo, please submit a bug report at http://www.sudo.ws/sudo/bugs/ SSUUPPPPOORRTT Commercial support is available for ssuuddoo, see http://www.sudo.ws/sudo/support.html for details. Limited free support is available via the sudo-users mail­ ing list, see http://www.sudo.ws/mail­ man/listinfo/sudo-users to subscribe or search the archives. DDIISSCCLLAAIIMMEERR SSuuddoo is provided ``AS IS'' and any express or implied war­ ranties, including, but not limited to, the implied war­ ranties of merchantability and fitness for a particular purpose are disclaimed. See the LICENSE file distributed with ssuuddoo or http://www.sudo.ws/sudo/license.html for com­ plete details. 1.6.8p5 November 28, 2004 23