Contains : aliases (basically variables) and user specifications (which specify who may run what).
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]_)* Alias definitions are of the form: Alias_Type NAME = item1, item2, ...where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or Cmnd_Alias.
NAMEs a string of uppercase letters, numbers, and underscore characters ('_').
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5 The definitions of an alias member: User_List ::= User | User ',' User_List User ::= '!'* username | '!'* '%'group | '!'* '+'netgroup | '!'* User_AliasWhen 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).
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 '!' (negation) operators.
Runas_List ::= Runas_User | Runas_User ',' Runas_List Runas_User ::= '!'* username | '!'* '#'uid | '!'* '%'group | '!'* +netgroup | '!'* Runas_AliasA 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. Usernames and groups are matched as strings. i.e. 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_AliasA Host_List is made up of one or more hostnames, IP addresses, network numbers, netgroups (prefixed with '+') and other aliases. 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 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_AliasA Cmnd_List is a list of 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 and may also specify command line arguments (including wildcards).
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 flag (or as sudoedit). It may take command line arguments just as a normal command does.
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 | '!'* ParameterParameters are flags, integers, strings, or lists and are by default 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 must be enclosed in quotes (") when containing multiple words. Special characters must 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.
|long_otp_prompt|| When validating with a One Time Password scheme (S/Key or OPIE), a two-line prompt is
used. default: off
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: Runas_Spec 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 root 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/lprmThe 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/lprmThen user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root. Tag_Spec 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).
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprmwould 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/lprmNote, 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.
* 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. \x 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. WARNING: 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/wHowever, this will not:
$ cd /usr/bin $ sudo ./wFor 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.
Exceptions to wildcard rules
The following exceptions apply to the above rules: "" If the empty string "" is the only command line argument in the sudoers entry it means that command is not allowed to be run with any arguments.
Other special characters and reserved words
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 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.
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): '@', '!', '=', ':', ',', '(', ')', '\'.
/private/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 Host_Alias, User_Alias, and Cmnd_Alias specifications come first, followed by any Default_Entry lines, and finally the Runas_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 define our aliases:
# 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 = 184.108.40.206/255.255.0.0 Host_Alias CSNETS = 220.127.116.11, 18.104.22.168/24, 22.214.171.124 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/suHere 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 or USER 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.
# 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 NOPASSWD tag). jack CSNETS = ALLThe user jack may run any command on the machines in the CSNETS alias (the networks 126.96.36.199, 188.8.131.52, and 184.108.40.206). Of those networks, only 220.127.116.11 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 18.104.22.168). 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 HPPA 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 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 give su(1) any flags. 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 /CDROMAny 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.
bill ALL = ALL, !SU, !SHELLSDoesn'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).
Many systems that support shared libraries have the ability to override default library functions by pointing an environment variable (usually LD_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, IRIX, Tru64 UNIX, MacOS X, and HP-UX 11.x. It is known not to work on AIX and UnixWare. Noexec is expected to work on most operating systems that support the LD_PRELOAD environment variable. Check your operating sytem'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.
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 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.
from ras[berrypi strech 3/18/18
# This file MUST be edited with the 'visudo' command as root. # # add local content in /etc/sudoers.d/ # # Defaults env_reset Defaults mail_badpass Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin" # User privilege specification root ALL=(ALL:ALL) ALL # Allow members of group sudo to execute any command %sudo ALL=(ALL:ALL) ALL # The following #include is NOT a comment #includedir /etc/sudoers.d # Host alias specification # User alias specification # Cmnd alias specification
SEE ALSO rsh(1), su(1), fnmatch(3), sudo(8), visudo(8)
CAVEATS 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 hostname command or use the fqdn option in sudoers.