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August 20, 2016


restricted user shell


rush.rc - configuration rules for rush.


The file /etc/rush.rc contains a set of rules that the rush(1) shell uses in order to determine whether the user is allowed to execute the requested command and to set up the environment for its execution.
Empty lines are ignored. Lines beginning with a pound sign are comments and are ignored as well.
A statement consists of a keyword and optional argument, separated by any amount of whitespace. Depending on the keyword, the statement may treat its argument as a single value or as multiple values.
If the keyword requires multiple values, its argument is split into words using the following algorithm:
0step]. Any sequence of one or more non-whitespace characters is a word.
0[step]. Any sequence of characters enclosed in single or double quotes is a word.
0[step]. Words are separated by any amount of white space.
0[step]. If the keyword expects s-expressions these are treated as words, even if they contain white space.
Arguments obtained as a result of rules (1) and (2) are subject to backslash interpretation, during which the following escape sequences are replaced with single characters:
        Sequence    Replaced with
        \a          Audible bell character (ASCII 7)
        \b          Backspace character (ASCII 8)
        \e          Escape character (ASCII 27)
        \f          Form-feed character (ASCII 12)
        \n          Newline character (ASCII 10)
        \r          Carriage return character (ASCII 13)
        \t          Horizontal tabulation character (ASCII 9)
        \v          Vertical tabulation character (ASCII 11)
        \\          A single backslash
        \\(dq       A double-quote.
Any escape sequence not listed in this table is replaced with its second character.
Statements are delimited by newline characters. Length of a statement line is not limited. To improve readability, long statements may be split over several lines by using backslash as a last character on line.


include FILE
Include the content of the named FILE.
If FILE starts with ~/, these two characters are replaced with the full path name of current user home directory.
If FILE is a directory, that directory is searched for a file whose name coincides with the current user name. If such a file is found, it is included.
In any case, if the named file does not exist, no error is reported, and parsing of the configuration file continues.
include-security ARG...
Configures the security checks that a file must pass in order to be included in the configuration by the include statement. The arguments are a whitespace-separated list of check names. The following check names are available:
all Enable all checks.
owner The file must be owned by root.
iwgrp, groupwritablefile
Reject group-writable files.
iwoth, worldwritablefile
Reject world-writable files.
dir_iwgrp, groupwritabledir
Reject files that reside in a group writable directory.
dir_iwoth, worldwritabledir
Reject files that reside in a world writable directory.
link The file may not be is a symbolic link to a file residing in a group or world writable directory.
debug NUMBER
Sets the debugging level. The greater is the NUMBER, the more verbose is the logging. The debugging information is reported via syslog(3) using authpriv, priority debug.
Currently, three debugging levels are implemented:
1 A minimum debugging level, and the only one whose messages are logged using the priority notice. At this level, rush only logs requests and rules selected to handle them.
2 List all actions executed when serving requests.
3 Verbosely describe parsing of the configuration file.
regex FLAGS
Defines what kind of regular expressions will be used in subsequent command, match, and transform statements.
Each flag is a word specifying some regular expression feature. It can be preceded by + to enable this feature (this is the default), or by - to disable it. Valid flags are:
Use POSIX Extended Regular Expression syntax. This is the default.
basic Use basic regular expressions. Equivalent to -extended.
icase Do not differentiate case. Subsequent regex matches will be case insensitive.
usage-error TEXT
Define a textual message which is returned to the remote party if a usage error occurs. The default is
You are not permitted to execute this command.
nologin-error TEXT
Define a textual message which is returned to the remote user if there is no such user name in the password database. The default is:
You do not have interactive login access to this machine.
config-error TEXT
Define a textual message which is returned to the remote party if a system error occurs. The default is:
A system error occurred while attempting to execute command.


Statements are grouped into rules. A rule begins with the following construct
rule TAG
The TAG argument is optional. If it is given, it supplies a a (presumably unique) identifier, which will be used to label this rule. Every diagnostic regarding this rule will be marked with this tag. For rules without explicit tag, default tags will be supplied, constructed by concatenating a pound character and the ordinal number of rule in the configuration file, in decimal notation (rule numbering starts from 1).
The statements that can be used within a rule fall into several distinct categories.


A conditional statement evaluates to a boolean value. All conditionals are tested in order of their appearance in the rule and are tied together using boolean shortcut AND evaluation: if any of them yields false, the rest of statements is skipped and next rule is tried.
command REGEX
True, if the current command line matches regular expression REGEX. By default, POSIX extended regular expressions are used. This, however can be changed using the regex (see below).
match[N] \IREGEX
True, if the Nth word from the command line matches regular expression REGEX. Notice, that square brackets form part of the statement syntax. A special symbol $ can be used instead of N to denote the last word.
The command line is split into words using the same rules as used in /bin/sh.
argc OP NUM
Compare the number of command line arguments to NUM. The comparison operator OP can be one of the following: = (or ==), !=, <, <=, >, >=.
uid [OP] UID
Compare the UID of the user who started rush to UID. The latter may be either a numeric UID or a name of an existing user. The comparison operator OP has the same values as discussed above. If absent, == is assumed.
gid [OP] GID
Compare the GID of the user who started rush to GID. It can be either a numeric value or a name of an existing group. The comparison operator OP has the same values as discussed above. If absent, == is assumed.
user NAMES
Argument is a whitespace-separated list of user names. This condition yields true, if the user name matches one of the listed names. String comparisons are case-sensitive.
group NAMES
Argument is a whitespace-separated list of group names. This condition yields true, if the the name of any group the user is a member of matches one of listed names. String comparisons are case-sensitive.


These statements transform the command line.
Replaces entire command line with the expansion of PATTERN.
Replaces the Nth word in the command line with the expansion of PATTERN. Notice, that square brackets are part of the statement syntax.
Deletes the Nth word.
delete N M
Deletes words between N and M, inclusive.
transform EXPR
Apply a sed(1) expression EXPR to entire command line. For example, the statement below adds a -t option after the command name:
transform s/^[^[:space:]]+/& -t/
transform PATTERN EXPR
Applies the sed(1) expression EXPR to the expansion of PATTERN and replaces entire command line with the result.
transform[N] EXPR
Applies expression EXPR to the Nth word from the command line. Notice, that square brackets are part of the statement syntax.
transform[N] PATTERN EXPR
Applies the expression EXPR to the expansion of PATTERN and replaces N word in the command line with the result.
E.g. to replace the 0th argument with the base name of the command prefixed with a dash:
transform[0] ${^} s,.*/,-,
VN DFL Expand the PATTERN and scan the disk file FILE for the record whose KNth word matches the expansion (words are delimited with characters from DELIM). If found, replace the Nth command line word with the VNth word from the record.
The arguments are:
N Index of the word in command line.
FILE Name of the map file. It must be an absolute file name (i.e. it must start with / or ~/fR.
DELIM A string containing allowed field delimiters.
The value of the lookup key. Before using, it is expanded as described above.
KN Number of the key field in FILE. Fields are numbered starting from 1.
VN Number of the value field.
DFL If supplied, this value is used as a replacement value, when the key was not found in @var{file}.
The map file consists of records, separated by newline characters. Each record consists of fields, separated by delimiters given the DELIM argument. If DELIM contains a space character, then fields may be delimited by any amount of whitespace characters (spaces and/or tabulations). Otherwise, exactly one delimiter delimits fields.
Fields are numbered starting from 1.

System Actions

System actions provide interface to the operating system.
umask MASK
Set the umask. The argument is an octal value not greater than 0777. The default umask is 022.
newgrp GID
Changes the current group ID to GID, which is either a numeric value or a name of an existing group. The keyword can also be spelled as newgroup.
chroot DIR
Change the root directory to DIR. This directory will be used for file names beginning with /. A tilde at the start of DIR is replaced with the user’s home directory.
chdir DIR
Change to the directory DIR. The argument is subject to tilde-expansion as in chroot, above. If both chdir and chroot are specified, then chroot is executed first.
limits RES
Imposes limits on system resources. The argument consists of commands, optionally separated by any amount of whitespace. A command is a single command letter followed by a number, that specifies the limit. The command letters are case-insensitive and coincide with those used by the shell ulimit utility.
        Command     The limit it sets
        A           max address space (KB)
        C           max core file size (KB)
        D           max data size (KB)
        F           maximum file size (KB)
        M           max locked-in-memory address space (KB)
        N           max number of open files
        R           max resident set size (KB)
        S           max stack size (KB)
        T           max CPU time (MIN)
        U           max number of processes
        L           max number of logins for this user (see below)
        P           process priority -20..20
If some limit cannot be set, execution of the rule aborts.
The use of the L resource automatically enables forked mode.


env ARG...
Modifies the execution environment. Arguments are a list of specifiers separated by any amount of whitespace. Each specifier can contain references to variables from the inherited environment. The reference syntax is the same as in sh(1).
The following specifiers are allowed:
- (a dash)
Clear the environment. If used, this must be the very first argument.
-NAME Unset the environment variable NAME.
Unset the environment variable NAME only if its value is VAL.
NAME Retain the environment variable NAME.
Set the environment variable NAME to the given VALUE.
Retain the variable NAME and append VALUE to its value. If no such variable is present in the environment, it is created and VALUE is assigned to it. However, if VALUE starts with a punctuation character, this character is removed from it before the assignment. This is convenient for using this construct with environment variables like PATH, e.g.:
Retain variable VALUE and add VALUE to the beginning of its value. If no such variable is defined in the environment, it is created and VALUE is assigned to it. However, if VALUE ends with a punctuation character, this character is removed from it before assignment.


Declares a fall-through rule -- a special rule that does not execute the requested command. Instead, when rush encounters a matching fall-through rule, it evaluates it and continues scanning its configuration for the next matching rule. Any transformations and environment modifications found in the fall-through rule take effect immediately, which means that subsequent rules will see modified command line and environment. Execution of any other actions found in the fall-through rule is delayed until a usual rule is found.
rule default
umask 002

Interactive Access

Marks the rule it appears in as interactive.
When rush is invoked without -c option (interactive usage), it will consider only rules marked with interactive keywords. This allows for providing interactive shell access.
The default interactive rule terminates by invoking /bin/sh.
The command name argument (argv[0]) is set to the basename of the program being executed prefixed with a dash.
rule login
group shell
set[0] /bin/bash

Accounting and Forked Mode

GNU Rush is able to operate in two modes, called default and forked. When operating in the default mode, the process image of rush itself is overwritten by the command being executed. Thus, when it comes to launching the requested command, the running instance of rush ceases to exist.
In forked mode, rush executes the requested command in a subprocess, and remains in memory supervising its execution. Once the command terminates, the main rush process exits too.
fork BOOL
Enable or disable forked mode. The values yes, on, t, true, 1 stand for true, and no, off, nil, false, or 0 stand for false.
The main advantage of the forked mode is that it allows one to run accounting, i.e., to note who is doing what and to keep a history of invocations. The accounting, in turn, can be used to limit simultaneous executions of commands, as requested by the L command in the limit statement (see above).
acct BOOL
Turn accounting mode on or off, depending on BOOL.
Notice, that there is no need in explicit acct on command, if you use the limit statement with L command, as this enables accounting implicitly.
Most often, accounting should affect all rules and therefore it is normally used in a fall-through rule at the beginning of the configuration file, e.g.:
rule default
acct on


post-socket URL
After completing the command, notify the socket at URL about the fact. This statement implies forked mode.
Valid formats for URL are:
Connect to remote HOST using TCP/IP. HOST is the host name or IP address of the remote machine. Optional PORTspecifies the port number to connect to. It can be either a decimal port number or a service name from /etc/services. If absent, TCPMUX (port 1) is assumed.
unix://FILENAME, or local://FILENAME
Connect to a UNIX socket.
The GNU Rush notification protocol is based on TCPMUX.
After establishing connection, rush sends the rule tag followed by a CRLF pair. The rule tag acts as a service name. The remote party replies with a plus or minus character, indicating positive or negative acknowledgment, immediately followed by an optional message of explanation, and terminated with a CRLF.
If positive acknowledgment is received, rush sends a single line, consisting of the user name and the executed command line, separated by a single space character. The line is terminated with a CRLF.
After sending this line, rush closes the connection.


Write textual message to a file descriptor, given by the optional argument FD. If FD is absent, the descriptor 2 (standard error) is used.
The MESSAGE argument is subject to backslash interpretation.


The following configuration directives control localization.
locale NAME
Sets the locale name.
locale-dir DIR
Sets the name of the locale directory.
text-domain NAME
Sets the textual domain name.


Sergey Poznyakoff


Report bugs to <>.


Copyright © 2016 Sergey Poznyakoff
License GPLv3+: GNU GPL version 3 or later <>
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.


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