rstartd Man page

RSTARTD(1) General Commands Manual RSTARTD(1)


rstartd – a sample implementation of a Remote Start rsh helper



rstartd.real [-c configfilename]


Rstartd is an implementation of a Remote Start “helper” as defined in
“A Flexible Remote Execution Protocol Based on rsh”.

This document describes the peculiarities of rstartd and how it is con‐


-c configfilename
This option specifies the “global” configuration file that
rstartd is to read. Normally, rstartd is a shell script that
invokes rstartd.real with the -c switch, allowing local config‐
uration of the location of the configuration file. If
rstartd.real is started without the -c option, it reads

It is critical to successful interoperation of the Remote Start proto‐
col that rstartd be installed in a directory which is in the “default”
search path, so that default rsh requests and the ilk will be able to
find it.

Rstartd is by design highly configurable. One would like things like
configuration file locations to be fixed, so that users and administra‐
tors can find them without searching, but reality is that no two ven‐
dors will agree on where things should go, and nobody thinks the origi‐
nal location is “right”. Thus, rstartd allows one to relocate all of
its files and directories.

Rstartd has a hierarchy of configuration files which are executed in
order when a request is made. They are:
global config
per-user (“local”) config
global per-context config
per-user (“local”) per-context config
config from request
As you might guess from the presence of “config from request”, all of
the config files are in the format of an rstart request. Rstartd
defines a few additional keywords with the INTERNAL- prefix for speci‐
fying its configuration.

Rstartd starts by reading and executing the global config file. This
file will normally specify the locations of the other configuration
files and any systemwide defaults.

Rstartd will then read the user’s local config file, default name

Rstartd will then start interpreting the request.

Presumably one of the first lines in the request will be a CONTEXT
line. The context name is converted to lower case.

Rstartd will read the global config file for that context, default name
/usr/lib/X11/rstart/contexts/, if any.

It will then read the user’s config file for that context, default name
$HOME/.rstart.contexts/, if any.

(If neither of these exists, rstartd aborts with a Failure message.)

Rstartd will finish interpreting the request, and execute the program

This allows the system administrator and the user a large degree of
control over the operation of rstartd. The administrator has final
say, because the global config file doesn’t need to specify a per-user
config file. If it does, however, the user can override anything from
the global file, and can even completely replace the global context
config files.

The config files have a somewhat more flexible format than requests do;
they are allowed to contain blank lines and lines beginning with “#”
are comments and ignored. (#s in the middle of lines are data, not
comment markers.)

Any commands run are provided a few useful pieces of information in
environment variables. The exact names are configurable, but the sup‐
plied defaults are:

$RSTART_GLOBAL_CONTEXTS the global contexts directory
$RSTART_LOCAL_CONTEXTS the local contexts directory
$RSTART_GLOBAL_COMMANDS the global generic commands directory
$RSTART_LOCAL_COMMANDS the local generic commands directory

$RSTART_{GLOBAL,LOCAL}_CONTEXTS should contain one special file, @List,
which contains a list of the contexts in that directory in the format
specified for ListContexts. The supplied version of ListContexts will
cat both the global and local copies of @List.

Generic commands are searched for in several places: (defaults)
per-user per-context directory ($HOME/.rstart.commands/)
global per-context directory (/usr/lib/X11/rstart/commands/)
per-user all-contexts directory ($HOME/.rstart.commands)
global all-contexts directory (/usr/lib/X11/rstart/commands)
(Yes, this means you can’t have an all-contexts generic command with
the same name as a context. It didn’t seem like a big deal.)

Each of these directories should have a file called @List that gives
the names and descriptions of the commands in that directory in the
format specified for ListGenericCommands.

There are several “special” rstart keywords defined for rstartd config‐
uration. Unless otherwise specified, there are no defaults; related
features are disabled in this case.

Gives a space-separated list of “MISC” registries that this
system understands. (Registries other than this are accepted
but generate a Warning.)

INTERNAL-LOCAL-DEFAULT relative_filename
Gives the name ($HOME relative) of the per-user config file.

INTERNAL-GLOBAL-CONTEXTS absolute_directory_name
Gives the name of the system-wide contexts directory.

INTERNAL-LOCAL-CONTEXTS relative_directory_name
Gives the name ($HOME relative) of the per-user contexts direc‐

INTERNAL-GLOBAL-COMMANDS absolute_directory_name
Gives the name of the system-wide generic commands directory.

INTERNAL-LOCAL-COMMANDS relative_directory_name
Gives the name ($HOME relative) of the per-user generic com‐
mands directory.

Gives the prefix for the configuration environment variables
rstartd passes to its kids.

INTERNAL-AUTH-PROGRAM authscheme program argv[0] argv[1] …
Specifies the program to run to set up authentication for the
specified authentication scheme. “program argv[0] …” gives
the program to run and its arguments, in the same form as the
EXEC keyword.

Specifies the data to be given to the authorization program as
its standard input. Each argument is passed as a single line.
$n, where n is a number, is replaced by the n’th argument to
the “AUTH authscheme arg1 arg2 …” line.

INTERNAL-PRINT arbitrary text
Prints its arguments as a Debug message. Mostly for rstartd
debugging, but could be used to debug config files.

When using the C shell, or any other shell which runs a script every
time the shell is started, the script may get run several times. In
the worst case, the script may get run three times:
By rsh, to run rstartd
By rstartd, to run the specified command
By the command, eg xterm
rstartd currently limits lines, both from config files and requests, to
BUFSIZ bytes.

DETACH is implemented by redirecting file descriptors 0,1, and 2 to
/dev/null and forking before executing the program.

CMD is implemented by invoking $SHELL (default /bin/sh) with “-c” and
the specified command as arguments.

POSIX-UMASK is implemented in the obvious way.

The authorization programs are run in the same context as the target
program – same environment variables, path, etc. Long term this might
be a problem.

In the X context, GENERIC-CMD Terminal runs xterm. In the OpenWindows
context, GENERIC-CMD Terminal runs cmdtool.

In the X context, GENERIC-CMD LoadMonitor runs xload. In the OpenWin‐
dows context, GENERIC-CMD LoadMonitor runs perfmeter.

GENERIC-CMD ListContexts lists the contents of @List in both the sys‐
tem-wide and per-user contexts directories. It is available in all

GENERIC-CMD ListGenericCommands lists the contents of @List in the sys‐
tem-wide and per-user commands directories, including the per-context
subdirectories for the current context. It is available in all con‐

CONTEXT None is not implemented.

CONTEXT Default is really dull.

For installation ease, the “contexts” directory in the distribution
contains a file “@Aliases” which lists a context name and aliases for
that context. This file is used to make symlinks in the contexts and
commands directories.

All MISC values are passed unmodified as environment variables.

One can mistreat rstartd in any number of ways, resulting in anything
from stupid behavior to core dumps. Other than by explicitly running
programs I don’t think it can write or delete any files, but there’s no
guarantee of that. The important thing is that (a) it probably won’t
do anything REALLY stupid and (b) it runs with the user’s permissions,
so it can’t do anything catastrophic.

@List files need not be complete; contexts or commands which are dull
or which need not or should not be advertised need not be listed. In
particular, per-user @List files should not list things which are in
the system-wide @List files. In the future, perhaps ListContexts and
ListGenericCommands will automatically suppress lines from the system-
wide files when there are per-user replacements for those lines.

Error handling is OK to weak. In particular, no attempt is made to
properly report errors on the exec itself. (Perversely, exec errors
could be reliably reported when detaching, but not when passing the
stdin/out socket to the app.)

If compiled with -DODT1_DISPLAY_HACK, rstartd will work around a bug in
SCO ODT version 1. (1.1?) (The bug is that the X clients are all com‐
piled with a bad library that doesn’t know how to look host names up
using DNS. The fix is to look up a host name in $DISPLAY and substi‐
tute an IP address.) This is a trivial example of an incompatibility
that rstart can hide.


rstart, rsh, A Flexible Remote Execution Protocol Based on rsh


Jordan Brown, Quarterdeck Office Systems

X Version 11 rstart 1.0.5 RSTARTD(1)

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