GNU Queue is a UNIX process network
load-balancing system that features an innovative proxy process
mechanism which allows users to control their remote jobs in a nearly
seamless and transparent fashion. When an interactive remote job is
launched, such as say Matlab, or EMACS interfacing Allegro Lisp, a
proxy process runs on the local end. (You can think of this being
equivalent to a running `telnet' or `rsh' process, but more intelligent.)
By sending signals to the local
proxy - including hitting the suspend key - the process on the remote
end may be controlled. Resuming the proxy process resumes the remote job. The
user's environment is almost completely replicated, including not only
environmental variables, but nice values, rlimits, terminal settings
are all replicated on the remote end. Together with MIT_MAGIC_COOKIE_1
(or xhost +) the system is X-windows transparent as well,
provided the users local DISPLAY variable is set to the fully
qualified pathname of the local machine.
One of the most appealing features of the proxy process system even with experienced users is that asynchronous job control of remote jobs by the shell is possible and intuitive. One simply runs the stub in the background under the local shell; the shell notifies the user when the remote job has a change in status by monitoring the stub daemon.
When the remote process has terminated, the proxy process returns the exit value to the shell; otherwise, the stub simulates a death by the same signal as that which terminated or suspended the remote job. In this way, control of the remote process is intuitive even to novice users, as it is just like controlling a local job from the shell. Many of my original users had to be reminded that their jobs were, in fact, running remotely.
In addition, Queue also features a more traditional distributed batch
processing environment, with results returned to the user via
email. In addition, traditional batch processing limitations may be
placed on jobs running in either environment (stub or with the email
mechanism) such as suspension of jobs if the system exceeds a certain
load average, limits on CPU time, disk free requirements, limits on
the times in which jobs may run, etc. (These are documented in the
sample profile file included.)
Queue may be installed by any user on the system; root privileges are not required.
Installing GNU Queue as an ordinary user is recommended only if you lack root (aka, superuser or Unix system administrative privileges) on your cluster.
You do not need to have system administrative privileges to install GNU Queue.
However, To allow all users in the cluster to use GNU Queue you should have your cluster's system administrator install Queue following the instructions in the chapter Install By Root. See section Installation of GNU Queue by System Administrator (Preferred). However, if this is impractical, you may install Queue yourself without resorting to administrative superuser, or root, privileges by following the instructions in this chapter.
Note that, under its default configuration, GNU Queue supports only one installation per cluster, so if you install GNU Queue as an ordinary user you will be the only user able to run jobs through it. This can be overcome if another user edits GNU Queue's header files to change its network port numbers to avoid a conflict with another copy of GNU Queue running on the same cluster.
See section Installation by Ordinary User, on -DHAVE_IDENTD and
running an RFC 931 identd service on cluster when installating GNU Queue as an ordinary user.
To do this, you will need write access to an NFS directory that is shared among all hosts in your cluster. In most cases, your system administrator will have set up your home directory this way.
Installing GNU Queue for one user:
./configure .
When installing as an ordinary user, configure sets the makefile to install GNU Queue into the
current directory. queue will go in ./bin, queued daemon will go into ./sbin, /com/queue
will be the shared spool directory, the host access control list file will go into
./share and the queued pid files will go into ./var . If you want things to go somewhere else,
run ./configure --prefix=dir, where dir is the top-level directory where you want things to be installed.
./configure takes a number of additional options that you may wish to be aware of, ./configure --help gives
a full listing of them. --bindir specifies where queue goes, --sbindir specifies where queued goes,
--sharedstatedir where the spool directory goes, --datadir where the host access control file goes,
and --localstatefile where the queued pid files go.
If ./configure fails inelegantly, make sure lex is installed. GNU flex
is an implementation of lex available from the FSF, http://www.gnu.org.
make to compile the programs.
make install will install the programs into directory you specified with ./configure. Missing
directories will be created.
The name of the localhost make install is being run on will be added to the host access control list if it is not
already there.
make install on the localhost the localhost should already
be in the host access control list file.)
./queue --help gives a list of options to Queue.
Here are some simple examples:
> queue -i -w -n -- hostname > queue -i -r -n -- hostnameHere is a more sophisticated example. Try suspending and resuming it with Control-Z and 'fg':
> queue -i -w -p -- emacs -nwIf this example works on the localhost, you want want to add additional hosts to the host access control list in
share (or --datadir) and start up queued on these.
> queue -i -w -p -h hostname -- emacs -nwwill run emacs on
hostname. Without the -h argument, it will run the job on the
best or least-loaded host in the ACL. See section Configure a Job Queue's profile File, for details on how
host selection is made.
You can also create additional queues for use with the -q and -d commands,
as outlined for root users below. Each spooldir must have a profile file
associated with it. See section Configure a Job Queue's profile File, for details.
If you want to just experiment with Queue on a single host, all you
need is a local directory that is protected to be root-accessible only.
For load-balancing, however,
you will need an NFS directory mounted on all your hosts with
'no_root_squash' (see NFS man pages) option turned on. Unfortunately,
the 'no_root_squash' option is required for load-balancing
because the file system is
used to communicate information about jobs to be run. The default
spool directory is under the default GNU sharedstatedir, /usr/local/com/queue.
no_root_squash option is the GNU/Linux name. The option is named differently under different platforms, see your NFS man pages for the name of the option that prevents root mapping to nobody on client requests.
Installing GNU Queue for cluster-wide usage
./configure option is to install GNU Queue in the local directory for use by
a single user only.
System administrators need to specify --enable-root to reconfigure GNU to run with root
privileges. This turns off some options, for example, privileged ports are used instead of
relying on the identd (RFC 931) service if it is installed. See section Security Issues,
for a discussion of security issues
Run ./configure --enable-root .
When installing with the --enable-root option, configure sets the Makefile to install GNU Queue under
the /usr/local prefix. queue will go in /usr/local/bin, queued daemon will go into /usr/local/sbin,
/usr/local/com/queue will be the shared spool directory, the host access control list file will go into
/usr/local/share and the queued pid files will go into /usr/local/var . If you want things to go somewhere else,
run ./configure --enable-root --prefix=dir, where dir is the top-level directory where you want things to be installed.
./configure --enable-root takes a number of additional options that you may wish to be aware of, ./configure --help gives
a full listing of them. --bindir specifies where queue goes, --sbindir specifies where queued goes,
--sharedstatedir where the spool directory goes, --datadir where the host access control file goes,
and --localstatefile where the queued pid files go.
If ./configure fails inelegantly, make sure lex is installed. GNU Flex
is an implementation of lex available from the FSF, http://www.gnu.org.
make to compile the programs.
make install will install the programs into directory you specified with ./configure. Missing
directories will be created.
The name of the localhost make install is being run on will be added to the host access control list if it is not
already there.
make install on the localhost the localhost should already
be in the host access control list file.)
./queue --help gives a list of options to Queue.
Here are some simple examples:
> queue -i -w -n -- hostname > queue -i -r -n -- hostnameHere is a more sophisticated example. Try suspending and resuming it with Control-Z and 'fg':
> queue -i -w -p -- emacs -nwIf this example works on the localhost, you want want to add additional hosts to the host access control list in
share (or --datadir) and start up queued on these.
> queue -i -w -p -h hostname -- emacs -nwwill run emacs on
hostname. Without the -h argument, it will run the job on the
"best" or "least-loaded" host in the ACL. See Profile for details on how
host selection is made. See section Configure a Job Queue's profile File.
You can also create additional queues for use with the -q and -d commands,
as outlined for users below. Each spooldir must have a profile file
associated with it. See section Configure a Job Queue's profile File, for details.
The GNU Queue system consists of two components, `queued' which runs as a daemon on every host in the cluster, and `queue' is a user program that allows users to submit jobs to the system.
The 'queue' binary contacts queued to learn the relative virtual load averages (explained in 'profile') on each host, and specifies one on which to run the job. Queued then forks off a process and works together with queue on the local end to control the remote job.
Look over the sample 'profile' file, See section Configure a Job Queue's profile File, to learn how to customize batch queues and load balancing. 'profile' has many options. Among others, you can configure certain hosts to be submit-only hosts for all or only certain job classes by turning off job execution in these queues.
Add the name of each host in the cluster to the access control list. The default
location for this is either share/qhostsfile or /usr/local/share/qhostsfile
depending on how ./configure was invoked.
Finally, if you are installing GNU Queue cluster-wide,
make sure the spool directory (default is /usr/local/com/queue)
is NFS exported root-writable on all systems in
your cluster. In GNU/Linux, this is done by setting the
no_root_squash option in /etc/exports (and then running /usr/etc/exportfs
to cause the system to acknowlege the changes; if /usr/etc/exportfs is
not available on your system, restart nfsd and the portmapper.)
Other operating system flavors have different names for this option. Read nfs(4),
exports(4) and other man pages for information on setting the
no_root_squash equivalent on your operating system flavor.
queue
queue [-h hostname|-H hostname] [-i|-q] [-d spooldir]
[-o|-p|-n] [-w|-r] -- command.options
qsh [-l ignored] [-d spooldir] [-o|-p|-n]
[-w|-r] hostname command command.options
now spooldir) and queue (queue spooldir).
-q option, specifies the name of the batch processing directory, e.g., matlab
The defaults for qsh are a slightly different: no-pty emulation is the default, and a hostname argument is
required. A plus (+) is the wildcard hostname; specifying + in place of a valid hostname is the
same as not using an -h or -H option with queue. qsh is envisioned
as a rsh compatibility mode for use with software that expects a rsh-like syntax.
This is useful with some MPI implementations; See section Running GNU Queue with MPI and PVM..
Start the Queue system on every system in
your cluster (as you defined in queue.h) by running queued or
queued -D & from the directory in which queued is
installed.
The later invocation places queued in debug
mode, with copious error messages and mailings, which is probably a
good idea if you are having problems. Sending queued a kill -HUP will
force it to re-read the profile files and ACL lists, which is good when you wish to
shut down a queue or add hosts to the cluster. queued will also periodically
check for modifications to these files.
If all has gone well at this stage, you may now try submitting a
sample job to the system. I recommend trying something like queue -i
-w -p -- emacs -nw. You should be able to background and foreground the
remote EMACS process from the local shell just as if it were running
as a local copy.
Another example command is queue -i -w -- hostname which should
return the best host (i.e., least loaded, as controlled by options in
the profile file; See section Configure a Job Queue's profile File, to run a job on.
The options on queue need to be explained:
-i specifies immediate execution mode, placing the job in the now
spool. This is the default. Alternatively, you may specify either the -q option,
which is shorthand for the wait spool, or use the -d
spooldir option to place the job under the control of the profile file
in the spooldir subdirectory of the spool directory, which must previously
have been created by the Queue administrator.
In any case, execution of the job will wait until it satisfies the conditions of the profile file for that particular spool directory, which may include waiting for a slot to become free. This method of batch processing is completely compatible with the stub mechanism, although it may disorient users to use it in this way as they may be unknowingly forced to wait until a slot on a remote machine becomes available.
-w activates the stub mechanism, which is the default.
The queue stub process will
terminate when the remote process terminates; you may send signals and
suspend/resume the remote process by doing the same to the stub
process. Standard input/output will be that of the 'queue' stub
process. -r deactivates the stub process; standard input/output will
be via email back to the users; the queue process will return
immediately.
-p or -n specifies whether or not a virtual tty should be
allocated at the remote end, or whether the system should merely use
the more efficient socket mechanism. Many interactive processes, such
as EMACS or Matlab, require a virtual tty to be present, so the -p
option is required for these. Other processes, such as a simple
hostname do not require a tty and so may be run without the
default -p. Note that queue is intelligent and will override
the -p option if it detects both stdio/stdout have been re-directed
to a non-terminal; this feature is useful in facilitating system
administration scripts that allow users to execute jobs. [At some
point we may wish to change the default to -p as the system
automatically detects when -n will suffice.] Simple, non-interactive
jobs such as hostname do not need the less efficient pty/tty
mechanism and so should be run with the -n option. The -n option
is the default when queue is invoked in rsh compatibility mode
with qsh.
The -- with queue specifies `end of queue options' and everything beyond this
point is interpreted as the command, or arguments to be given to the
command. Consequently, user options (i.e., when invoking queue through
a script front end, may be placed here):
#!/bin/sh exec queue -i -w -p -- sas $*
or
#!/bin/sh exec queue -q -w -p -d sas -- sas $*
for example. This places queue in immediate mode following
instructions in the now spool subdirectory (first example) or in
batch-processing mode into the sas spool subdirectory, provided it
has been created by the administrator. In both cases, stubs are being
used, which will not terminate until the sas process terminates on the
remote end.
In both cases, pty/ttys will be allocated, unless the user redirects
both the standard input and standard output of the simple invoking
scripts. Invoking queue through these scripts has the additional
advantage that the process name will be that of the script, clarifying
what is the process is. For example, the script might called sas or
sas.remote, causing queue to appear this way in the user's process
list.
queue can be used for batch processing by using the -q -r -n
options, e.g.,
#!/bin/sh exec queue -q -r -n -d sas -- sas $*
would run SAS in batch mode. -q and -d sas options force Queue to
follow instructions in the sas/profile file under Queue's spool
directory and wait for the next available job slot. -r activates
batch-processing mode, causing Queue to exit immediately and return
results (including stdout and stderr output) via email.
The final option, -n, is the option to disable allocation of a pty on the
remote end; it is unnecessary in this case (as batch mode disables
ptys anyway) but is here to demonstrate how it might be used in a
-i -w -n or -q -w -n invocation.
Under /usr/spool/queue you may create several directories
for batch jobs, each identified with the class of the
batch job (e.g., sas or splus). You may then place
restrictions on that class, such as maximum number of
jobs running, or total CPU time, by placing a profile
file like this one in that directory.
However, the now queue is mandatory; it is the
directory used by the -i mode (immediate moe)
of queue to launch jobs over the network
immediately rather than as batch jobs.
Specify that this queue is turned on:
exec on
The next two lines in profile may be set to an email address
rather than a file; the leading / identifies
then as file logs. Files now beginning with cf,of, or ef are ignored
by the queued:
mail /usr/local/com/queue/now/mail_log supervisor /usr/local/com/queue/now/mail_log2
Note that /usr/local/com/queue is our spool directory, and now is
the job batch directory for the special now queue (run via the -i
or immediate-mode flag to the queue executable), so these files
may reside in the job batch directories.
The pfactor command is used to control the likelihood
of a job being executed on a given machine. Typically, this is done
in conjunction with the host command, which specifies that the option
on the rest of the line be honored on that host only.
In this example, pfactor is set to the relative MIPS of each
machine, for example:
host fast_host pfactor 100 host slow_host pfactor 50
Where fast_host and slow_host are the hostnames of the respective machines.
This is useful for controlling load balancing. Each queue on each machine reports back an `apparant load average' calculated as follows:
1-min load average/ (( max(0, vmaxexec - maxexec) + 1)*pfactor)
The machine with the lowest apparant load average for that queue is the one most likely to get the job.
Consequently, a more powerful pfactor proportionally reduces the load average
that is reported back for this queue, indicating a more
powerful system.
Vmaxexec is the "apparant maximum" number of jobs allowed to execute in this queue, or simply equal to maxexec if it was not set. The default value of these variables is large value treated by the system as infinity.
host fast_host vmaxexec 2 host slow_host vmaxexec 1 maxexec 3
The purpose of vmaxexec is to make the system appear fully loaded
at some point before the maximum number of jobs are already
running, so that the likelihood of the machine being used
tapers off sharply after vmaxexec slots are filled.
Below vmaxexec jobs, the system aggressively discriminates against
hosts already running jobs in this Queue.
In job queues running above vmaxexec jobs, hosts appear more equal to the system,
and only the load average and pfactor is used to assign jobs. The theory here is that above vmaxexec jobs, the hosts are fully saturated, and the load average is a better indicator than the simple number of jobs running in a job queue of where
to send the next job.
Thus, under lightly-loaded situations, the system routes jobs around hosts
already running jobs in this job queue. In more heavily loaded situations,
load-averages and pfactors are used in determining where to run jobs.
Additional options in profile
exec
minfree
maxfree
loadsched
loadstop
timesched
timestop
nice
rlimitcpu
rlimitdata
rlimitstack
rlimitfsize
rlimitrss
rlimitcore
These options, if present, will only override the
user's values (via queue) for these limits if they are lower
than what the user has set (or larger in the case of nice).
Many MPI implementations (such as the free MPICH implementation) allow you to specify a replacment utility for rsh/remsh to propagate processes.
Just use qsh as the replacement. Be sure the QHOSTSFILE lists all hosts
known to the MPI implementation, and the queued is running on them.
You have three options: place a + in the MPI hosts file for each job-slot
you want MPI to be able to start, explicitly list Queue's hosts in the
MPI host file, or use a combination of + wild-cards and explicitly listed
hosts in MPI's host file.
The + is GNU Queue's wild-card character for the hostname when it is invoked
using qsh. It simply means that Queue should decide what host the process should
run on, which is the default behavior for Queue. Specifying a host instead of
using the + with qsh is equivalent to the -h option with the regular queue
command-line syntax.
By placing +s in the MPI host file, MPI will pass + as the name of the
host for that job slot to GNU Queue, which, in turn, will decide where the job
should actually run.
By running jobs through GNU Queue this way, GNU Queue becomes aware of jobs
submitted by MPI, and can route non-MPI jobs around them. Normally, you would
want to use a job queue (-j option) which has a low vmaxexec set and a high
maxexec, so that MPI's jobs will continue to run, but GNU Queue will
aggressively try to route jobs to other hosts the moment the job queue
begins the fill.
GNU Queue's load scheduling algorithm is smarter than that of many MPI
implementations, which frequently treat all hosts as equal and implement
a round-robin algorithm for deciding which to host to run a job on. GNU
Queue, on the other hand, can take load-averages, CPU power differences (via
profile file specifiers), and other factors into account when deciding
on which host to send a particular job to.
qsh represent a stage-1 hook for MPI. Our development team (See section Getting Help,
for information on joining the development team) is currently working on a stage-2 hook,
in which MPI becomes aware of GNU Queue jobs as well, allowing them to work as an
integrated scheduling team.
Support for PVM is currently in development as well.
Security is always a concern when granting root privileges to software.
I was security conscious and knowledgeable about UNIX security issues when I wrote queue. It should be paranoid in all the right places, at least provided that the spool directory is root-accessible only (standard installation) or user-accessible (installation by ordinary user) only.
Critical ports allow connections only by hosts in the access control list.
Standard checks (TCP/IP wrapper-style) are made to prevent DNS spoofing
and IP forwarding as much as possible. In addition, connections must
be made from privileged ports (root installation version). queue.c and queued.c
run with least-privileges, revoking root privileges as soon as they have
verified information and acquired a privileged port.
Moreover, at the time of this writing the source code has been available for a number of months and has been used at numerous installations, including some concerned with security.
However, this does not guarantee that security holes do no exist.
It is important that security-conscious users scrutinize the source code and
report any potential security problems to bug-queue@gnu.org. By promptly
reporting security issues you will be supporting free software by
ensuring that the public availability of source code is a security
asset.
In this installation mode, GNU Queue takes many of the same precautions for these users as when it has been installed cluster-wide by a system administrator.
Unfortunately, when Queue is installed by an ordinary user, privileged
ports are not available. This might make it possible for a malicious user already having a shell
account on the same cluster to have queued or queue try to spoof each other.
To close this hole, Queue uses the one-way function crypt(3) and a cookie passed over NFS to allow queued and
queue to authenticate each other. These cookies are used in the root version
as well to prevent port confusion by queued trying to connect to a queue
that has earlier died, although they aren't useful from a security standpoint.
When GNU Queue is compiled with the -DHAVE_IDENTD
(and -DNO_ROOT),
queued and queue also use the identd service (RFC 931)
to prevent spoofing by checking the ownership of remote sockets
within the cluster. For this to work proplery, identd must be running on all your cluster hosts, return accurate information (either the
user's login name as given in the password file or his/her uid), and at
least accept connections from within the cluster in a reasonable amount of
time. The ./configure script
tries to set -DHAVE_IDENTD automatically based on whether or not your host accepts local
connections to port 113, but some systems intentionally allow identd to output
bogus information for privacy reasons, and -DHAVE_IDENTD
should not be set on these; if this is the case, you may need to re-compile GNU Queue with
HAVE_IDENTD undefined in config.h. Fortunately,
queue will normally complain immediately if -DHAVE_IDENTD
is set when it shouldn't be.
To get around the performance hit of calling the crypt(3), one-way
functions are not used if spoofing queued is impossible due to
privilege ports (root installation) or
authenticated ports (HAVE_IDENTD service), so running identd
with GNU Queue or installing GNU Queue cluster-wide as root may offer
a slight performance advantange. In sites which normally send user
passwords over the network in cleartext it is not expected to substancial
improve secure over the cookie passing mechanism, however.
These cookies are passed in plaintext, which means that a malicious user
might be able to observe the NFS network traffic between the hosts and, having shell access on the cluster, might still be able to spoof queue or
queued. Since most sites send UNIX account passwords
over the network in cleartext as well, this is only of concern
in very secure sites that do not pass passwords in cleartext over the network.
In the rare event that your site is a very secure site that does not send
passwords in cleartext, and you are compiling Queue without root privileges,
you should have your administrator install the identd (RFC 931)
service and re-run ./configure to ensure HAVE_IDENTD is defined
in config.h.
If your very secure site prefers to spoof identd for privacy reasons,
your administrator may be able to restrict identd access
with tcp_wrapper or install an accurate identd on a
non-standard port which could restrict connections to within the cluster
via tcp_wrapper. You would need to re-compile GNU Queue with this
new port number set in ident.c. Another option is to have your
system administrator install Queue cluster-wide; this uses privileged ports
and therefore may operate securely with resorting to identd.
These concerns do not apply when Queue has been installed cluster-wide by
root (NO_ROOT is not defined),
because privileged ports are then available.
PLEASE SEND US FEEDBACK ON QUEUE!
Whether you have a queue-tip, are queue-less about how to solve a
problem, or simply have another bad queue joke, que[ue] us in at
bug-queue@gnu.org and we'll take our que[ue] from you on how best
to improve the software and documentation.
The application's homepage is
http://queue.sourceforge.net.
Bug reports should be sent to the bug list bug-queue@gnu.org.
Users are encouraged to subscribe to and request assistance from the development list, `queue-developers', as well.
At the time of this writing, the list was working on several fun projects, including improved MPI & PVM support, secure socket connections, AFS & Kerberos support. We're also porting and improving a nifty utility that lets you monitor and control the execution of Queue jobs throughout your cluster. The list is a great way to tap into the group's expertise and keep up with the latest developments.
So, come join the fun and keep up with the latest developments by visiting
http://lists.sourceforge.net/mailman/listinfo/queue-developers.
It is also possible to subscribe from the application's homepage.
It is http://queue.sourceforge.net.
At the time of this writing, GNU Queue is being maintained by GNU Queue's primary author, Werner G. Krebs.
Copyright (C) 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.
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To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.
one line to give the program's name and an idea of what it does. Copyright (C) 19yy name of author This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Also add information on how to contact you by electronic and paper mail.
If the program is interactive, make it output a short notice like this when it starts in an interactive mode:
Gnomovision version 69, Copyright (C) 19yy name of author Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than `show w' and `show c'; they could even be mouse-clicks or menu items--whatever suits your program.
You should also get your employer (if you work as a programmer) or your school, if any, to sign a "copyright disclaimer" for the program, if necessary. Here is a sample; alter the names:
Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. signature of Ty Coon, 1 April 1989 Ty Coon, President of Vice
This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.
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