NQ(1)

NAME
nq - job queue utility

SYNOPSIS
nq [-c] [-q] command line ...
nq -t job id ...
nq -w job id ...

DESCRIPTION
The nq utility provides a very lightweight queuing system without requiring setup, maintenance, supervision or any long-running processes.

Job order is enforced by a timestamp nq gets immediately when started. Synchronization happens on file-system level. Timer resolution is milliseconds. No sub-second file system time stamps are required. Polling is not used. Exclusive execution is maintained strictly.

You enqueue(!) new jobs into the queue by running

    nq command line ...

The job id (a file name relative to NQDIR, which defaults to the current directory) is output (unless suppressed using -q) and nq detaches from the terminal immediately, running the job in the background. Standard output and standard error are redirected into the job id file. fq(1) can be used to conveniently watch the log files.

The options are as follows:

-c  Clean up job id file when process exited with status 0.

-q  Suppress output of the job id after spawning new job.

-t  Enter test mode: exit with status 0 when all of the listed job ids are already done, else with status 1.

-w  Enter waiting mode: wait in the foreground until all listed job ids are done.

ENVIRONMENT

NQDIR
    Directory where lock files/job output resides. Each NQDIR can be considered a separate queue. The current working directory is used when NQDIR is unset. NQDIR is created if needed.

NQDONEDIR
    When set, specifies a directory ( must be on the same file system as NQDIR) where lock files/job output is moved to after successful execution of the job.

    Ignored when -c is used.

NQJOBID
    The job id of the currently running job, exposed to the job itself.

FILES
nq owns all files in NQDIR (respectively ~.) which start with “”, or “.,”. These files are created according to the following scheme:

    ,hexadecimal-time-stamp.pid

EXIT STATUS
The nq utility exits 0 on success, and >0 if an error occurs; unless test mode is used, in which case exit status 1 means there is a job running.

On fatal errors, exit codes 111 and 222 are used.

EXAMPLES
Build make(1) targets clean, depends, all, without occupying the terminal:

    % nq make clean
    % nq make depends
    % nq make all
    % fq
    ... look at output, can interrupt with C-c any time
    without stopping the build ...

Simple download queue, accessible from multiple terminals:

    % alias qget='NQDIR=/tmp/downloads nq wget'
    % alias qwait='NQDIR=/tmp/downloads fq -q'
    window1% qget http://mymirror/big1.iso
    window2% qget http://mymirror/big2.iso
    window3% qget http://mymirror/big3.iso
    % qwait
    ... wait for all downloads to finish ...

As nohup(1) replacement (The benchmark will run in background, every run gets a different output file, and the command line you ran is logged too.):

    % ssh remote
    remote% nq ./run-benchmark
    ,14f6f3034f8.17035
    remote% ^D
    % ssh remote
    remote% fq
    ... see output, fq exits when job finished ...

TRICKS
The "file extension" of the log file is actually the PID of the job. nq runs all jobs in a separate process group, so you can kill an entire job process tree at once using kill(1) with a negative PID. Before the job is started, it is the PID of nq, so you can cancel a queued job by killing it as well.

Thanks to the initial exec line in the log files, you can resubmit a job by executing it as a shell command file, i.e. running

    sh job id

Creating nq wrappers setting NQDIR to provide different queues for different purposes is encouraged.

INTERNALS
Enforcing job order works like this:
-   every job has an output file locked using flock(2) and named according to FILES.
-   every job starts only after all earlier flocked files are unlocked.
-   the lock is released by the kernel after the job terminates.

ASSUMPTIONS
nq will only work correctly when:

-   NQDIR (respectively ~.) is writable.

-   flock(2) works correctly in NQDIR (respectively ~.).

-   gettimeofday(2) behaves monotonic (using CLOCK_MONOTONIC would create confusing file names after reboot).

-   No other programs put files matching,* into NQDIR (respectively ~.).

SEE ALSO
fq(1), tq(1).

Alternatives to the nq system include batch(1), qsub(1), schedule(1), srun(1), and ts(1).

AUTHORS
Leah Neukirchen <leah@vuxu.org>

CAVEATS
All reliable queue status information is in main memory only, which makes restarting a job queue after a reboot difficult.

LICENSE
nq is in the public domain.

To the extent possible under law, the creator of this work has waived all copyright and related or neighboring rights to this work.

http://creativecommons.org/publicdomain/zero/1.0/