nq: queue utilities
These small utilities allow creating very lightweight job queue systems which require no setup, maintenance, supervision, or any long-running processes.
nq should run on any POSIX.1-2008 compliant system which also
provides a working flock(2). Tested on Linux 2.6.37, Linux 4.1,
OpenBSD 5.7, FreeBSD 10.1, NetBSD 7.0.2, Mac OS X 10.3 and
The intended purpose is ad-hoc queuing of command lines (e.g. for
building several targets of a Makefile, downloading multiple files one
at a time, running benchmarks in several configurations, or simply as
nohup), but as any good Unix tool, it can be abused for
whatever you like.
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
Enforcing job order works like this:
- every job has a flock(2)ed output file ala
- every job starts only after all earlier flock(2)ed files are unlocked
- Why flock(2)? Because it locks the file handle, which is shared
across exec(2) with the child process (the actual job), and it will
unlock when the file is closed (usually when the job terminates).
You enqueue (get it?) new jobs using
nq CMDLINE.... The job id is
output (unless suppressed using
nq detaches immediately,
running the job in the background. STDOUT and STDERR are redirected
into the log file.
nq tries hard (but does not guarantee) to ensure the log file of the
currently running job has +x bit set. Thus you can use
ls -F to get
a quick overview of the state of your queue.
The “file extension” of the log file is actually the PID, so you can
kill jobs easily. Before the job is started, it is the PID of
so you can cancel a queued job by killing it as well.
Due 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
You can wait for jobs to finish using
nq -w, possibly listing job
ids you want to wait for; the default is all of them. Likewise, you
can test if there are jobs which need to be waited upon using
By default, job ids are per-directory, but you can set
$NQDIR to put
them elsewhere. Creating
nq wrappers setting
$NQDIR to provide
different queues for different purposes is encouraged.
All these operations take worst-case quadratic time in the amount of lock files produced, so you should clean them regularly.
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:
% mkdir -p /tmp/downloads % 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 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 ...
nq will only work correctly when:
.) is writable.
flock(2) works in
gettimeofday behaves monotonic (using
create confusing file names). Else job order can be confused and
multiple tasks can run at once due to race conditions.
- No other programs put files matching
Two helper programs are provided:
fq outputs the log of the currently running jobs, exiting when the
jobs are done. If no job is running, the output of the last job is
fq -a shows the output of all jobs,
fq -q only shows one
line per job.
inotify on Linux and falls back to polling
for size change else. (
fq.sh is a similar tool, not quite as robust,
implemented as shell-script calling
nq and displays the
fq output in a new tmux or screen window.
(A pure shell implementation of
nq is provided as
nq.sh. It needs
flock from util-linux, and only has a timer resolution of 1s.
Lock files from
nq.sh should not be mixed.)
make all to build,
make install to install relative to
/usr/local by default). The
DESTDIR convention is respected.
You can also just copy the binaries into your
You can use
make check to run a simple test suite, if you have
atruns jobs at a given time.
batchruns jobs “when system load levels permit”.
task-spoolerrun jobs in sequence with no regard to the system’s load average.
batchhave 52 built-in queues: a-z and A-Z. Any directory can be a queue for
task-spoolercan have different queues for different terminals.
You can follow the output of an
nqqueue tail-style with
The syntax is different:
batchtake whole scripts from the standard input or a file;
nqtakes a single command as its command line arguments.
nqdoesn’t rely on a daemon and relies on a directory to manage the queue.
task-spoolerautomatically launches a daemon to manage a queue.
task-spoolercan set a maximum number of simultaneous jobs.
nq is in the public domain.
To the extent possible under law, Leah Neukirchen email@example.com has waived all copyright and related or neighboring rights to this work.