Asynchroneous Parallel ssh
apssh is a tool that aims at running commands remotely using
ssh on a large
number of target nodes at once. It is thus comparable to
parallel-ssh, except that it is
written on top of
apssh comes with a class
SshJob that can be used in conjunction
asynciojobs to write scenarios that are more elaborate than just sending
the same command on a bunch of hosts. This is presented in more details in
This document, along with API reference doc, and changelog, is available at http://apssh.readthedocs.io/
How to get it
apssh requires python-3.5, as it uses the latest syntax constructions
async def and
await instead of the former
[sudo] pip3 install apssh
2 major modes : well-known commands, or local scripts
The usual way to run a command that is already present on the
remote systems, is to do e.g. this (we'll see the
-t option right away)
apssh -t host1 -t host2 hostname
Script mode : using a local script that gets copied over
Now if you need to run a more convoluted command, you can of course quote meta
; and the like, and struggle your way using the same technique.
There is however an other way to achieve this, by writing a local script
(usually a shell or python script) and use the
-s/--script option, to have
apssh copy it on the target nodes before executing it, like e.g.:
apssh -t host1 -t host2 --script mymacros.sh one two
- You can also use this option and provide your own script directly on the command line
$ apssh -s -t r2lab.infra --script 'arg1=$1; shift; arg2=$1; shift; echo exchanged $arg2 $arg1' one two faraday.inria.fr:exchanged two one bemol.pl.sophia.inria.fr:exchanged two one
This will have the effect to perform the following on each target node :
- create if needed a directory named
- copy the local file
mymacros.sh- or your inline script - into that remote dir
.apssh/mymacros.sh one tworemotely in the home directory
Note that in this mode:
- the first argument of the commands part (here
mymacros.sh) should denote a file that exists locally, or be a valid script;
- it does not have to sit in the local directory but will be installed right
- the remote file will be created in mode o755;
- the command executed remotely has its cwd set to the remote home directory.
Global return code
apssh returns 0 if and only if all remote commands complete and return 0
themselves; otherwise it returns 1.
Adding names : the
To run the command
true on hosts
host2 as well on all hostnames
contained in file
hosts.list, do this:
$ apssh -t host1 -t hosts.list -t host2 true
As a matter of fact you can use the
--target option to refer to
- the name of an existing file: in this case, the file is read, lines
#are considered comments and ignored, all the rest is considered a list of hostnames; you can have several hostnames on one line if you want;
- the name of an existing directory: in this case, all the simple files
present in this directory are considered hostnames (see the
--markoption below to see how this feature allows to easily select nodes that are actually online and reachable);
- otherwise, the string is considered a hostname itself, or possibly several space-separated hostnames.
- NOTE that files and directories are also searched in
~/.apssh, so that these shorthands can be defined globally.
So in practice, assuming that:
hosts.outputscontains only 2 files named
hosts.fileis a text file containing the single line
then if you run
apssh -t host1 -t "host2 host3" -t hosts.file -t hosts.dir true
it will cause the
true command to be run on hosts
Excluding names : the
You can specify exclusions, the logic is exactly the same; exclusions are parsed
first, and then hostnames from
--target will be actually added only if they
are not excluded. Which means the order in which you define targets and excludes
does not matter.
So for example if you have all the known nodes in PLE in file
in a separate file
PLE.dns-unknown the subset of the PLE nodes that are
actually unknown to DNS, you can skip them by doing:
$ apssh -l root -t PLE.nodes -x PLE.dns-unknown cat /etc/fedora-release
$ apssh -l root -x PLE.dns-unknown -t PLE.nodes cat /etc/fedora-release
Max connections: the
By default there is no limit on the number of simultaneous connections, which is
likely to be a problem as soon as you go for several tens of hosts, as you would
then run into limitations on open connections in your OS or network. Use
--window to run at most 50 connections at a time
$ apssh -w 50 -t tons-of-nodes true
Users and keys
Running under a different user
--login to specify a specific username globally; or give a
specific user on a given hostname with
So e.g. to run as
host1, but as
$ apssh -l root -t user@host1 -t host2 -t host3 -- true
apssh locates private keys:
If no keys are specified using the
-i command line option
- (A) if an ssh agent can be reached using the
SSH_AUTH_SOCKenvironment variable, and offers a non-empty list of keys,
apsshwill use the keys loaded in the agent (NOTE: use
ssh-addfor managing the keys known to the agent);
- (B) otherwise,
~/.ssh/id_dsaas far as they exist.
If keys are specified on the command line
- (C) That exact list is used for loading private keys.
In both cases
Note that when loading keys from a file - i.e. in cases (B) and (C) above, a passphrase will be prompted at the terminal for each key that is passphrase-protected. Each passphrase gets prompted once for all the target hosts of course.
It results from all this that passphrase-protected keys can be used in
without prompting only if present in an agent.
This behaviour might not be optimal - for example with this logic there is no way to use agent-loaded keys and additional keys. I am eager to receive feedback from users for possible improvements in this area.
Gateway a.k.a. Bouncing a.k.a. Tunnelling
In some cases, the target nodes are not directly addressable from the box that
apssh, and the ssh traffic needs to go through a gateway. This typically
occurs with testbeds where nodes only have private addresses.
For example in the R2lab testbed, you cannot reach nodes directly from the Internet, but you would need to issue something like:
# reaching one individual node with plain ssh $ ssh email@example.com ssh root@fit02 hostname fit02
In such cases, you can specify the gateway username and hostname through the
--gateway option. For example for running the above command on several
R2lab nodes in one
$ apssh -g firstname.lastname@example.org --login root -t "fit02 fit03 fit04" hostname fit04:fit04 fit02:fit02 fit03:fit03
Note that in this case there is a single ssh connection created to the gateway.
Default : on the fly, annotated with hostname
Default is to output every line as they come back, prefixed with associated hostname. As you might expect, stdout goes to stdout and stderr to stderr. Additionally, error messages issued by apssh itself, like e.g. when a host cannot be reached, also goes on stderr.
$ apssh -l root -t alive -- grep VERSION_ID /etc/os-release email@example.com:22 - Connection failed Disconnect Error: Permission denied host2.planetlab.informatik.tu-darmstadt.de:VERSION_ID=23 host3.planetlab.informatik.tu-darmstadt.de:VERSION_ID=23 planetlab1.xeno.cl.cam.ac.uk:VERSION_ID=23 planetlab2.xeno.cl.cam.ac.uk:VERSION_ID=23
In the above trasnscript, there were 5 target hostnames, one of which being
unreachable. The line with
Permission denied goes on stderr, the other ones
Your own format
You can specify a format with the
--format option (see
apssh --help); there
also are a few predefined formats for convenience:
--format '@line@') output is produced as it comes from the host, with no annotation as to which node the line is originating from.
-tc/--time-colon-formatis equivalent to
Subdir : store outputs individually in a dedicated dir
-d options allow to select a specific subdir and to
store results in files named after each hostname. In this case, stdout is
expected to contain a single line that says in which directory results are to be
found (this is useful mostly with
-d, since with
-o you can predict this in
-oit is possible to redirect outputs in a separate directory, in one file per hostname.
-doption behaves like
-owith a name computed from the current time.
$ rm -rf alive.results/ $ apssh -o alive.results -l root -t alive cat /etc/fedora-release alive.results $ grep . alive.results/* alive.results/mars.planetlab.haw-hamburg.de:Fedora release 14 (Laughlin) alive.results/merkur.planetlab.haw-hamburg.de:Fedora release 14 (Laughlin) alive.results/planetlab-2.research.netlab.hut.fi:Fedora release 22 (Twenty Two) alive.results/planetlab1.tlm.unavarra.es:Fedora release 22 (Twenty Two) alive.results/planetlab1.virtues.fi:Fedora release 14 (Laughlin)
When an output subdir is selected with either
option can be used to request details on the retcod from individual nodes. The
way this is exposed in the filesystem under <subdir> is as follows
0ok/hostname will contain 0 for all nodes that could run the command successfully
1failed/hostname will contain the actual retcod, for all nodes that were reached but could not successfully run the command, or
Nonefor the nodes that were not reached at all.
In the example below, we try to talk to two nodes, one of which is not reachable.
$ subdir=$(apssh --mark -d -l root -t planetlab2.tlm.unavarra.es -t uoepl2.essex.ac.uk cat /etc/fedora-release) firstname.lastname@example.org:Connection failed:[Errno 8] nodename nor servname provided, or not known $ echo $subdir 2016-09-01@15:42 $ head -100 $(find $subdir -type f) ==> 2016-09-01@15:42/0ok/planetlab2.tlm.unavarra.es <== 0 ==> 2016-09-01@15:42/1failed/uoepl2.essex.ac.uk <== None ==> 2016-09-01@15:42/planetlab2.tlm.unavarra.es <== Fedora release 18 (Spherical Cow)
- First off, options order matters;
apsshwill stop interpreting options on your command line at the beginning of the remote command. That is to say, in the following example
$ apssh -t host1 -t file1 -t host2 rpm -aq \| grep libvirt
-aq option is meant for the remote
rpm command, and that's fine because after the
apssh stops taking options, and passes them to the remote command instead.
- Also note in the example above that you can pass shell specials,
;and the like, by backslashing them, like this:
$ apssh -l root -t faraday.inria.fr -t r2lab.inria.fr uname -a \; cat /etc/fedora-release /etc/lsb-release 2\> /dev/null r2lab.inria.fr:Linux r2lab.pl.sophia.inria.fr 4.6.4-201.fc23.x86_64 #1 SMP Tue Jul 12 11:43:59 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux r2lab.inria.fr:Fedora release 24 (Twenty Four) faraday.inria.fr:Linux faraday 4.4.0-36-generic #55-Ubuntu SMP Thu Aug 11 18:01:55 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux faraday.inria.fr:DISTRIB_ID=Ubuntu faraday.inria.fr:DISTRIB_RELEASE=16.04 faraday.inria.fr:DISTRIB_CODENAME=xenial faraday.inria.fr:DISTRIB_DESCRIPTION="Ubuntu 16.04.1 LTS"
$ apssh -l root -t PLE.alive.5 -tc uname -r \; hostname 16-47-40:mars.planetlab.haw-hamburg.de:2.6.32-36.onelab.i686 16-47-40:merkur.planetlab.haw-hamburg.de:2.6.32-36.onelab.i686 16-47-40:mars.planetlab.haw-hamburg.de:mars.planetlab.haw-hamburg.de 16-47-40:merkur.planetlab.haw-hamburg.de:merkur.planetlab.haw-hamburg.de 16-47-40:planetlab1.tlm.unavarra.es:4.4.13-200.fc22.x86_64 16-47-40:planetlab1.tlm.unavarra.es:planetlab1.tlm.unavarra.es 16-47-40:planetlab1.virtues.fi:2.6.32-36.onelab.i686 16-47-40:planetlab1.virtues.fi:planetlab1.virtues.fi 16-47-40:planetlab-2.research.netlab.hut.fi:4.2.3-200.fc22.x86_64 16-47-40:planetlab-2.research.netlab.hut.fi:planetlab-2.research.netlab.hut.fi
- brewing something like
appullsounds pretty straightforward, and could turn out most useful; some day probably
- current output system can only properly handle commands output that are
text-based; if your remote command produces binary data instead,
you must redirect its output on the remote system, and fetch the results
later on; note that the binary command
apsshhas no option for doing that, but the API has 2 objects
Pushfor doing this in a more elaborate scenario (see README-jobs.md).
- better tests coverage would not hurt !?!
- probably a lot more features are required for more advanced usages, feel free to fill in issues at https://github.com/parmentelat/apssh.
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