.. _clush-tool: clush ------- .. highlight:: console *clush* is a program for executing commands in parallel on a cluster and for gathering their results. It can execute commands interactively or can be used within shell scripts and other applications. It is a partial front-end to the :class:`.Task` class of the ClusterShell library (cf. :ref:`class-Task`). *clush* currently makes use of the Ssh worker of ClusterShell that only requires *ssh(1)* (we tested with OpenSSH SSH client). Some features of *clush* command line tool are: * two modes of parallel cluster commands execution: + :ref:`flat mode `: sliding window of local or remote (eg. *ssh(1)*) commands + :ref:`tree mode `: commands propagated to the targets through a tree of pre-configured gateways; gateways are then using a sliding window of local or *ssh(1)* commands to reach the targets (if the target count per gateway is greater than the :ref:`fanout ` value) * smart display of command results (integrated output gathering, sorting by node, nodeset or node groups) * standard input redirection to remote nodes * files copying in parallel * *pdsh* [#]_ options backward compatibility *clush* can be started non-interactively to run a shell command, or can be invoked as an interactive shell. Both modes are discussed here (clush-oneshot clush-interactive). Target and filter nodes ^^^^^^^^^^^^^^^^^^^^^^^ *clush* offers different ways to select or filter target nodes through command line options or files containing a list of hosts. Command line options """""""""""""""""""" The ``-w`` option allows you to specify remote hosts by using ClusterShell :class:`.NodeSet` syntax, including the node groups *@group* special syntax (cf. :ref:`nodeset-groupsexpr`) and the Extended String Patterns syntax (see :ref:`class-NodeSet-extended-patterns`) to benefits from :class:`.NodeSet` basic arithmetic (like ``@Agroup&@Bgroup``). Additionally, the ``-x`` option allows you to exclude nodes from remote hosts list (the same NodeSet syntax can be used here). Nodes exclusion has priority over nodes addition. Using node groups """"""""""""""""" If you have ClusterShell :ref:`node groups ` configured on your cluster, any node group syntax may be used in place of nodes for ``-w`` as well as ``-x``. For example:: $ clush -w @rhel6 cat /proc/loadavg node26: 0.02 0.01 0.00 1/202 23042 For *pdsh* backward compatibility, *clush* supports two ``-g`` and ``-X`` options to respectively select and exclude nodes group(s), but only specified by omitting any *"@"* group prefix (see example below). In general, though, it is advised to use the *@*-prefixed group syntax as the non-prefixed notation is only recognized by *clush* but not by other tools like *nodeset*. For example:: $ clush -g rhel6 cat /proc/loadavg node26: 0.02 0.01 0.00 1/202 23033 .. _clush-all-nodes: Selecting all nodes """"""""""""""""""" The special option ``-a`` (without argument) can be used to select **all** nodes, in the sense of ClusterShell node groups (see :ref:`node groups configuration ` for more details on special **all** external shell command upcall). If not properly configured, the ``-a`` option may lead to a runtime error like:: clush: External error: Not enough working external calls (all, or map + list) defined to get all node .. _clush-pick: Picking node(s) at random """"""""""""""""""""""""" Use ``--pick`` with a maximum number of nodes you wish to pick randomly from the targeted node set. **clush** will then run only on selected node(s). The following example will run a script on a single random node picked from the ``@compute`` group:: $ clush -w @compute --pick=1 ./nonreg-single-client-fs-io.sh Host files """""""""" The option ``--hostfile`` (or ``--machinefile``) may be used to specify a path to a file containing a list of single hosts, node sets or node groups, separated by spaces and lines. It may be specified multiple times (one per file). For example:: $ clush --hostfile ./host_file -b systemctl is-enabled httpd This option has been added as backward compatibility with other parallel shell tools. Indeed, ClusterShell provides a preferred way to provision node sets from node group sources and flat files to all cluster tools using :class:`.NodeSet` (including *clush*). Please see :ref:`node groups configuration `. .. note:: Use ``--debug`` or ``-d`` to see resulting node sets from host files. .. _clush-flat: Flat execution mode ^^^^^^^^^^^^^^^^^^^ The default execution mode is to launch commands (local or remote) in parallel, up to a certain limit fixed by the :ref:`fanout ` value, which is the number of child processes allowed to run at a time. This "sliding window" of active commands is a common technique used on large clusters to conserve resources on the initiating host, while allowing some commands to time out. If used with *ssh(1)*, this does actually limit the number of concurrent ssh connections. .. _clush-fanout: Fanout (sliding window) """"""""""""""""""""""" The ``--fanout`` (or ``-f``) option of **clush** allows the user to change the default *fanout* value defined in :ref:`clush.conf ` or in the :ref:`library defaults ` if not specified. Indeed, it is sometimes useful to change the fanout value for a specific command, for example to avoid flooding a remote service with concurrent requests generated by that actual command. The following example will launch up to ten *puppet* commands at a time on the node group named *@compute*:: $ clush -w @compute -f 10 puppet agent -t If the fanout value is set to 1, commands are executed sequentially:: $ clush -w node[40-42] -f 1 'date +%s; sleep 1' node40: 1505366138 node41: 1505366139 node42: 1505366140 .. _clush-tree: Tree execution mode ^^^^^^^^^^^^^^^^^^^ ClusterShell's tree execution mode is a major horizontal scalability improvement by providing a hierarchical command propagation scheme. The Tree mode of ClusterShell has been the subject of `this paper`_ presented at the Ottawa Linux Symposium Conference in 2012 and at the PyHPC 2013 workshop in Denver, USA. .. highlight:: text The diagram below illustrates the hierarchical command propagation principle with a head node, gateways (GW) and target nodes:: .-----------. | Head node | '-----------' /|\ .------------' | '--.-----------. / | \ \ .-----. .-----. \ .-----. | GW1 | | GW2 | \ | GW3 | '-----' '-----' \ '-----' /|\ /|\ \ |\ .-' | '-. .-' | '-. \ | '---. / | \ / | \ \ | \ .---. .---. .---. .---. .---. .---. .---. .---. .-----. '---' '---' '---' '---' '---' '---' '---' '---' | GW4 | target nodes '-----' | ... The Tree mode is implemented at the library level, so that all applications using ClusterShell may benefits from it. However, this section describes how to use the tree mode with the **clush** command only. .. _clush-tree-enabling: Configuration """"""""""""" The system-wide library configuration file **/etc/clustershell/topology.conf** defines available/preferred routes for the command propagation tree. It is recommended that all connections between parent and children nodes are carefully pre-configured, for example, to avoid any SSH warnings when connecting (if using the default SSH remote worker, of course). .. highlight:: ini The file **topology.conf** is used to define a set of routes under a ``[routes]`` section. Think of it as a routing table but for cluster commands. Node sets should be used when possible, for example:: [routes] rio0: rio[10-13] rio[10-11]: rio[100-240] rio[12-13]: rio[300-440] .. highlight:: text The example above defines the following topology graph:: rio0 |- rio[10-11] | `- rio[100-240] `- rio[12-13] `- rio[300-440] :ref:`nodeset-groups` and :ref:`node-wildcards` are supported in **topology.conf**, but any route definition with an empty node set is ignored (a message is printed in debug mode in that case). At runtime, ClusterShell will pick an initial propagation tree from this topology graph definition and the current root node. Multiple admin/root nodes may be defined in the file. .. note:: The algorithm used in Tree mode does not rely on gateway system hostnames anymore. In topology.conf, just use the hosts or aliases needed to connect to each node. .. highlight:: console Enabling tree mode """""""""""""""""" Since version 1.7, the tree mode is enabled by default when a configuration file is present. When the configuration file **/etc/clustershell/topology.conf** exists, *clush* will use it by default for target nodes that are defined there. The topology file path can be changed using the ``--topology`` command line option. .. note:: If using ``clush -d`` (debug option), clush will display an ASCII representation of the initial propagation tree used. This is useful when working on Tree mode configuration. Enabling tree mode should be as much transparent as possible to the end user. Most **clush** options, including options defined in :ref:`clush.conf ` or specified using ``-O`` or ``-o`` (ssh options) are propagated to the gateways and taken into account there. .. _clush-tree-options: Tree mode specific options """""""""""""""""""""""""" The ``--remote=yes|no`` command line option controls the remote execution behavior: * Default is **yes**, that will make *clush* establish connections up to the leaf nodes using a *distant worker* like *ssh*. * Changing it to **no** will make *clush* establish connections up to the leaf parent nodes only, then the commands are executed locally on the gateways (like if it would be with ``--worker=exec`` on the gateways themselves). This execution mode allows users to schedule remote commands on gateways that take a node as an argument. On large clusters, this is useful to spread the load and resources used of one-shot monitoring, IPMI, or other commands on gateways. A simple example of use is:: $ clush -w node[100-199] --remote=no /usr/sbin/ipmipower -h %h-ipmi -s This command is also valid if you don't have any tree configured, because in that case, ``--remote=no`` is an alias of ``--worker=exec`` worker. The ``--grooming`` command line option allows users to change the grooming delay (float, in seconds). This feature allows gateways to aggregate responses received within a certain timeframe before transmitting them back to the root node in a batch fashion. This contributes to reducing the load on the root node by delegating the first steps of this CPU intensive task to the gateways. .. _clush-tree-fanout: Fanout considerations """"""""""""""""""""" ClusterShell uses a "sliding window" or *fanout* of processes to avoid too many concurrent connections and to conserve resources on the initiating hosts. See :ref:`clush-flat` for more details about this. In tree mode, the same *fanout* value is used on the head node and on each gateway. That is, if the *fanout* is **16**, each gateway will initiate up to **16** connections to their target nodes at the same time. .. note:: This is likely to **change** in the future, as it makes the *fanout* behaviour different if you are using the tree mode or not. For example, some administrators are using a *fanout* value of 1 to "sequentialize" a command on the cluster. In tree mode, please note that in that case, each gateway will be able to run a command at the same time. .. _clush-tree-python: Remote Python executable """""""""""""""""""""""" You must use the same major version of Python on the gateways and the root node. By default, the same python executable name than the one used on the root node will be used to launch the gateways, that is, `python` or `python3` (using relative path for added flexibility). You may override the selection of the remote Python interpreter by defining the following environment variable:: $ export CLUSTERSHELL_GW_PYTHON_EXECUTABLE=/path/to/python3 .. note:: It is highly recommended to have the same Python interpreter installed on all gateways and the root node. Debugging Tree mode """"""""""""""""""" To debug Tree mode, you can define the following environment variable before running **clush** (or any other applications using ClusterShell):: $ export CLUSTERSHELL_GW_LOG_LEVEL=DEBUG (default value is INFO) $ export CLUSTERSHELL_GW_LOG_DIR=/tmp (default value is /tmp) This will generate log files of the form ``$HOSTNAME.gw.log`` in ``CLUSTERSHELL_GW_LOG_DIR``. .. _clush-oneshot: Non-interactive (or one-shot) mode ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ When *clush* is started non-interactively, the command is executed on the specified remote hosts in parallel (given the current *fanout* value and the number of commands to execute (see *fanout* library settings in :ref:`class-Task-configure`). .. _clush-gather: Output gathering options """""""""""""""""""""""" If option ``-b`` or ``--dshbak`` is specified, *clush* waits for command completion while displaying a :ref:`progress indicator ` and then displays gathered output results. If standard output is redirected to a file, *clush* detects it and disable any progress indicator. .. warning:: *clush* will only consolidate identical command outputs if the command return codes are also the same. The following is a simple example of *clush* command used to execute ``uname -r`` on *node40*, *node41* and *node42*, wait for their completion and finally display digested output results:: $ clush -b -w node[40-42] uname -r --------------- node[40-42] --------------- 2.6.35.6-45.fc14.x86_64 It is common to cancel such command execution because a node is hang. When using *pdsh* and *dshbak*, due to the pipe, all nodes output will be lost, even if all nodes have successfully run the command. When you hit CTRL-C with *clush*, the task is canceled but received output is not lost:: $ clush -b -w node[1-5] uname -r Warning: Caught keyboard interrupt! --------------- node[2-4] (3) --------------- 2.6.31.6-145.fc11 --------------- node5 --------------- 2.6.18-164.11.1.el5 Keyboard interrupt (node1 did not complete). .. _clush-diff: Performing *diff* of cluster-wide outputs """"""""""""""""""""""""""""""""""""""""" Since version 1.6, you can use the ``--diff`` *clush* option to show differences between common outputs. This feature is implemented using `Python unified diff`_. This special option implies ``-b`` (gather common stdout outputs) but you don't need to specify it. Example:: $ clush -w node[40-42] --diff dmidecode -s bios-version --- node[40,42] (2) +++ node41 @@ -1,1 +1,1 @@ -1.0.5S56 +1.1c A nodeset is automatically selected as the "reference nodeset" according to these criteria: #. lowest command return code (to discard failed commands) #. largest nodeset with the same output result #. otherwise the first nodeset is taken (ordered (1) by name and (2) lowest range indexes) .. _clush-outdir: Saving output in files """""""""""""""""""""" To save the standard output (stdout) and/or error (stderr) of all remote commands to local files identified with the node name in a given directory, use the options ``--outdir`` and/or ``--errdir``. Any directory that doesn't exist will be automatically created. These options provide a similar functionality as *pssh(1)*. For example, to save all logs from *journalctl(1)* in a local directory ``/tmp/run1/stdout``, you could use:: $ clush -w node[40-42] --outdir=/tmp/run1/stdout/ journalctl >/dev/null Standard input bindings """"""""""""""""""""""" Unless the option ``--nostdin`` (or ``-n``) is specified, *clush* detects when its standard input is connected to a terminal (as determined by *isatty(3)*). If actually connected to a terminal, *clush* listens to standard input when commands are running, waiting for an Enter key press. Doing so will display the status of current nodes. If standard input is not connected to a terminal, and unless the option ``--nostdin`` (or ``-n``) is specified, *clush* binds the standard input of the remote commands to its own standard input, allowing scripting methods like:: $ echo foo | clush -w node[40-42] -b cat --------------- node[40-42] --------------- foo Another stdin-bound *clush* usage example:: $ ssh node10 'ls /etc/yum.repos.d/*.repo' | clush -w node[11-14] -b xargs ls --------------- node[11-14] (4) --------------- /etc/yum.repos.d/cobbler-config.repo .. note:: Use ``--nostdin`` (or ``-n``) in the same way you would use ``ssh -n`` to disable standard input. Indeed, if this option is set, EOF is sent at first read, as if stdin were actually connected to /dev/null. .. _clush-progress: Progress indicator """""""""""""""""" In :ref:`output gathering mode `, *clush* will display a live progress indicator as a simple but convenient way to follow the completion of parallel commands. It can be disabled just by using the ``-q`` or ``--quiet`` options. The progress indicator will appear after 1 to 2 seconds and should look like this:: clush: / If writing is performed to *clush* standard input, like in ``command | clush``, the live progress indicator will display the global bandwidth of data written to the target nodes. Finally, the special option ``--progress`` can be used to force the display of the live progress indicator. Using this option may interfere with some command outputs, but it can be useful when using stdin while remote commands are silent. As an example, the following command will copy a local file to node[1-3] and display the global write bandwidth to the target nodes:: $ dd if=/path/to/local/file | clush -w node[1-3] --progress 'dd of=/path/to/remote/file' clush: 0/3 write: 212.27 MiB/s .. _clush-interactive: Interactive mode ^^^^^^^^^^^^^^^^ If a command is not specified, *clush* runs interactively. In this mode, *clush* uses the *GNU readline* library to read command lines from the terminal. *Readline* provides commands for searching through the command history for lines containing a specified string. For instance, you can type *Control-R* to search in the history for the next entry matching the search string typed so far. Single-character interactive commands """"""""""""""""""""""""""""""""""""" *clush* also recognizes special single-character prefixes that allows the user to see and modify the current nodeset (the nodes where the commands are executed). These single-character interactive commands are detailed below: +------------------------------+-----------------------------------------------+ | Interactive special commands | Comment | +==============================+===============================================+ | ``clush> ?`` | show current nodeset | +------------------------------+-----------------------------------------------+ | ``clush> +`` | add nodes to current nodeset | +------------------------------+-----------------------------------------------+ | ``clush> -`` | remove nodes from current nodeset | +------------------------------+-----------------------------------------------+ | ``clush> @`` | set current nodeset | +------------------------------+-----------------------------------------------+ | ``clush> !`` | execute ```` on the local system | +------------------------------+-----------------------------------------------+ | ``clush> =`` | toggle the output format (gathered or | | | standard mode) | +------------------------------+-----------------------------------------------+ To leave an interactive session, type ``quit`` or *Control-D*. As of version 1.6, it is not possible to cancel a command while staying in *clush* interactive session: for instance, *Control-C* is not supported and will abort current *clush* interactive command (see `ticket #166`_). Example of *clush* interactive session:: $ clush -w node[11-14] -b Enter 'quit' to leave this interactive mode Working with nodes: node[11-14] clush> uname --------------- node[11-14] (4) --------------- Linux clush> !pwd LOCAL: /root clush> -node[11,13] Working with nodes: node[12,14] clush> uname --------------- node[12,14] (2) --------------- Linux clush> The interactive mode and commands described above are subject to change and improvements in future releases. Feel free to open an enhancement `ticket`_ if you use the interactive mode and have some suggestions. .. _clush-copy: File copying mode ^^^^^^^^^^^^^^^^^ When *clush* is started with the ``-c`` or ``--copy`` option, it will attempt to copy specified files and/or directories to the provided cluster nodes. The ``--dest`` option can be used to specify a single path where all the file(s) should be copied to on the target nodes. In the absence of ``--dest``, *clush* will attempt to copy each file or directory found in the command line to their same location on the target nodes. Here are some examples of file copying with *clush*:: $ clush -v -w node[11-12] --copy /tmp/foo `/tmp/foo' -> node[11-12]:`/tmp' $ clush -v -w node[11-12] --copy /tmp/foo /tmp/bar `/tmp/bar' -> node[11-12]:`/tmp' `/tmp/foo' -> node[11-12]:`/tmp' $ clush -v -w node[11-12] --copy /tmp/foo --dest /var/tmp/ `/tmp/foo' -> node[11-12]:`/var/tmp/' .. note:: To copy a file to nodes under a different user, use the ``--user=$USER`` option and **NOT** ``$USER@node[11-12]``. Reverse file copying mode ^^^^^^^^^^^^^^^^^^^^^^^^^ When *clush* is started with the ``--rcopy`` option, it will attempt to retrieve specified file and/or directory from provided cluster nodes. If the ``--dest`` option is specified, it must be a directory path where the files will be stored with their hostname appended. If the destination path is not specified, it will take each file or directory's parent directory as the local destination, for example:: $ clush -v -w node[11-12] --rcopy /tmp/foo node[11-12]:`/tmp/foo' -> `/tmp' $ ls /tmp/foo.* /tmp/foo.node11 /tmp/foo.node12 .. _clush-modes: Run modes ^^^^^^^^^ Since version 1.9, *clush* has support for run modes, which are special :ref:`clush.conf ` settings with a given name. See :ref:`run mode configuration ` for more details on how to install a run mode. This section describes how to use the run modes from the provided example files. To use an installed run mode, just use the ``--mode`` or ``-m`` command line option followed by the mode name (eg. ``sudo``, ``sshpass``, etc.). .. _clush-sshpass: Run mode: sshpass """"""""""""""""" Since version 1.9, *clush* has support for password-based ssh authentication. It is implemented thanks to the external `sshpass`_ tool and provided sshpass run mode example. When using this run mode, you will be prompted for a password that will be forwarded to sshpass. This could be convenient for example in a new environment to install ssh keys on a large number of servers. Make sure you have *sshpass(1)* installed on your operating system and install the sshpass run mode by creating ``sshpass.conf`` in ``clush.conf.d``:: $ cd /etc/clustershell/clush.conf.d # or $CLUSTERSHELL_CFGDIR/clush.conf.d $ cp sshpass.conf.example sshpass.conf Then, run *clush* with ``--mode=sshpass`` (or ``-m sshpass``) to activate this run mode. You will be prompted for a password that will be forwarded on stdin to sshpass to authenticate your ssh workers. The following example shows how to check the date on four servers with password-based ssh authentication:: $ clush -w n[1-2]c[01-02] --mode=sshpass -b date Password: --------------- n[1-2]c[01-02] (4) --------------- Thu Nov 17 16:08:04 PST 2022 The following example shows how to install an ``authorized_keys`` file with the :ref:`clush-copy` and password-based ssh authentication on four nodes:: $ clush -w n[1-2]c[01-02] -m sshpass -v --copy ~/authorized_keys --dest ~/.ssh/authorized_keys [sshpass] run mode activated [sshpass] password prompt enabled Password: `/home/user/authorized_keys' -> n[1-2]c[01-02]:`/home/user/.ssh/authorized_keys' .. _clush-sudo: Run mode: sudo """""""""""""" Since version 1.9, *clush* has support for `sudo`_ password forwarding over stdin. This may be useful in an environment that only allows sysadmins to perform interactive *sudo* work with password. .. warning:: In this section, it is assumed that *sudo* always requires a password for the user on the target nodes. If *sudo* does NOT require any password (i.e. **NOPASSWD** is specified in your sudoers file), you do not need any extra options to run your *sudo* commands with *clush*. Make sure you have *sudo(8)* installed on your operating system. Then install the sudo run mode by creating ``sudo.conf`` in ``clush.conf.d``:: $ cd /etc/clustershell/clush.conf.d # or $CLUSTERSHELL_CFGDIR/clush.conf.d $ cp sudo.conf.example sudo.conf Then, run *clush* with ``--mode=sudo`` (or ``-m sudo``) to **enable a password prompt** to type your *sudo* password, then *sudo* (well, the ``command_prefix`` from the sudo run mode – see below) will be used to run your commands on the target nodes. The password is broadcasted to all target nodes over *ssh(1)* (or via your :ref:`favorite worker `) and as such, must be the same on all target nodes. It is not stored on disk at any time and only kept in memory during the duration of the *clush* command. Thus, the password will be prompted every time you run *clush*. When you start *clush* in :ref:`interactive mode ` along with ``--mode=sudo``, you can run multiple commands in that mode without having to type your password every time. When ``--mode=sudo`` is used, *clush* will run *sudo* for you on each target node, so your command itself should NOT start with ``sudo``. The actual *sudo* command used by *clush* can be changed in ``clush.conf.d/sudo.conf`` or in command line using ``-O command_prefix"..."``. The configured ``command_prefix`` must be able to read a password on stdin followed by a new line (which is what ``sudo -S`` does). Usage example:: $ clush -w n[1-2]c[01-02] --mode=sudo -b id Password: --------------- n[1-2]c[01-02] (4) --------------- uid=0(root) gid=0(root) groups=0(root) Other options ^^^^^^^^^^^^^ Overriding clush.conf settings """""""""""""""""""""""""""""" *clush* default settings are found in a configuration described in :ref:`clush configuration `. To override any settings, use the ``--option`` command line option (or ``-O`` for the shorter version), and repeat as needed. Here is a simple example to disable the use colors in the output nodeset header:: $ clush -O color=never -w node[11-12] -b echo ok --------------- node[11-12] (2) --------------- ok NO_COLOR, CLICOLOR_FORCE and CLICOLOR environment variables can also be used to change the way *clush* uses colors to display messages. .. _clush-worker: Worker selection """""""""""""""" By default, *clush* is using the default library worker configuration when running commands or copying files. In most cases, this is *ssh* (See :ref:`task-default-worker` for default worker selection). Worker selection can be performed at runtime thanks to ``--worker`` command line option (or ``-R`` for the shorter version in order to be compatible with *pdsh* remote command selection option):: $ clush -w node[11-12] --worker=rsh echo ok node11: ok node12: ok By default, ClusterShell supports the following worker identifiers: * **exec**: this local worker supports parallel command execution, doesn't rely on any external tool and provides command line placeholders described below: * ``%h`` and ``%host`` are substituted with each *target hostname* * ``%hosts`` is substituted with the full *target nodeset* * ``%n`` and ``%rank`` are substituted with the remote *rank* (0 to n-1) For example, the following would request the exec worker to locally run multiple *ipmitool* commands across the hosts foo[0-10] and automatically aggregate output results (-b):: $ clush -R exec -w foo[0-10] -b ipmitool -H %h-ipmi chassis power status --------------- foo[0-10] (11) --------------- Chassis Power is on * **rsh**: remote worker based on *rsh* * **ssh**: remote worker based on *ssh* (default) * **pdsh**: remote worker based on *pdsh* that requires *pdsh* to be installed; doesn't provide write support (eg. you cannot ``cat file | clush --worker pdsh``); it is primarily an 1-to-n worker example. Worker modules distributed outside of ClusterShell are also supported by specifying the case-sensitive full Python module name of a worker module. .. [#] LLNL parallel remote shell utility (https://software.llnl.gov/repo/#!/chaos/pdsh) .. _seq(1): http://linux.die.net/man/1/seq .. _Python unified diff: http://docs.python.org/library/difflib.html#difflib.unified_diff .. _ticket #166: https://github.com/cea-hpc/clustershell/issues/166 .. _ticket: https://github.com/cea-hpc/clustershell/issues/new .. _this paper: https://www.kernel.org/doc/ols/2012/ols2012-thiell.pdf .. _sshpass: http://sshpass.sourceforge.net/ .. _sudo: https://www.sudo.ws/