remote_startup (5) - Linux Manuals

remote_startup: the xxQS_NAMExx remote startup mechanism

NAME

remote_startup - the xxQS_NAMExx remote startup mechanism

DESCRIPTION

xxQS_NAMExx supports several commands to facilitate interactive commands or remote startup of a tightly integrated parallel job. Each command can be set up with (option -sconf) to use different daemons and commands to start the final session. Different startup methods can therefore contain different daemons and commands, and are not related to other startup methods in any way, although it is often desirable to have the same communication method for all startup methods.

Each method requires a separate instance of the communication daemon to be started by for each job, which thus must use a randomly-chosen port, to which the client will try to connect. This is necessary to support tight integration, ensuring that everything for a given job stays in the same process tree and can be properly controlled and accounted by xxQS_NAMExx.

QLOGIN

An interactive qlogin session invoked by will show up in qstat with the default name QLOGIN unless changed by the -N name option. The two entries qlogin_daemon and qlogin_command are responsible for establishing the communication to start such a session.

The default is the value builtin, which will trigger an xxQS_NAME_Sxx internal communication method:

qlogin_command

builtin

qlogin_daemon

builtin

In cases where you want a different communication method, it can also be set up for the formerly-used communication method based on telnet. Despite the fact that telnet is used, there is no need to have telnetd running all the time - xxQS_NAME_Sxx will start a unique one for each job, even when it's from the same user, and telnet can stay disabled as a system service (whether under init or inetd). Only the file /etc/hosts.equiv needs to contain the name of the machines from where a should be allowed. This is often the head node of a cluster, or particular submit machines. Using telnet, the traffic is not encrypted, but that may be reasonable on a private subnet for the cluster, especially if xxQS_NAME_Sxx's CSP security isn't used to secure the system generally.

To achieve this:

qlogin_command

/usr/bin/telnet

qlogin_daemon

/usr/sbin/in.telnetd

must be defined in The defined qlogin_command will then be called with two additional parameters: 'HOST', and 'PORT' in exactly that order, which refer to the machine the qlogin_command should address and the port to be used.

This can also be used to set up secure communication using SSH (which can also provide X and credential forwarding, as well as compression). In this case a small wrapper must be implemented, whose sole purpose is to swap the two given arguments and prepend -p to the port argument. A suitable one is installed as $SGE_ROOT/util/resources/wrappers/qlogin_wrapper:

qlogin_command

/opt/sge/util/resources/wrappers/qlogin_wrapper

qlogin_daemon

/usr/sbin/sshd -i

QRLOGIN

An interactive qrlogin session invoked by without a command will show up in qstat having the default name QRLOGIN unless changed by the -N name option. The two entries rlogin_daemon and rlogin_command are responsible for establishing the command to start such a session.

The default is the value builtin, which will trigger an xxQS_NAME_Sxx internal communication method:

rlogin_command

builtin

rlogin_daemon

builtin

In cases where you want a different communication method, it can follow the formerly-used communication method based on rlogin. As for telnet, rlogin can stay disabled as a system service (whether under init or inetd). Only the file /etc/hosts.equiv needs to contain the name of the machines from where a should be allowed. This is often the head node of a cluster, or particular submit machines. Using rlogin, the traffic is not encrypted, but that may be reasonable on a private subnet for the cluster, especially if xxQS_NAME_Sxx's CSP security isn't used to secure the system generally.

To achieve this:

rlogin_command

$SGE_ROOT/utilbin/$ARC/rlogin

rlogin_daemon

/usr/sbin/in.rlogind

must be defined in The value of $SGE_ROOT must be replaced by the root of the installation, and $ARC must be replaced by the particular platform architecture, as use of environment variables is not implemented for these entries. When the cluster is homogeneous, it can be set to e.g. 'lx-amd64' or 'lx-x86'. In a heterogeneous cluster local configurations need to be defined, where preferably the minority of machines will get local configurations.

The defined rlogin_command will then be called with three additional parameters: '-p','PORT', and 'HOST' in exactly that order, which refer to the machine the rlogin_command should address, and the port to be used.

This can also be used to set up a secure communication using SSH:

rlogin_command

/usr/bin/ssh

rlogin_daemon

/usr/sbin/sshd -i

QRSH

An interactive session for a remote command invoked by with a command will show up in qstat by default with name of the command issued, unless changed by the -N name option. The two entries rsh_daemon and rsh_command are responsible for establishing the communication to start such a session. This startup method will also be used by the master task of a tightly integrated parallel job to start slave processes on other granted exechosts.

The default is the value builtin, which will trigger an xxQS_NAME_Sxx internal communication method:

rsh_command

builtin

rsh_daemon

builtin

In cases where you want a different communication method, it can also be set up for the formerly-used communication method based on rsh. As for telnet, rsh can stay disabled as a system service (whether under init or inetd). Only the file /etc/hosts.equiv needs to contain the name of the machines from where a should be allowed. This is often the head node of a cluster, or particular submit machines. Using rsh, the traffic is not encrypted, but that may be reasonable on a private subnet for the cluster, especially if xxQS_NAME_Sxx's CSP security isn't used to secure the system generally.

To achieve this:

rsh_command

$SGE_ROOT/utilbin/$ARC/rsh

rsh_daemon

$SGE_ROOT/utilbin/$ARC/rshd -l

must be defined in The value of $SGE_ROOT must be replaced by the root of the installation, and $ARC must be replaced by the particular platform architecture, as use of environment variables is not implemented for these entries. When the cluster is homogeneous, it can be set to e.g. 'lx-amd64' or 'lx-x86'. In a heterogeneous cluster local configurations need to be defined, where preferably the minority of machines will get local configurations.

The defined rsh_command will then be called with four additional parameters: '-n', '-p', 'PORT', and 'HOST' in exactly that order, which refer to the machine the rsh_command should address and the port to be used.

This can also be used to set up a secure communication using SSH:

rsh_command

/usr/bin/ssh

rsh_daemon

/usr/sbin/sshd -i

Again, this is independent of SSH as a system service, which can remain disabled.

LOCAL CONFIGURATIONS OF EXECHOSTS

It is important to note that the communication method set up for one particular startup method must match at each end. This can either be achieved by using only a global configuration, or carefully setting up local configurations for the exechosts involved. Whether or not local configurations exist, which must be taken care of, can be checked with qconf -sconfl.

As a general rule, for setting up a communication method between a machine A (where the command is issued) and a machine B (where the daemon is started) it must be guaranteed that the:

setup communication method for the command on machine A
(either global configuration from or local configuration qconf -sconf A of machine A)

matches

setup communication method for the daemon for machine B
(either global configuration from or local configuration qconf -sconf B of machine B)

This way it is also possible to use different communication methods, depending whether a connection from A to B is invoked, or from B to A.

RESTRICTIONS

For all three communication methods, a direct connection between the target and the source machine where the particular command was issued must exist. This can also be implemented using TCP/IP forwarding, but will usually fail if one machine is behind NAT which will mangle the machines' addresses. The communication methods won't work with simple firewalling of the exec hosts since the methods use a random port. It may be possible to set up application-specific firewalling, if necessary, or to wrap the methods and start an SSH tunnel on the port specified for each communication instance.

The builtin method does not support forwarding of X graphics from the compute nodes, or GSSAPI tokens to them. If you need that for any of the remote methods, you will want to set up SSH communication instead.

SSH AUTHENTICATION

To allow the SSH setup explained above to work, the user must be authenticated without the use of a passphrase. While entering a passphrase would still work for interactive commands, it will fail in case of a tightly integrated parallel job, where the master process tries to start a slave process on another exechost.

You can set up passphraseless SSH keys, although this is discouraged. A simpler and global working setup is to use host-based authentication <URL: https://gridengine.sourceforge.io/SGE/howto/hostbased-ssh.html > for the machines inside the cluster.

SSH TIGHT INTEGRATION

To have a tight integration of SSH into xxQS_NAME_Sxx, the started sshd needs an additional group ID to be attached. With this additional group ID, xxQS_NAME_Sxx is able to record the resource consumption and computing time in a correct way. Also a qdel of such a job will be able to succeed.

Such a tight SSH integration can be achieved by two means:

Use of PAM

The easiest way on supported platforms (at least GNU/Linux): a pam(7) module is available for use with the system ssh; it attaches the necessary additional group ID to the started process to provide tight integration. See also the workshop paper <URL: http://gridengine.org/assets/static/ws2007/K5SGE.pdf >.

Recompile xxQS_NAMExx with ./aimk -tight-ssh ...

The source of xxQS_NAMExx contains the necessary additions to compile a modified sshd, which will honor the additional group ID and attach it also to the started process. It's necessary to provide the source of OpenSSH in the directory 3rd_party inside $SGE_ROOT having a plain name 'openssh'. Inside this directory the file sshd.c needs to be patched:

in main():

init_rng();
#ifdef SGESSH_INTEGRATION
sgessh_readconfig();
#endif

in privsep_postauth():

/* Drop privileges */
#ifdef SGESSH_INTEGRATION
sgessh_do_setusercontext(authctxt->pw);
#else
do_setusercontext(authctxt->pw);
#endif

See the original documentation <URL: http://gridengine.org/assets/static/ws2007/SGE-openSSHTightIntegration.RonChen.pdf >.

RESTRICTING ACCESS

With the builtin method in use, there is no need to allow direct access for normal users to compute nodes with ssh etc. However, you may want to allow users to access the nodes for debugging. If you don't want to over-subscribe the nodes, so that qrsh etc. can be used for access, you can use PAM to restrict access for a user only to the nodes on which they have a running job, so as to minimize interference with other others.

There are two possible ways. The cleanest uses Otherwise you can use generic PAM modules, such as pam_limits(8) or pam_access(8), with modifications to their configuration set up and taken down in the job prolog and epilog respectively. See, for instance, a user list message <URL: http://gridengine.markmail.org/message/mu3i7haeshlevu6q?q=282211 >, and other examples of similar prolog/epilog scripts provided with locking in the pam_authuser contribution in the Torque distribution.

SECURITY

See the notes above concerning security of the communication channel.

EXAMPLES

Using SSH with the PAM module, forcing tty allocation, and preventing the delegation of GSSAPI credentials to the compute nodes:

rsh_daemon /opt/sge/util/rshdwrapper
rsh_command ssh -tt -o GSSAPIDelegateCredentials=no
qlogin_daemon /opt/sge/util/rshdwrapper
qlogin_command ssh -tt -o GSSAPIDelegateCredentials=no
rlogin_daemon /opt/sge/util/rshdwrapper
rlogin_command ssh -tt -o GSSAPIDelegateCredentials=no

Old-style method, using telnet and rlogin:

qlogin_command /usr/bin/telnet
qlogin_daemon /usr/sbin/in.telnetd
rlogin_command /opt/sge/utilbin/lx-x86/rlogin
rlogin_daemon /usr/sbin/in.rlogind
rsh_command /opt/sge/utilbin/lx-x86/rsh
rsh_daemon /opt/sge/utilbin/lx-x86/rshd -l

FILES

$SGE_ROOT/util/resources/wrappers/qlogin_wrapper

SSH-based wrapper for qlogin (see above)

AUTHOR

Man page written by Reuti, partly based on Sun material. Some additions by Dave Love.

COPYRIGHT

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