condor_ssh_to_job — HTCondor Manual
create an ssh session to a running job
condor_ssh_to_job [-help ]
condor_ssh_to_job [-debug ] [-name schedd-name] [-pool pool-name] [-ssh ssh-command] [-keygen-options ssh-keygen-options] [-shells shell1,shell2,...] [-auto-retry ] [-remove-on-interrupt ] cluster | cluster.process | cluster.process.node [remote-command ]
condor_ssh_to_job creates an ssh session to a running job. The job is specified with the argument. If only the job cluster id is given, then the job process id defaults to the value 0.
condor_ssh_to_job is available in Unix HTCondor distributions, and works with two kinds of jobs: those in the vanilla, vm, java, local, or parallel universes, and those jobs in the grid universe which use EC2 resources. It will not work with other grid universe jobs.
For jobs in the vanilla, vm, java, local, or parallel universes, the user must be the owner of the job or must be a queue super user, and both the condor_schedd and condor_starter daemons must allow condor_ssh_to_job access. If no remote-command is specified, an interactive shell is created. An alternate ssh program such as sftp may be specified, using the -ssh option, for uploading and downloading files.
The remote command or shell runs with the same user id as the running job, and it is initialized with the same working directory. The environment is initialized to be the same as that of the job, plus any changes made by the shell setup scripts and any environment variables passed by the ssh client. In addition, the environment variable _CONDOR_JOB_PIDS is defined. It is a space-separated list of PIDs associated with the job. At a minimum, the list will contain the PID of the process started when the job was launched, and it will be the first item in the list. It may contain additional PIDs of other processes that the job has created.
The ssh session and all processes it creates are treated by HTCondor as though they are processes belonging to the job. If the slot is preempted or suspended, the ssh session is killed or suspended along with the job. If the job exits before the ssh session finishes, the slot remains in the Claimed Busy state and is treated as though not all job processes have exited until all ssh sessions are closed. Multiple ssh sessions may be created to the same job at the same time. Resource consumption of the sshd process and all processes spawned by it are monitored by the condor_starter as though these processes belong to the job, so any policies such as PREEMPT that enforce a limit on resource consumption also take into account resources consumed by the ssh session.
condor_ssh_to_job stores ssh keys in temporary files within a newly created and uniquely named directory. The newly created directory will be within the directory defined by the environment variable TMPDIR. When the ssh session is finished, this directory and the ssh keys contained within it are removed.
See the HTCondor administrator's manual section on configuration for details of the configuration variables related to condor_ssh_to_job.
An ssh session works by first authenticating and authorizing a secure connection between condor_ssh_to_job and the condor_starter daemon, using HTCondor protocols. The condor_starter generates an ssh key pair and sends it securely to condor_ssh_to_job. Then the condor_starter spawns sshd in inetd mode with its stdin and stdout attached to the TCP connection from condor_ssh_to_job. condor_ssh_to_job acts as a proxy for the ssh client to communicate with sshd, using the existing connection authorized by HTCondor. At no point is sshd listening on the network for connections or running with any privileges other than that of the user identity running the job. If CCB is being used to enable connectivity to the execute node from outside of a firewall or private network, condor_ssh_to_job is able to make use of CCB in order to form the ssh connection.
The login shell of the user id running the job is used to run the requested command, sshd subsystem, or interactive shell. This is hard-coded behavior in OpenSSH and cannot be overridden by configuration. This means that condor_ssh_to_job access is effectively disabled if the login shell disables access, as in the example programs /bin/true and /sbin/nologin.
condor_ssh_to_job is intended to work with OpenSSH as installed in typical environments. It does not work on Windows platforms. If the ssh programs are installed in non-standard locations, then the paths to these programs will need to be customized within the HTCondor configuration. Versions of ssh other than OpenSSH may work, but they will likely require additional configuration of command-line arguments, changes to the sshd configuration template file, and possibly modification of the $(LIBEXEC)/condor_ssh_to_job_sshd_setup script used by the condor_starter to set up sshd.
For jobs in the grid universe which use EC2 resources, a request that HTCondor have the EC2 service create a new key pair for the job by specifying ec2_keypair_file causes condor_ssh_to_job to attempt to connect to the corresponding instance via ssh. This attempts invokes ssh directly, bypassing the HTCondor networking layer. It supplies ssh with the public DNS name of the instance and the name of the file with the new key pair's private key. For the connection to succeed, the instance must have started an ssh server, and its security group(s) must allow connections on port 22. Conventionally, images will allow logins using the key pair on a single specific account. Because ssh defaults to logging in as the current user, the -l <username> option or its equivalent for other versions of ssh will be needed as part of the remote-command argument. Although the -X option does not apply to EC2 jobs, adding -X or -Y to the remote-command argument can duplicate the effect.
Display brief usage information and exit.
Causes debugging information to be sent to stderr, based on the value of the configuration variable TOOL_DEBUG.
- -name schedd-name
Specify an alternate condor_schedd, if the default (local) one is not desired.
- -pool pool-name
Specify an alternate HTCondor pool, if the default one is not desired. Does not apply to EC2 jobs.
- -ssh ssh-command
Specify an alternate ssh program to run in place of ssh, for example sftp or scp. Additional arguments are specified as ssh-command. Since the arguments are delimited by spaces, place double quote marks around the whole command, to prevent the shell from splitting it into multiple arguments to condor_ssh_to_job. If any arguments must contain spaces, enclose them within single quotes. Does not apply to EC2 jobs.
- -keygen-options ssh-keygen-options
Specify additional arguments to the ssh_keygen program, for creating the ssh key that is used for the duration of the session. For example, a different number of bits could be used, or a different key type than the default. Does not apply to EC2 jobs.
- -shells shell1,shell2,...
Specify a comma-separated list of shells to attempt to launch. If the first shell does not exist on the remote machine, then the following ones in the list will be tried. If none of the specified shells can be found, /bin/sh is used by default. If this option is not specified, it defaults to the environment variable SHELL from within the condor_ssh_to_job environment. Does not apply to EC2 jobs.
Specifies that if the job is not yet running, condor_ssh_to_job should keep trying periodically until it succeeds or encounters some other error.
If specified, attempt to remove the job from the queue if condor_ssh_to_job is interrupted via a CTRL-c or otherwise terminated abnormally.
Enable X11 forwarding. Does not apply to EC2 jobs.
Disable X11 forwarding.
% condor_ssh_to_job 32.0 Welcome to firstname.lastname@example.org! Your condor job is running with pid(s) 65881. % gdb -p 65881 (gdb) where ... % logout Connection to condor-job.tonic.cs.wisc.edu closed.
To upload or download files interactively with sftp:
% condor_ssh_to_job -ssh sftp 32.0 Connecting to condor-job.tonic.cs.wisc.edu... sftp> ls ... sftp> get outputfile.dat
This example shows downloading a file from the job with scp. The string "remote" is used in place of a host name in this example. It is not necessary to insert the correct remote host name, or even a valid one, because the connection to the job is created automatically. Therefore, the placeholder string "remote" is perfectly fine.
% condor_ssh_to_job -ssh scp 32 remote:outputfile.dat .
This example uses condor_ssh_to_job to accomplish the task of running rsync to synchronize a local file with a remote file in the job's working directory. Job id 32.0 is used in place of a host name in this example. This causes rsync to insert the expected job id in the arguments to condor_ssh_to_job.
% rsync -v -e "condor_ssh_to_job" 32.0:outputfile.dat .
Note that condor_ssh_to_job was added to HTCondor in version 7.3. If one uses condor_ssh_to_job to connect to a job on an execute machine running a version of HTCondor older than the 7.3 series, the command will fail with the error message
Failed to send CREATE_JOB_OWNER_SEC_SESSION to starter
condor_ssh_to_job will exit with a non-zero status value if it fails to set up an ssh session. If it succeeds, it will exit with the status value of the remote command or shell.
1990-2021, Center for High Throughput Computing, Computer Sciences Department, University of Wisconsin-Madison, Madison, WI, US. Licensed under the Apache License, Version 2.0.